1.
Amedeo Avogadro
–
In tribute to him, the number of elementary entities in 1 mole of a substance,6. 02214179×1023, is known as the Avogadro constant, one of the seven SI base units and represented by NA. Avogadro was born at Turin to a family of Piedmont-Sardinia in the year 1776. That city, now part of Italy, was then of the Kingdom of Sardinia and he graduated in ecclesiastical law at the late age of 20 and began to practice. Soon after, he dedicated himself to physics and mathematics, and in 1809 started teaching them at a liceo in Vercelli, Avogadro submitted this essay to a Jean-Claude Delamétheries Journal de Physique, de Chimie et dHistoire naturelle. In 1820, he became a professor of physics at the University of Turin, Turin was now the capital of the restored Savoyard Kingdom of Sardinia under Victor Emmanuel I. Avogadro was active in the movement of March 1821. As a result, he lost his chair in 1823, eventually, King Charles Albert granted a Constitution in 1848. Well before this, Avogadro had been recalled to the university in Turin in 1833, little is known about Avogadros private life, which appears to have been sober and religious. He married Felicita Mazzé and had eight children, Avogadro held posts dealing with statistics, meteorology, and weights and measures and was a member of the Royal Superior Council on Public Instruction. In honor of Avogadros contributions to theory, the number of molecules in one mole was named Avogadros number. Avogadros number is used to compute the results of chemical reactions and it allows chemists to determine amounts of substances produced in a given reaction to a great degree of accuracy. Johann Josef Loschmidt first calculated the value of Avogadros number, often referred to as the Loschmidt number in German-speaking countries, Avogadros Law states that the relationship between the masses of the same volume of same gases corresponds to the relationship between their respective molecular weights. Hence, the molecular mass of a gas can be calculated from the mass of sample of known volume. Avogadro developed this hypothesis after Joseph Louis Gay-Lussac had published in 1808 his law on volumes, the greatest problem Avogadro had to resolve was the confusion at that time regarding atoms and molecules. One of his most important contributions was clearly distinguishing one from the other, stating that gases are composed of molecules, for instance, John Dalton did not consider this possibility. Avogadro did not actually use the word atom as the words atom and he believed that there were three kinds of molecules, including an elementary molecule. Also, more attention was given to the definition of mass, in 1841, he published his work in Fisica dei corpi ponderabili, ossia Trattato della costituzione materiale de corpi,4 volumes. The scientific community did not give attention to his theory
Amedeo Avogadro
–
Amedeo Avogadro
Amedeo Avogadro
–
Mémoire
2.
Chemistry
–
Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is sometimes called the science because it bridges other natural sciences, including physics. For the differences between chemistry and physics see comparison of chemistry and physics, the history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world. The word chemistry comes from alchemy, which referred to a set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism. An alchemist was called a chemist in popular speech, and later the suffix -ry was added to this to describe the art of the chemist as chemistry, the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία and this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian. Alternately, al-kīmīā may derive from χημεία, meaning cast together, in retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term chymistry, in the view of noted scientist Robert Boyle in 1661, in 1837, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. More recently, in 1998, Professor Raymond Chang broadened the definition of chemistry to mean the study of matter, early civilizations, such as the Egyptians Babylonians, Indians amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didnt develop a systematic theory. Greek atomism dates back to 440 BC, arising in works by such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura, unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments. Work, particularly the development of distillation, continued in the early Byzantine period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis. He formulated Boyles law, rejected the four elements and proposed a mechanistic alternative of atoms. Before his work, though, many important discoveries had been made, the Scottish chemist Joseph Black and the Dutchman J. B. English scientist John Dalton proposed the theory of atoms, that all substances are composed of indivisible atoms of matter. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current, british William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhlers synthesis of urea which proved that organisms were, in theory
Chemistry
–
Solutions of substances in reagent bottles, including
ammonium hydroxide and
nitric acid, illuminated in different colors
Chemistry
–
Democritus ' atomist philosophy was later adopted by
Epicurus (341–270 BCE).
Chemistry
–
Antoine-Laurent de Lavoisier is considered the "Father of Modern Chemistry".
Chemistry
–
Laboratory, Institute of Biochemistry,
University of Cologne.
3.
Physics
–
Physics is the natural science that involves the study of matter and its motion and behavior through space and time, along with related concepts such as energy and force. One of the most fundamental disciplines, the main goal of physics is to understand how the universe behaves. Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy, Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the mechanisms of other sciences while opening new avenues of research in areas such as mathematics. Physics also makes significant contributions through advances in new technologies that arise from theoretical breakthroughs, the United Nations named 2005 the World Year of Physics. Astronomy is the oldest of the natural sciences, the stars and planets were often a target of worship, believed to represent their gods. While the explanations for these phenomena were often unscientific and lacking in evidence, according to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descended from late Babylonian astronomy. The most notable innovations were in the field of optics and vision, which came from the works of many scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna. The most notable work was The Book of Optics, written by Ibn Al-Haitham, in which he was not only the first to disprove the ancient Greek idea about vision, but also came up with a new theory. In the book, he was also the first to study the phenomenon of the pinhole camera, many later European scholars and fellow polymaths, from Robert Grosseteste and Leonardo da Vinci to René Descartes, Johannes Kepler and Isaac Newton, were in his debt. Indeed, the influence of Ibn al-Haythams Optics ranks alongside that of Newtons work of the same title, the translation of The Book of Optics had a huge impact on Europe. From it, later European scholars were able to build the devices as what Ibn al-Haytham did. From this, such important things as eyeglasses, magnifying glasses, telescopes, Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover what are now considered to be the laws of physics. Newton also developed calculus, the study of change, which provided new mathematical methods for solving physical problems. The discovery of new laws in thermodynamics, chemistry, and electromagnetics resulted from greater research efforts during the Industrial Revolution as energy needs increased, however, inaccuracies in classical mechanics for very small objects and very high velocities led to the development of modern physics in the 20th century. Modern physics began in the early 20th century with the work of Max Planck in quantum theory, both of these theories came about due to inaccuracies in classical mechanics in certain situations. Quantum mechanics would come to be pioneered by Werner Heisenberg, Erwin Schrödinger, from this early work, and work in related fields, the Standard Model of particle physics was derived. Areas of mathematics in general are important to this field, such as the study of probabilities, in many ways, physics stems from ancient Greek philosophy
Physics
–
Further information:
Outline of physics
Physics
–
Ancient
Egyptian astronomy is evident in monuments like the
ceiling of Senemut's tomb from the
Eighteenth Dynasty of Egypt.
Physics
–
Sir Isaac Newton (1643–1727), whose
laws of motion and
universal gravitation were major milestones in classical physics
Physics
–
Albert Einstein (1879–1955), whose work on the
photoelectric effect and the
theory of relativity led to a revolution in 20th century physics
4.
