J. J. Thomson
Sir Joseph John Thomson was an English physicist and Nobel Laureate in Physics, credited with the discovery and identification of the electron, the first subatomic particle to be discovered. In 1897, Thomson showed that cathode rays were composed of unknown negatively charged particles, which he calculated must have bodies much smaller than atoms and a large charge-to-mass ratio. Thomson is credited with finding the first evidence for isotopes of a stable element in 1913, as part of his exploration into the composition of canal rays, his experiments to determine the nature of positively charged particles, with Francis William Aston, were the first use of mass spectrometry and led to the development of the mass spectrograph. Thomson was awarded the 1906 Nobel Prize in Physics for his work on the conduction of electricity in gases. Joseph John Thomson was born 18 December 1856 in Cheetham Hill, Lancashire, England, his mother, Emma Swindells, came from a local textile family. His father, Joseph James Thomson, ran.
He had a brother, Frederick Vernon Thomson, two years younger than he was. J. J. Thomson was a devout Anglican, his early education was in small private schools where he demonstrated outstanding talent and interest in science. In 1870, he was admitted to Owens College in Manchester at the unusually young age of 14, his parents planned to enroll him as an apprentice engineer to Sharp-Stewart & Co, a locomotive manufacturer, but these plans were cut short when his father died in 1873. He moved on to Trinity College, Cambridge, in 1876. In 1880, he obtained his Bachelor of Arts degree in mathematics, he applied for and became a Fellow of Trinity College in 1881. Thomson received his Master of Arts degree in 1883. In 1890, Thomson married Rose Elisabeth Paget, one of his former students, daughter of Sir George Edward Paget, KCB, a physician and Regius Professor of Physic at Cambridge at the church of St. Mary the Less, they had one son, George Paget Thomson, one daughter, Joan Paget Thomson. On 22 December 1884, Thomson was appointed Cavendish Professor of Physics at the University of Cambridge.
The appointment caused considerable surprise, given that candidates such as Osborne Reynolds or Richard Glazebrook were older and more experienced in laboratory work. Thomson was known for his work as a mathematician, he was awarded a Nobel Prize in 1906, "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases." He was knighted in 1908 and appointed to the Order of Merit in 1912. In 1914, he gave the Romanes Lecture in Oxford on "The atomic theory". In 1918, he became Master of Trinity College, where he remained until his death. Joseph John Thomson died on 30 August 1940. One of Thomson's greatest contributions to modern science was in his role as a gifted teacher. One of his students was Ernest Rutherford, who succeeded him as Cavendish Professor of Physics. In addition to Thomson himself, six of his research assistants won Nobel Prizes in physics, two won Nobel prizes in chemistry. In addition, Thomson's son won the 1937 Nobel Prize in physics for proving the wave-like properties of electrons.
Thomson's prize-winning master's work, Treatise on the motion of vortex rings, shows his early interest in atomic structure. In it, Thomson mathematically described the motions of William Thomson's vortex theory of atoms. Thomson published a number of papers addressing both mathematical and experimental issues of electromagnetism, he examined the electromagnetic theory of light of James Clerk Maxwell, introduced the concept of electromagnetic mass of a charged particle, demonstrated that a moving charged body would increase in mass. Much of his work in mathematical modelling of chemical processes can be thought of as early computational chemistry. In further work, published in book form as Applications of dynamics to physics and chemistry, Thomson addressed the transformation of energy in mathematical and theoretical terms, suggesting that all energy might be kinetic, his next book, Notes on recent researches in electricity and magnetism, built upon Maxwell's Treatise upon electricity and magnetism, was sometimes referred to as "the third volume of Maxwell".
In it, Thomson emphasized physical methods and experimentation and included extensive figures and diagrams of apparatus, including a number for the passage of electricity through gases. His third book, Elements of the mathematical theory of electricity and magnetism was a readable introduction to a wide variety of subjects, achieved considerable popularity as a textbook. A series of four lectures, given by Thomson on a visit to Princeton University in 1896, were subsequently published as Discharge of electricity through gases. Thomson presented a series of six lectures at Yale University in 1904. Several scientists, such as William Prout and Norman Lockyer, had suggested that atoms were built up from a more fundamental unit, but they envisioned this unit to be the size of the smallest atom, hydrogen. Thomson in 1897 was the first to suggest that one of the fundamental units was more than 1,000 times smaller than an atom, suggesting th
Chromatography is a laboratory technique for the separation of a mixture. The mixture is dissolved in a fluid called the mobile phase, which carries it through a structure holding another material called the stationary phase; the various constituents of the mixture travel at different speeds. The separation is based on differential partitioning between the stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus affect the separation. Chromatography may be analytical; the purpose of preparative chromatography is to separate the components of a mixture for use, is thus a form of purification. Analytical chromatography is done with smaller amounts of material and is for establishing the presence or measuring the relative proportions of analytes in a mixture; the two are not mutually exclusive. Chromatography, pronounced, is derived from Greek χρῶμα chroma, which means "color", γράφειν graphein, which means "to write".