Atom
–
An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms, Atoms are very small, typical sizes are around 100 picometers. Atoms are small enough that attempting to predict their behavior using classical physics - as if they were billiard balls, through the development of physics, atomic models have incorporated quantum principles to better explain and predict the behavior. Every atom is composed of a nucleus and one or more bound to the nucleus. The nucleus is made of one or more protons and typically a number of neutrons. Protons and neutrons are called nucleons, more than 99. 94% of an atoms mass is in the nucleus. The protons have an electric charge, the electrons have a negative electric charge. If the number of protons and electrons are equal, that atom is electrically neutral, if an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an ion. The electrons of an atom are attracted to the protons in a nucleus by this electromagnetic force. The number of protons in the nucleus defines to what chemical element the atom belongs, for example, the number of neutrons defines the isotope of the element. The number of influences the magnetic properties of an atom. Atoms can attach to one or more other atoms by chemical bonds to form compounds such as molecules. The ability of atoms to associate and dissociate is responsible for most of the changes observed in nature. The idea that matter is made up of units is a very old idea, appearing in many ancient cultures such as Greece. The word atom was coined by ancient Greek philosophers, however, these ideas were founded in philosophical and theological reasoning rather than evidence and experimentation. As a result, their views on what look like. They also could not convince everybody, so atomism was but one of a number of competing theories on the nature of matter. It was not until the 19th century that the idea was embraced and refined by scientists, in the early 1800s, John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers
Atom
–
Scanning tunneling microscope image showing the individual atoms making up this
gold (
100) surface. The surface atoms deviate from the bulk
crystal structure and arrange in columns several atoms wide with pits between them (See
surface reconstruction).
Atom
–
Helium atom
5.
Molecule
–
A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge, however, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions. In the kinetic theory of gases, the molecule is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules as they are in fact monoatomic molecules. A molecule may be homonuclear, that is, it consists of atoms of one element, as with oxygen, or it may be heteronuclear. Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are not considered single molecules. Molecules as components of matter are common in organic substances and they also make up most of the oceans and atmosphere. Also, no typical molecule can be defined for ionic crystals and covalent crystals, the theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding, which means that solid metals are also not made of molecules. In glasses, atoms may also be together by chemical bonds with no presence of any definable molecule. The science of molecules is called molecular chemistry or molecular physics, in practice, however, this distinction is vague. In molecular sciences, a molecule consists of a system composed of two or more atoms. Polyatomic ions may sometimes be thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i. e, according to Merriam-Webster and the Online Etymology Dictionary, the word molecule derives from the Latin moles or small unit of mass. Molecule – extremely minute particle, from French molécule, from New Latin molecula, diminutive of Latin moles mass, a vague meaning at first, the vogue for the word can be traced to the philosophy of Descartes. The definition of the molecule has evolved as knowledge of the structure of molecules has increased, earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties. Molecules are held together by covalent bonding or ionic bonding. Several types of non-metal elements exist only as molecules in the environment, for example, hydrogen only exists as hydrogen molecule. A molecule of a compound is made out of two or more elements, a covalent bond is a chemical bond that involves the sharing of electron pairs between atoms
Molecule
–
Atomic force microscopy image of a
PTCDA molecule, which contains five carbon rings in a non-linear arrangement.
Molecule
Molecule
–
A
scanning tunneling microscopy image of
pentacene molecules, which consist of linear chains of five carbon rings.
Molecule
–
Arrangement of
polyvinylidene fluoride molecules in a
nanofiber –
transmission electron microscopy image.
6.
Amount of substance
–
Amount of substance is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount, the International System of Units defines the amount of substance to be proportional to the number of elementary entities present. The SI unit for amount of substance is the mole and it has the unit symbol mol. The proportionality constant is the inverse of the Avogadro constant, the mole is defined as the amount of substance that contains an equal number of elementary entities as there are atoms in 12g of the isotope carbon-12. This number is called Avogadros number and has the value 6. 022140857×1023 and it is the numerical value of the Avogadro constant which has the unit 1/mol, and relates the molar mass of an amount of substance to its mass. Therefore, the amount of substance of a sample is calculated as the sample mass divided by the mass of the substance. Amount of substance appears in thermodynamic relations such as the gas law. Another unit of amount of substance in use in engineering in the United States is the pound-mole. When quoting an amount of substance, it is necessary to specify the entity involved, unless there is no risk of ambiguity. One mole of chlorine could refer either to chlorine atoms, as in 58.44 g of sodium chloride, or to chlorine molecules, the simplest way to avoid ambiguity is to replace the term substance by the name of the entity or to quote the empirical formula. The main derived quantity in which amount of substance enters into the numerator is amount of substance concentration and this name is often abbreviated to amount concentration, except in clinical chemistry where substance concentration is the preferred term to avoid ambiguity with mass concentration. The term molar concentration is incorrect, but commonly used, the alchemists, and especially the early metallurgists, probably had some notion of amount of substance, but there are no surviving records of any generalization of the idea beyond a set of recipes. In 1758, Mikhail Lomonosov questioned the idea that mass was the measure of the quantity of matter. The development of the concept of amount of substance was coincidental with, and vital to,1777, Wenzel publishes Lessons on Affinity, in which he demonstrates that the proportions of the base component and the acid component remain the same during reactions between two neutral salts. 1789, Lavoisier publishes Treatise of Elementary Chemistry, introducing the concept of a chemical element,1792, Richter publishes the first volume of Stoichiometry or the Art of Measuring the Chemical Elements. The term stoichiometry is used for the first time, the first tables of equivalent weights are published for acid–base reactions. Richter also notes that, for an acid, the equivalent mass of the acid is proportional to the mass of oxygen in the base. 1794, Prousts Law of definite proportions generalizes the concept of equivalent weights to all types of chemical reaction,1805, Dalton publishes his first paper on modern atomic theory, including a Table of the relative weights of the ultimate particles of gaseous and other bodies
Amount of substance
–
Base quantity
7.
Mole (unit)
–
The mole is the unit of measurement in the International System of Units for amount of substance. This number is expressed by the Avogadro constant, which has a value of 6. 022140857×1023 mol−1, the mole is one of the base units of the SI, and has the unit symbol mol. The mole is used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 →2 H2O implies that 2 moles of dihydrogen and 1 mole of dioxygen react to form 2 moles of water. The mole may also be used to express the number of atoms, ions, the concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution. For example, the relative molecular mass of natural water is about 18.015, therefore. The term gram-molecule was formerly used for essentially the same concept, the term gram-atom has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadros number of atoms, whether isolated or combined in molecules. Thus, for example,1 mole of MgBr2 is 1 gram-molecule of MgBr2 but 3 gram-atoms of MgBr2, in honor of the unit, some chemists celebrate October 23, which is a reference to the 1023 scale of the Avogadro constant, as Mole Day. Some also do the same for February 6 and June 2, thus, by definition, one mole of pure 12C has a mass of exactly 12 g. It also follows from the definition that X moles of any substance will contain the number of molecules as X moles of any other substance. The mass per mole of a substance is called its molar mass, the number of elementary entities in a sample of a substance is technically called its amount. Therefore, the mole is a convenient unit for that physical quantity, one can determine the chemical amount of a known substance, in moles, by dividing the samples mass by the substances molar mass. Other methods include the use of the volume or the measurement of electric charge. The mass of one mole of a substance depends not only on its molecular formula, since the definition of the gram is not mathematically tied to that of the atomic mass unit, the number NA of molecules in a mole must be determined experimentally. The value adopted by CODATA in 2010 is NA =6. 02214129×1023 ±0. 00000027×1023, in 2011 the measurement was refined to 6. 02214078×1023 ±0. 00000018×1023. The number of moles of a sample is the sample mass divided by the mass of the material. The history of the mole is intertwined with that of mass, atomic mass unit, Avogadros number. The first table of atomic mass was published by John Dalton in 1805
Mole (unit)
–
Base units
8.
Mass
–
In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States
Mass
–
Depiction of early
balance scales in the
Papyrus of Hunefer (dated to the
19th dynasty, ca. 1285 BC). The scene shows
Anubis weighing the heart of Hunefer.
Mass
–
The kilogram is one of the seven
SI base units and one of three which is defined ad hoc (i.e. without reference to another base unit).
Mass
–
Galileo Galilei (1636)
Mass
–
Distance traveled by a freely falling ball is proportional to the square of the elapsed time
9.
International System of Units
–
The International System of Units is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, the system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as the result of an initiative began in 1948. It is based on the system of units rather than any variant of the centimetre-gram-second system. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems, the International System of Units has been adopted by most developed countries, however, the adoption has not been universal in all English-speaking countries. The metric system was first implemented during the French Revolution with just the metre and kilogram as standards of length, in the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram, in 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin, in 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI. On 11 July 1792, the proposed the names metre, are, litre and grave for the units of length, area, capacity. The committee also proposed that multiples and submultiples of these units were to be denoted by decimal-based prefixes such as centi for a hundredth, on 10 December 1799, the law by which the metric system was to be definitively adopted in France was passed. Prior to this, the strength of the magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length, a French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention. Initially the convention only covered standards for the metre and the kilogram, one of each was selected at random to become the International prototype metre and International prototype kilogram that replaced the mètre des Archives and kilogramme des Archives respectively. Each member state was entitled to one of each of the prototypes to serve as the national prototype for that country. Initially its prime purpose was a periodic recalibration of national prototype metres. The official language of the Metre Convention is French and the version of all official documents published by or on behalf of the CGPM is the French-language version
International System of Units
–
Stone marking the
Austro-Hungarian /Italian border at
Pontebba displaying
myriametres, a unit of 10 km used in
Central Europe in the 19th century (but since
deprecated).
International System of Units
–
The seven base units in the International System of Units
International System of Units
–
Carl Friedrich Gauss
International System of Units
–
Thomson
10.
Jean Baptiste Perrin
–
For this achievement he was honoured with the Nobel Prize for Physics in 1926. Born in Lille, France, Perrin attended the École Normale Supérieure and he became an assistant at the school during the period of 1894–97 when he began the study of cathode rays and X-rays. He was awarded the degree of docteur ès sciences in 1897, in the same year he was appointed as a lecturer in physical chemistry at the Sorbonne, Paris. He became a professor at the University in 1910, holding this post until the German occupation of France during World War II, in 1895, Perrin showed that cathode rays were of negative electric charge in nature. He determined Avogadros number by several methods and he explained solar energy as due to the thermonuclear reactions of hydrogen. Perrin was the author of a number of books and dissertations, most notable of his publications were, Rayons cathodiques et rayons X, Les Principes, Electrisation de contact, Réalité moléculaire, Matière et Lumière, Lumière et Reaction chimique. Perrin was also the recipient of prestigious awards including the Joule Prize of the Royal Society in 1896. He was twice appointed a member of the Solvay Committee at Brussels in 1911 and he also held memberships with the Royal Society of London and with the Academies of Sciences of Belgium, Sweden, Turin, Prague, Romania and China. He became a Commander of the Legion of Honour in 1926 and was made Commander of the Order of Léopold, in 1919, Perrin proposed that nuclear reactions can provide the source of energy in stars. · In 1927, he founded the Institut de Biologie Physico-Chimique together with chemist André Job, funding was provided by Edmond James de Rothschild. In 1937, Perrin established the Palais de la Découverte, a museum in Paris. Perrin is considered the father of the National Centre for Scientific Research. In 1936, Perrin, now an undersecretary for research, founded the Service Central de la Recherche Scientifique, both institutions were merged under the CNRS umbrella on October 19,1939. His notable students include Pierre Victor Auger, jean Perrin was the father of Francis Perrin, also a physicist. Perrin was an atheist and a socialist and he was an officer in the engineer corps during World War I. When the Germans invaded France in 1940, he escaped to the U. S. A. together with his partner Nine Choucroun and he died in New York City. After the War, in 1948, his remains were transported back to France by the cruiser Jeanne dArc, exposé de thermodynamique /Principles of thermodynamics Traité de chimie physique
Jean Baptiste Perrin
–
Perrin in 1926
11.
Gram-molecule
–
The mole is the unit of measurement in the International System of Units for amount of substance. This number is expressed by the Avogadro constant, which has a value of 6. 022140857×1023 mol−1, the mole is one of the base units of the SI, and has the unit symbol mol. The mole is used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 →2 H2O implies that 2 moles of dihydrogen and 1 mole of dioxygen react to form 2 moles of water. The mole may also be used to express the number of atoms, ions, the concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution. For example, the relative molecular mass of natural water is about 18.015, therefore. The term gram-molecule was formerly used for essentially the same concept, the term gram-atom has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadros number of atoms, whether isolated or combined in molecules. Thus, for example,1 mole of MgBr2 is 1 gram-molecule of MgBr2 but 3 gram-atoms of MgBr2, in honor of the unit, some chemists celebrate October 23, which is a reference to the 1023 scale of the Avogadro constant, as Mole Day. Some also do the same for February 6 and June 2, thus, by definition, one mole of pure 12C has a mass of exactly 12 g. It also follows from the definition that X moles of any substance will contain the number of molecules as X moles of any other substance. The mass per mole of a substance is called its molar mass, the number of elementary entities in a sample of a substance is technically called its amount. Therefore, the mole is a convenient unit for that physical quantity, one can determine the chemical amount of a known substance, in moles, by dividing the samples mass by the substances molar mass. Other methods include the use of the volume or the measurement of electric charge. The mass of one mole of a substance depends not only on its molecular formula, since the definition of the gram is not mathematically tied to that of the atomic mass unit, the number NA of molecules in a mole must be determined experimentally. The value adopted by CODATA in 2010 is NA =6. 02214129×1023 ±0. 00000027×1023, in 2011 the measurement was refined to 6. 02214078×1023 ±0. 00000018×1023. The number of moles of a sample is the sample mass divided by the mass of the material. The history of the mole is intertwined with that of mass, atomic mass unit, Avogadros number. The first table of atomic mass was published by John Dalton in 1805
Gram-molecule
–
Base units
12.
Hydrogen
–
Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
Hydrogen
–
Purple glow in its plasma state
Hydrogen
–
The
Space Shuttle Main Engine burnt hydrogen with oxygen, producing a nearly invisible flame at full thrust.
Hydrogen
–
Spectral lines of hydrogen
Hydrogen
–
First tracks observed in
liquid hydrogen bubble chamber at the
Bevatron
13.
Gram
–
The gram is a metric system unit of mass. Originally defined as the weight of a volume of pure water equal to the cube of the hundredth part of a metre. The only unit symbol for gram that is recognised by the International System of Units is g following the numeric value with a space, the SI does not support the use of abbreviations such as gr, gm or Gm. The word gramme was adopted by the French National Convention in its 1795 decree revising the system as replacing the gravet introduced in 1793. Its definition remained that of the weight of a centimetre of water. French gramme was taken from the Late Latin term gramma and this word, ultimately from Greek γράμμα letter had adopted a specialised meaning in Late Antiquity of one twenty-fourth part of an ounce, corresponding to about 1.14 grams. This use of the term is found in the carmen de ponderibus et mensuris composed around 400 AD, the gram was the fundamental unit of mass in the 19th-century centimetre–gram–second system of units. The gram is today the most widely used unit of measurement for non-liquid ingredients in cooking and grocery shopping worldwide. 1 gram =15.4323583529 grains 1 grain =0.06479891 grams 1 avoirdupois ounce =28.349523125 grams 1 troy ounce =31.1034768 grams 100 grams =3.527396195 ounces 1 gram =5 carats 1 gram =8. 1 gram is roughly equal to 1 small paper clip or pen cap, the Japanese 1 yen coin has a mass of one gram. Conversion of units Duella Gold gram Orders of magnitude Gram at Encyclopædia Britannica
Gram
–
The mass of this pen cap is about 1 gram
14.
Dimensional analysis
–
Converting from one dimensional unit to another is often somewhat complex. Dimensional analysis, or more specifically the method, also known as the unit-factor method, is a widely used technique for such conversions using the rules of algebra. The concept of physical dimension was introduced by Joseph Fourier in 1822, Physical quantities that are measurable have the same dimension and can be directly compared to each other, even if they are originally expressed in differing units of measure. If physical quantities have different dimensions, they cannot be compared by similar units, hence, it is meaningless to ask whether a kilogram is greater than, equal to, or less than an hour. Any physically meaningful equation will have the dimensions on their left and right sides. Checking for dimensional homogeneity is an application of dimensional analysis. Dimensional analysis is routinely used as a check of the plausibility of derived equations and computations. It is generally used to categorize types of quantities and units based on their relationship to or dependence on other units. Many parameters and measurements in the sciences and engineering are expressed as a concrete number – a numerical quantity. Often a quantity is expressed in terms of other quantities, for example, speed is a combination of length and time. Compound relations with per are expressed with division, e. g.60 mi/1 h, other relations can involve multiplication, powers, or combinations thereof. A base unit is a unit that cannot be expressed as a combination of other units, for example, units for length and time are normally chosen as base units. Units for volume, however, can be factored into the units of length. Sometimes the names of units obscure that they are derived units, for example, an ampere is a unit of electric current, which is equivalent to electric charge per unit time and is measured in coulombs per second, so 1 A =1 C/s. Similarly, one newton is 1 kg⋅m/s2, percentages are dimensionless quantities, since they are ratios of two quantities with the same dimensions. In other words, the % sign can be read as 1/100, derivatives with respect to a quantity add the dimensions of the variable one is differentiating with respect to on the denominator. Thus, position has the dimension L, derivative of position with respect to time has dimension LT−1 – length from position, time from the derivative, the second derivative has dimension LT−2. In economics, one distinguishes between stocks and flows, a stock has units of units, while a flow is a derivative of a stock, in some contexts, dimensional quantities are expressed as dimensionless quantities or percentages by omitting some dimensions
Dimensional analysis
–
Base quantity
15.
Nobel Prize in Physics
–
The Nobel Prize in Physics is a yearly award given by the Royal Swedish Academy of Sciences for those who conferred the most outstanding contributions for mankind in the field of physics. The first Nobel Prize in Physics was awarded to German/Dutch physicist Wilhelm Röntgen in recognition of the services he has rendered by the discovery of the remarkable rays. This award is administered by the Nobel Foundation and widely regarded as the most prestigious award that a scientist can receive in physics and it is presented in Stockholm at an annual ceremony on December 10, the anniversary of Nobels death. Through 2016, a total of 203 individuals have been awarded the prize, only two women have won the Nobel Prize in Physics, Marie Curie in 1903, and Maria Goeppert Mayer in 1963. Though Nobel wrote several wills during his lifetime, the last one was written a year before he died and was signed at the Swedish-Norwegian Club in Paris on 27 November 1895. Nobel bequeathed 94% of his assets,31 million Swedish kronor, to establish. Due to the level of surrounding the will, it was not until April 26,1897 that it was approved by the Storting. The executors of his will were Ragnar Sohlman and Rudolf Lilljequist, the members of the Norwegian Nobel Committee who were to award the Peace Prize were appointed shortly after the will was approved. The prize-awarding organisations followed, the Karolinska Institutet on June 7, the Swedish Academy on June 9, the Nobel Foundation then reached an agreement on guidelines for how the Nobel Prize should be awarded. In 1900, the Nobel Foundations newly created statutes were promulgated by King Oscar II, according to Nobels will, The Royal Swedish Academy of sciences were to award the Prize in Physics. A maximum of three Nobel laureates and two different works may be selected for the Nobel Prize in Physics, compared with other Nobel Prizes, the nomination and selection process for the prize in Physics is long and rigorous. This is a key reason why it has grown in importance over the years to become the most important prize in Physics, the Nobel laureates are selected by the Nobel Committee for Physics, a Nobel Committee that consists of five members elected by The Royal Swedish Academy of Sciences. In the first stage begins in September, around 3,000 people – selected university professors, Nobel Laureates in Physics and Chemistry. The completed nomination forms arrive at the Nobel Committee no later than 31 January of the following year and these nominees are scrutinized and discussed by experts who narrow it to approximately fifteen names. The committee submits a report with recommendations on the candidates into the Academy. The Academy then makes the selection of the Laureates in Physics through a majority vote. The names of the nominees are never announced, and neither are they told that they have been considered for the prize. Nomination records are sealed for fifty years, while posthumous nominations are not permitted, awards can be made if the individual died in the months between the decision of the prize committee and the ceremony in December
Nobel Prize in Physics
–
Wilhelm Röntgen (1845–1923), the first recipient of the Nobel Prize in Physics.
Nobel Prize in Physics
–
The Nobel Prize in Physics
Nobel Prize in Physics
–
Three Nobel Laureates in Physics. Front row from left:
Albert A. Michelson (1907),
Albert Einstein (1921) and
Robert A. Millikan (1923).
16.
Johann Josef Loschmidt
–
Jan or Johann Josef Loschmidt, who referred to himself mostly as Josef Loschmidt, was a notable Austrian scientist who performed ground-breaking work in chemistry, physics, and crystal forms. Born in Karlsbad, a located in the Austrian Empire. This was followed by two years of philosophy and mathematics at Pragues Charles University, where Loschmidt met his second important mentor and this was the philosophy professor Franz S. Exner, whose eyesight was failing, and who asked Loschmidt to be his personal reader. Exner was known for his school reforms, which included promoting mathematics. He suggested to Loschmidt, who became a personal friend. In the process of doing this, he became an able mathematician. The era, when Loschmidt gradually developed his ideas on molecular structures, was to be an epoch in science. It was the time when the Kinetic Theory of Gases was being developed and his 1861 booklet, Chemische Studien, proposed two-dimensional representations for over 300 molecules in a style remarkably similar to that used by modern chemists. Among these were aromatic molecules such as benzene, and related triazines, Loschmidt symbolized the benzene nucleus by a large circle, which he said was to indicate the yet-undetermined structure of the compound. In 1865, Loschmidt was the first to estimate the size of the molecules make up the air, his result was only twice the true size. His method allowed the size of any gas molecules to be related to measurable phenomena and this latter quantity is now known as the Loschmidt constant in his honour, and its modern value is 2.69 x 1019 molecules per cubic centimetre at standard temperature and pressure. Loschmidt and his university colleague Ludwig Boltzmann became good friends. His critique of Boltzmanns attempt to derive the law of thermodynamics from kinetic theory became famous as the reversibility paradox. It led Boltzmann to his concept of entropy as a logarithmic tally of the number of microstates corresponding to a given thermodynamic state. Loschmidt retired from university in 1891 and died in 1895 in Vienna and his only child had died before him at the age of ten. - ISBN 0-306-45684-2 John Buckingham, Chasing the Molecule, Sutton Publishing,2004, Gloucestershire
Johann Josef Loschmidt
–
Johann Josef Loschmidt
17.
Ideal gas
–
An ideal gas is a theoretical gas composed of many randomly moving point particles whose only interaction is perfectly elastic collision. The ideal gas concept is useful because it obeys the ideal gas law, an equation of state. One mole of a gas has a volume of 22.710947 litres at STP as defined by IUPAC since 1982. At normal conditions such as temperature and pressure, most real gases behave qualitatively like an ideal gas. Many gases such as nitrogen, oxygen, hydrogen, noble gases, the ideal gas model tends to fail at lower temperatures or higher pressures, when intermolecular forces and molecular size become important. It also fails for most heavy gases, such as many refrigerants, at high pressures, the volume of a real gas is often considerably greater than that of an ideal gas. At low temperatures, the pressure of a gas is often considerably less than that of an ideal gas. At some point of low temperature and high pressure, real gases undergo a phase transition, the model of an ideal gas, however, does not describe or allow phase transitions. These must be modeled by more complex equations of state, the deviation from the ideal gas behaviour can be described by a dimensionless quantity, the compressibility factor, Z. The ideal gas model has been explored in both the Newtonian dynamics and in quantum mechanics, the ideal gas model has also been used to model the behavior of electrons in a metal, and it is one of the most important models in statistical mechanics. There are three classes of ideal gas, the classical or Maxwell–Boltzmann ideal gas, the ideal quantum Bose gas, composed of bosons. The classical ideal gas can be separated into two types, The classical thermodynamic ideal gas and the ideal quantum Boltzmann gas. The ideal quantum Boltzmann gas overcomes this limitation by taking the limit of the quantum Bose gas, the behavior of a quantum Boltzmann gas is the same as that of a classical ideal gas except for the specification of these constants. The ideal gas law is an extension of experimentally discovered gas laws, real fluids at low density and high temperature approximate the behavior of a classical ideal gas. This deviation is expressed as a compressibility factor, the classical thermodynamic properties of an ideal gas can be described by two equations of state. Multiplying the equations representing the three laws, V ∗ V ∗ V = k b a Gives, V ∗ V ∗ V =, under ideal conditions, V = R, that is, P V = n R T. The other equation of state of an ideal gas must express Joules law, in order to switch from macroscopic quantities to microscopic ones, we use n R = N k B where N is the number of gas particles kB is the Boltzmann constant. The probability distribution of particles by velocity or energy is given by the Maxwell speed distribution, the assumption of spherical particles is necessary so that there are no rotational modes allowed, unlike in a diatomic gas
Ideal gas
18.
Pressure
–
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the relative to the ambient pressure. Various units are used to express pressure, Pressure may also be expressed in terms of standard atmospheric pressure, the atmosphere is equal to this pressure and the torr is defined as 1⁄760 of this. Manometric units such as the centimetre of water, millimetre of mercury, Pressure is the amount of force acting per unit area. The symbol for it is p or P, the IUPAC recommendation for pressure is a lower-case p. However, upper-case P is widely used. The usage of P vs p depends upon the field in one is working, on the nearby presence of other symbols for quantities such as power and momentum. Mathematically, p = F A where, p is the pressure, F is the normal force and it relates the vector surface element with the normal force acting on it. It is incorrect to say the pressure is directed in such or such direction, the pressure, as a scalar, has no direction. The force given by the relationship to the quantity has a direction. If we change the orientation of the element, the direction of the normal force changes accordingly. Pressure is distributed to solid boundaries or across arbitrary sections of normal to these boundaries or sections at every point. It is a parameter in thermodynamics, and it is conjugate to volume. The SI unit for pressure is the pascal, equal to one newton per square metre and this name for the unit was added in 1971, before that, pressure in SI was expressed simply in newtons per square metre. Other units of pressure, such as pounds per square inch, the CGS unit of pressure is the barye, equal to 1 dyn·cm−2 or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre, but using the names kilogram, gram, kilogram-force, or gram-force as units of force is expressly forbidden in SI. The technical atmosphere is 1 kgf/cm2, since a system under pressure has potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume. It is therefore related to density and may be expressed in units such as joules per cubic metre. Similar pressures are given in kilopascals in most other fields, where the prefix is rarely used
Pressure
–
Mercury column
Pressure
–
Pressure as exerted by particle collisions inside a closed container.
Pressure
–
The effects of an external pressure of 700bar on an aluminum cylinder with 5mm wall thickness
Pressure
–
low pressure chamber in
Bundesleistungszentrum Kienbaum, Germany
19.
Absolute temperature
–
Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. Thermodynamic temperature is defined by the law of thermodynamics in which the theoretically lowest temperature is the null or zero point. At this point, absolute zero, the constituents of matter have minimal motion. In the quantum-mechanical description, matter at absolute zero is in its ground state, the International System of Units specifies a particular scale for thermodynamic temperature. It uses the Kelvin scale for measurement and selects the point of water at 273.16 K as the fundamental fixing point. Other scales have been in use historically, the Rankine scale, using the degree Fahrenheit as its unit interval, is still in use as part of the English Engineering Units in the United States in some engineering fields. ITS-90 gives a means of estimating the thermodynamic temperature to a very high degree of accuracy. Internal energy is called the heat energy or thermal energy in conditions when no work is done upon the substance by its surroundings. Internal energy may be stored in a number of ways within a substance, each way constituting a degree of freedom. At equilibrium, each degree of freedom will have on average the energy, k B T /2 where k B is the Boltzmann constant. Temperature is a measure of the random submicroscopic motions and vibrations of the constituents of matter. These motions comprise the internal energy of a substance, more specifically, the thermodynamic temperature of any bulk quantity of matter is the measure of the average kinetic energy per classical degree of freedom of its constituent particles. Translational motions are almost always in the classical regime, translational motions are ordinary, whole-body movements in three-dimensional space in which particles move about and exchange energy in collisions. Figure 1 below shows translational motion in gases, Figure 4 below shows translational motion in solids, Zero kinetic energy remains in a substance at absolute zero. Throughout the scientific world where measurements are made in SI units, many engineering fields in the U. S. however, measure thermodynamic temperature using the Rankine scale. By international agreement, the kelvin and its scale are defined by two points, absolute zero, and the triple point of Vienna Standard Mean Ocean Water. Absolute zero, the lowest possible temperature, is defined as being precisely 0 K, the triple point of water is defined as being precisely 273.16 K and 0.01 °C. This definition does three things, It fixes the magnitude of the unit as being precisely 1 part in 273.15 kelvins
Absolute temperature
–
Fig. 6 Ice and water: two phases of the same substance
Absolute temperature
Absolute temperature
–
Fig. 8 When many of the chemical elements, such as the
noble gases and
platinum-group metals, freeze to a solid — the most ordered state of matter — their
crystal structures have a
closest-packed arrangement. This yields the greatest possible packing density and the lowest energy state.
Absolute temperature
–
Helium-4, is a
superfluid at or below 2.17 kelvins, (2.17 Celsius degrees above
absolute zero)
20.
German-language
–
German is a West Germanic language that is mainly spoken in Central Europe. It is the most widely spoken and official language in Germany, Austria, Switzerland, South Tyrol, the German-speaking Community of Belgium and it is also one of the three official languages of Luxembourg. Major languages which are most similar to German include other members of the West Germanic language branch, such as Afrikaans, Dutch, English, Luxembourgish and it is the second most widely spoken Germanic language, after English. One of the languages of the world, German is the first language of about 95 million people worldwide. The German speaking countries are ranked fifth in terms of publication of new books. German derives most of its vocabulary from the Germanic branch of the Indo-European language family, a portion of German words are derived from Latin and Greek, and fewer are borrowed from French and English. With slightly different standardized variants, German is a pluricentric language, like English, German is also notable for its broad spectrum of dialects, with many unique varieties existing in Europe and also other parts of the world. The history of the German language begins with the High German consonant shift during the migration period, when Martin Luther translated the Bible, he based his translation primarily on the standard bureaucratic language used in Saxony, also known as Meißner Deutsch. Copies of Luthers Bible featured a long list of glosses for each region that translated words which were unknown in the region into the regional dialect. Roman Catholics initially rejected Luthers translation, and tried to create their own Catholic standard of the German language – the difference in relation to Protestant German was minimal. It was not until the middle of the 18th century that a widely accepted standard was created, until about 1800, standard German was mainly a written language, in urban northern Germany, the local Low German dialects were spoken. Standard German, which was different, was often learned as a foreign language with uncertain pronunciation. Northern German pronunciation was considered the standard in prescriptive pronunciation guides though, however, German was the language of commerce and government in the Habsburg Empire, which encompassed a large area of Central and Eastern Europe. Until the mid-19th century, it was essentially the language of townspeople throughout most of the Empire and its use indicated that the speaker was a merchant or someone from an urban area, regardless of nationality. Some cities, such as Prague and Budapest, were gradually Germanized in the years after their incorporation into the Habsburg domain, others, such as Pozsony, were originally settled during the Habsburg period, and were primarily German at that time. Prague, Budapest and Bratislava as well as cities like Zagreb, the most comprehensive guide to the vocabulary of the German language is found within the Deutsches Wörterbuch. This dictionary was created by the Brothers Grimm and is composed of 16 parts which were issued between 1852 and 1860, in 1872, grammatical and orthographic rules first appeared in the Duden Handbook. In 1901, the 2nd Orthographical Conference ended with a standardization of the German language in its written form
German-language
–
Old Frisian (Alt-Friesisch)
German-language
–
German
German-language
–
The widespread popularity of the
Bible translated into German by
Martin Luther helped establish modern German
German-language
–
Examples of German language in
Namibian everyday life
21.
Units of measurement
–
A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same quantity. Any other value of quantity can be expressed as a simple multiple of the unit of measurement. For example, length is a physical quantity, the metre is a unit of length that represents a definite predetermined length. When we say 10 metres, we actually mean 10 times the definite predetermined length called metre, the definition, agreement, and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day. Different systems of units used to be very common, now there is a global standard, the International System of Units, the modern form of the metric system. In trade, weights and measures is often a subject of regulation, to ensure fairness. The International Bureau of Weights and Measures is tasked with ensuring worldwide uniformity of measurements, metrology is the science for developing nationally and internationally accepted units of weights and measures. In physics and metrology, units are standards for measurement of quantities that need clear definitions to be useful. Reproducibility of experimental results is central to the scientific method, a standard system of units facilitates this. Scientific systems of units are a refinement of the concept of weights, science, medicine, and engineering often use larger and smaller units of measurement than those used in everyday life and indicate them more precisely. The judicious selection of the units of measurement can aid researchers in problem solving, in the social sciences, there are no standard units of measurement and the theory and practice of measurement is studied in psychometrics and the theory of conjoint measurement. A unit of measurement is a quantity of a physical property. Units of measurement were among the earliest tools invented by humans, primitive societies needed rudimentary measures for many tasks, constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials. Weights and measures are mentioned in the Bible and it is a commandment to be honest and have fair measures. As of the 21st Century, multiple unit systems are used all over the world such as the United States Customary System, the British Customary System, however, the United States is the only industrialized country that has not yet completely converted to the Metric System. The systematic effort to develop an acceptable system of units dates back to 1790 when the French National Assembly charged the French Academy of Sciences to come up such a unit system. After this treaty was signed, a General Conference of Weights, the CGPM produced the current SI system which was adopted in 1954 at the 10th conference of weights and measures. Currently, the United States is a society which uses both the SI system and the US Customary system
Units of measurement
–
The former Weights and Measures office in
Seven Sisters, London
Units of measurement
–
Units of measurement,
Palazzo della Ragione,
Padua
Units of measurement
–
An example of
metrication in 1860 when Tuscany became part of modern Italy (ex. one "libbra" = 339,54 grams)
22.
Robert Millikan
–
Millikan graduated from Oberlin College in 1891 and obtained his doctorate at Columbia University in 1895. In 1896 he became an assistant at the University of Chicago, in 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron. He began by measuring the course of charged water droplets in an electric field, the results suggested that the charge on the droplets is a multiple of the elementary electric charge, but the experiment was not accurate enough to be convincing. He obtained more precise results in 1910 with his famous experiment in which he replaced water with oil. In 1914 Millikan took up with skill the experimental verification of the equation introduced by Albert Einstein in 1905 to describe the photoelectric effect. He used this research to obtain an accurate value of Planck’s constant. In 1921 Millikan left the University of Chicago to become director of the Norman Bridge Laboratory of Physics at the California Institute of Technology in Pasadena, there he undertook a major study of the radiation that the physicist Victor Hess had detected coming from outer space. Millikan proved that this radiation is indeed of extraterrestrial origin, as chairman of the Executive Council of Caltech from 1921 until his retirement in 1945, Millikan helped to turn the school into one of the leading research institutions in the United States. He also served on the board of trustees for Science Service, now known as Society for Science & the Public, Robert Andrews Millikan was born on March 22,1868, in Morrison, Illinois. Millikan went to school in Maquoketa, Iowa. Millikan received a degree in the classics from Oberlin College in 1891. At the close of my sophomore year my Greek professor asked me to teach the course in physics in the preparatory department during the next year. To my reply that I did not know any physics at all, his answer was, all right, said I, you will have to take the consequences, but I will try and see what I can do with it. I at once purchased an Averys Elements of Physics, and spent the part of my summer vacation of 1889 at home – trying to master the subject. I doubt if I have ever taught better in my life than in my first course in physics in 1889, I was so intensely interested in keeping my knowledge ahead of that of the class that they may have caught some of my own interest and enthusiasm. Millikans enthusiasm for education continued throughout his career, and he was the coauthor of a popular and influential series of introductory textbooks, compared to other books of the time, they treated the subject more in the way in which it was thought about by physicists. They also included many problems that asked conceptual questions, rather than simply requiring the student to plug numbers into a formula. In 1902 he married Greta Ervin Blanchard and they had three sons, Clark Blanchard, Glenn Allan, and Max Franklin
Robert Millikan
–
Robert A. Millikan
Robert Millikan
–
Millikan’s original oil-drop apparatus, circa 1909–1910
Robert Millikan
–
Robert A. Millikan around 1923
23.
Michael Faraday
–
Michael Faraday FRS was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction, diamagnetism, although Faraday received little formal education, he was one of the most influential scientists in history. It was by his research on the field around a conductor carrying a direct current that Faraday established the basis for the concept of the electromagnetic field in physics. Faraday also established that magnetism could affect rays of light and that there was a relationship between the two phenomena. He similarly discovered the principles of induction and diamagnetism. His inventions of electromagnetic rotary devices formed the foundation of electric motor technology, Faraday ultimately became the first and foremost Fullerian Professor of Chemistry at the Royal Institution of Great Britain, a lifetime position. James Clerk Maxwell took the work of Faraday and others and summarized it in a set of equations which is accepted as the basis of all theories of electromagnetic phenomena. The SI unit of capacitance is named in his honour, the farad, albert Einstein kept a picture of Faraday on his study wall, alongside pictures of Isaac Newton and James Clerk Maxwell. Faraday was born in Newington Butts, which is now part of the London Borough of Southwark but was then a part of Surrey. His family was not well off and his father, James, was a member of the Glassite sect of Christianity. James Faraday moved his wife and two children to London during the winter of 1790 from Outhgill in Westmorland, where he had been an apprentice to the village blacksmith, Michael was born in the autumn of that year. The young Michael Faraday, who was the third of four children, at the age of 14 he became an apprentice to George Riebau, a local bookbinder and bookseller in Blandford Street. During his seven-year apprenticeship Faraday read many books, including Isaac Wattss The Improvement of the Mind, at this time he also developed an interest in science, especially in electricity. Faraday was particularly inspired by the book Conversations on Chemistry by Jane Marcet, many of the tickets for these lectures were given to Faraday by William Dance, who was one of the founders of the Royal Philharmonic Society. Faraday subsequently sent Davy a 300-page book based on notes that he had taken during these lectures, davys reply was immediate, kind, and favourable. In 1813, when Davy damaged his eyesight in an accident with nitrogen trichloride, very soon Davy entrusted Faraday with the preparation of nitrogen trichloride samples, and they both were injured in an explosion of this very sensitive substance. In the class-based English society of the time, Faraday was not considered a gentleman, Faraday was forced to fill the role of valet as well as assistant throughout the trip. Davys wife, Jane Apreece, refused to treat Faraday as an equal, the trip did, however, give him access to the scientific elite of Europe and exposed him to a host of stimulating ideas
Michael Faraday
–
Michael Faraday, 1842
Michael Faraday
–
External video
Michael Faraday
–
Portrait of Faraday in his late thirties
Michael Faraday
–
Michael Faraday, ca. 1861
24.
Oxygen
–
Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
Oxygen
–
Spectral lines of oxygen
Oxygen
Oxygen
–
A trickle of liquid oxygen is deflected by a magnetic field, illustrating its paramagnetic property
Oxygen
–
Oxygen discharge (spectrum) tube. The green color is similar to the color of an
"aurora borealis"
25.
SI base unit
–
The International System of Units defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science, thus, the kelvin, named after Lord Kelvin, has the symbol K and the ampere, named after André-Marie Ampère, has the symbol A. Many other units, such as the litre, are not part of the SI. The definitions of the units have been modified several times since the Metre Convention in 1875. Since the redefinition of the metre in 1960, the kilogram is the unit that is directly defined in terms of a physical artifact. However, the mole, the ampere, and the candela are linked through their definitions to the mass of the platinum–iridium cylinder stored in a vault near Paris. It has long been an objective in metrology to define the kilogram in terms of a fundamental constant, two possibilities have attracted particular attention, the Planck constant and the Avogadro constant. The 23rd CGPM decided to postpone any formal change until the next General Conference in 2011
SI base unit
–
The seven SI base units and the interdependency of their definitions: for example, to extract the definition of the metre from the
speed of light, the definition of the second must be known while the
ampere and
candela are both dependent on the definition of
energy which in turn is defined in terms of
length,
mass and
time.
26.
Unit of measurement
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A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same quantity. Any other value of quantity can be expressed as a simple multiple of the unit of measurement. For example, length is a physical quantity, the metre is a unit of length that represents a definite predetermined length. When we say 10 metres, we actually mean 10 times the definite predetermined length called metre, the definition, agreement, and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day. Different systems of units used to be very common, now there is a global standard, the International System of Units, the modern form of the metric system. In trade, weights and measures is often a subject of regulation, to ensure fairness. The International Bureau of Weights and Measures is tasked with ensuring worldwide uniformity of measurements, metrology is the science for developing nationally and internationally accepted units of weights and measures. In physics and metrology, units are standards for measurement of quantities that need clear definitions to be useful. Reproducibility of experimental results is central to the scientific method, a standard system of units facilitates this. Scientific systems of units are a refinement of the concept of weights, science, medicine, and engineering often use larger and smaller units of measurement than those used in everyday life and indicate them more precisely. The judicious selection of the units of measurement can aid researchers in problem solving, in the social sciences, there are no standard units of measurement and the theory and practice of measurement is studied in psychometrics and the theory of conjoint measurement. A unit of measurement is a quantity of a physical property. Units of measurement were among the earliest tools invented by humans, primitive societies needed rudimentary measures for many tasks, constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials. Weights and measures are mentioned in the Bible and it is a commandment to be honest and have fair measures. As of the 21st Century, multiple unit systems are used all over the world such as the United States Customary System, the British Customary System, however, the United States is the only industrialized country that has not yet completely converted to the Metric System. The systematic effort to develop an acceptable system of units dates back to 1790 when the French National Assembly charged the French Academy of Sciences to come up such a unit system. After this treaty was signed, a General Conference of Weights, the CGPM produced the current SI system which was adopted in 1954 at the 10th conference of weights and measures. Currently, the United States is a society which uses both the SI system and the US Customary system
Unit of measurement
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The former Weights and Measures office in
Seven Sisters, London
Unit of measurement
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Units of measurement,
Palazzo della Ragione,
Padua
Unit of measurement
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An example of
metrication in 1860 when Tuscany became part of modern Italy (ex. one "libbra" = 339,54 grams)
27.
Pound mole
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The mole is the unit of measurement in the International System of Units for amount of substance. This number is expressed by the Avogadro constant, which has a value of 6. 022140857×1023 mol−1, the mole is one of the base units of the SI, and has the unit symbol mol. The mole is used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 →2 H2O implies that 2 moles of dihydrogen and 1 mole of dioxygen react to form 2 moles of water. The mole may also be used to express the number of atoms, ions, the concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution. For example, the relative molecular mass of natural water is about 18.015, therefore. The term gram-molecule was formerly used for essentially the same concept, the term gram-atom has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadros number of atoms, whether isolated or combined in molecules. Thus, for example,1 mole of MgBr2 is 1 gram-molecule of MgBr2 but 3 gram-atoms of MgBr2, in honor of the unit, some chemists celebrate October 23, which is a reference to the 1023 scale of the Avogadro constant, as Mole Day. Some also do the same for February 6 and June 2, thus, by definition, one mole of pure 12C has a mass of exactly 12 g. It also follows from the definition that X moles of any substance will contain the number of molecules as X moles of any other substance. The mass per mole of a substance is called its molar mass, the number of elementary entities in a sample of a substance is technically called its amount. Therefore, the mole is a convenient unit for that physical quantity, one can determine the chemical amount of a known substance, in moles, by dividing the samples mass by the substances molar mass. Other methods include the use of the volume or the measurement of electric charge. The mass of one mole of a substance depends not only on its molecular formula, since the definition of the gram is not mathematically tied to that of the atomic mass unit, the number NA of molecules in a mole must be determined experimentally. The value adopted by CODATA in 2010 is NA =6. 02214129×1023 ±0. 00000027×1023, in 2011 the measurement was refined to 6. 02214078×1023 ±0. 00000018×1023. The number of moles of a sample is the sample mass divided by the mass of the material. The history of the mole is intertwined with that of mass, atomic mass unit, Avogadros number. The first table of atomic mass was published by John Dalton in 1805
Pound mole
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Base units
28.
Ounce mole
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The mole is the unit of measurement in the International System of Units for amount of substance. This number is expressed by the Avogadro constant, which has a value of 6. 022140857×1023 mol−1, the mole is one of the base units of the SI, and has the unit symbol mol. The mole is used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 →2 H2O implies that 2 moles of dihydrogen and 1 mole of dioxygen react to form 2 moles of water. The mole may also be used to express the number of atoms, ions, the concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution. For example, the relative molecular mass of natural water is about 18.015, therefore. The term gram-molecule was formerly used for essentially the same concept, the term gram-atom has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadros number of atoms, whether isolated or combined in molecules. Thus, for example,1 mole of MgBr2 is 1 gram-molecule of MgBr2 but 3 gram-atoms of MgBr2, in honor of the unit, some chemists celebrate October 23, which is a reference to the 1023 scale of the Avogadro constant, as Mole Day. Some also do the same for February 6 and June 2, thus, by definition, one mole of pure 12C has a mass of exactly 12 g. It also follows from the definition that X moles of any substance will contain the number of molecules as X moles of any other substance. The mass per mole of a substance is called its molar mass, the number of elementary entities in a sample of a substance is technically called its amount. Therefore, the mole is a convenient unit for that physical quantity, one can determine the chemical amount of a known substance, in moles, by dividing the samples mass by the substances molar mass. Other methods include the use of the volume or the measurement of electric charge. The mass of one mole of a substance depends not only on its molecular formula, since the definition of the gram is not mathematically tied to that of the atomic mass unit, the number NA of molecules in a mole must be determined experimentally. The value adopted by CODATA in 2010 is NA =6. 02214129×1023 ±0. 00000027×1023, in 2011 the measurement was refined to 6. 02214078×1023 ±0. 00000018×1023. The number of moles of a sample is the sample mass divided by the mass of the material. The history of the mole is intertwined with that of mass, atomic mass unit, Avogadros number. The first table of atomic mass was published by John Dalton in 1805
Ounce mole
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Base units
29.
Atomic unit
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Atomic units form a system of natural units which is especially convenient for atomic physics calculations. There are two different kinds of units, Hartree atomic units and Rydberg atomic units, which differ in the choice of the unit of mass. In Hartree units, the speed of light is approximately 137, atomic units are often abbreviated a. u. or au, not to be confused with the same abbreviation used also for astronomical units, arbitrary units, and absorbance units in different contexts. Atomic units, like SI units, have a unit of mass, a unit of length, however, the use and notation is somewhat different from SI. Suppose a particle with a mass of m has 3.4 times the mass of electron, the value of m can be written in three ways, m =3.4 m e. This is the clearest notation, where the unit is included explicitly as a symbol. This notation is ambiguous, Here, it means that the m is 3.4 times the atomic unit of mass. But if a length L were 3.4 times the unit of length. The dimension needs to be inferred from context and this notation is similar to the previous one, and has the same dimensional ambiguity. It comes from setting the atomic units to 1, in this case m e =1. These four fundamental constants form the basis of the atomic units, therefore, their numerical values in the atomic units are unity by definition. Dimensionless physical constants retain their values in any system of units, of particular importance is the fine-structure constant α = e 2 ℏ c ≈1 /137. This immediately gives the value of the speed of light, expressed in atomic units, below are given a few derived units. Some of them have names and symbols assigned, as indicated in the table. There are two variants of atomic units, one where they are used in conjunction with SI units for electromagnetism. Although the units written above are the same way, the units related to magnetism are not. In the SI system, the unit for magnetic field is 1 a. u. = ℏ e a 02 =2. 35×105 T =2. 35×109 G, and in the Gaussian-cgs unit system, = e a 02 c =1. 72×103 T =1. 72×107 G
Atomic unit
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Base units
30.
Boltzmann constant
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The Boltzmann constant, which is named after Ludwig Boltzmann, is a physical constant relating the average kinetic energy of particles in a gas with the temperature of the gas. It is the gas constant R divided by the Avogadro constant NA, the Boltzmann constant has the dimension energy divided by temperature, the same as entropy. The accepted value in SI units is 6977138064851999999♠1. 38064852×10−23 J/K, the Boltzmann constant, k, is a bridge between macroscopic and microscopic physics. Introducing the Boltzmann constant transforms the gas law into an alternative form, p V = N k T. For n =1 mol, N is equal to the number of particles in one mole, given a thermodynamic system at an absolute temperature T, the average thermal energy carried by each microscopic degree of freedom in the system is on the order of magnitude of 1/2kT. In classical statistical mechanics, this average is predicted to hold exactly for homogeneous ideal gases, monatomic ideal gases possess three degrees of freedom per atom, corresponding to the three spatial directions, which means a thermal energy of 3/2kT per atom. This corresponds very well with experimental data, the thermal energy can be used to calculate the root-mean-square speed of the atoms, which turns out to be inversely proportional to the square root of the atomic mass. The root mean square speeds found at room temperature accurately reflect this, ranging from 7003137000000000000♠1370 m/s for helium, kinetic theory gives the average pressure p for an ideal gas as p =13 N V m v 2 ¯. Combination with the gas law p V = N k T shows that the average translational kinetic energy is 12 m v 2 ¯ =32 k T. Considering that the translational motion velocity vector v has three degrees of freedom gives the energy per degree of freedom equal to one third of that. Diatomic gases, for example, possess a total of six degrees of freedom per molecule that are related to atomic motion. Again, it is the energy-like quantity kT that takes central importance, consequences of this include the Arrhenius equation in chemical kinetics. This equation, which relates the details, or microstates. Such is its importance that it is inscribed on Boltzmanns tombstone, the constant of proportionality k serves to make the statistical mechanical entropy equal to the classical thermodynamic entropy of Clausius, Δ S = ∫ d Q T. One could choose instead a rescaled dimensionless entropy in terms such that S ′ = ln W, Δ S ′ = ∫ d Q k T. This is a natural form and this rescaled entropy exactly corresponds to Shannons subsequent information entropy. The characteristic energy kT is thus the required to increase the rescaled entropy by one nat. The iconic terse form of the equation S = k ln W on Boltzmanns tombstone is in due to Planck
Boltzmann constant
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Boltzmann's grave in the
Zentralfriedhof, Vienna, with bust and entropy formula.
. doi:10.1103/RevModPhys.80.633. Direct link to value.