Chromatography was first employed in Russia by the Italian-born scientist Mikhail Tsvet in 1900. He continued to work with chromatography in the first decade of the 20th century for the separation of plant pigments such as chlorophyll and xanthophylls. Since these components have different colors they gave the technique its name. New types of chromatography developed during the 1930s and 1940s made the technique useful for many separation processes. Chromatography technique developed as a result of the work of Archer John Porter Martin and Richard Laurence Millington Synge during the 1940s and 1950s, for which they won the 1952 Nobel Prize in Chemistry, they established the principles and basic techniques of partition chromatography, their work encouraged the rapid development of several chromatographic methods: paper chromatography, gas chromatography, what would become known as high-performance liquid chromatography. Since the technology has advanced rapidly. Researchers found that the main principles of Tsvet's chromatography could be applied in many different ways, resulting in the different varieties of chromatography described below.
Advances are continually improving the technical performance of chromatography, allowing the separation of similar molecules. Chromatography has been employed as a method to test the potency of cannabis; the analyte is the substance to be separated during chromatography. It is normally what is needed from the mixture. Analytical chromatography is used to determine the existence and also the concentration of analyte in a sample. A bonded phase is a stationary phase, covalently bonded to the support particles or to the inside wall of the column tubing. A chromatogram is the visual output of the chromatograph. In the case of an optimal separation, different peaks or patterns on the chromatogram correspond to different components of the separated mixture. Plotted on the x-axis is the retention time and plotted on the y-axis a signal corresponding to the response created by the analytes exiting the system. In the case of an optimal system the signal is proportional to the concentration of the specific analyte separated.
A chromatograph is equipment that enables a sophisticated separation, e.g. gas chromatographic or liquid chromatographic separation. Chromatography is a physical method of separation that distributes components to separate between two phases, one stationary, the other moving in a definite direction; the eluate is the mobile phase leaving the column. This is called effluent; the eluent is the solvent. The eluite is the eluted solute. An eluotropic series is a list of solvents ranked according to their eluting power. An immobilized phase is a stationary phase, immobilized on the support particles, or on the inner wall of the column tubing; the mobile phase is the phase. It may be a gas, or a supercritical fluid; the mobile phase consists of the sample being separated/analyzed and the solvent that moves the sample through the column. In the case of HPLC the mobile phase consists of a non-polar solvent such as hexane in normal phase or a polar solvent such as methanol in reverse phase chromatography and the sample being separated.
The mobile phase moves through the chromatography column where the sample interacts with the stationary phase and is separated. Preparative chromatography is used to purify sufficient quantities of a substance for further use, rather than analysis; the retention time is the characteristic time it takes for a particular analyte to pass through the system under set conditions. See also: Kovats' retention index The sample is the matter analyzed in chromatography, it may consist of a single component or it may be a mixture of components. When the sample is treated in the course of an analysis, the phase or the phases containing the analytes of interest is/are referred to as the sample whereas everything out of interest separated from the sample before or in the course of the analysis is referred to as waste; the solute refers to the sample components in partition chromatography. The solvent refers to any substance capable of solubilizing another substance, the liquid mobile phase in liquid chromatography.
The stationary phase is the substance fixed in place for the chromatography procedure. Examples include the silica layer i
The mass-to-charge ratio is a physical quantity, most used in the electrodynamics of charged particles, e.g. in electron optics and ion optics. It appears in the scientific fields of electron microscopy, cathode ray tubes, accelerator physics, nuclear physics, Auger electron spectroscopy and mass spectrometry; the importance of the mass-to-charge ratio, according to classical electrodynamics, is that two particles with the same mass-to-charge ratio move in the same path in a vacuum, when subjected to the same electric and magnetic fields. Its SI units are kg/C. In rare occasions the thomson has been used as its unit in the field of mass spectrometry; some fields use the charge-to-mass ratio instead, the multiplicative inverse of the mass-to-charge ratio. The 2014 CODATA recommended value for an electron is Q⁄m = 1.758820024×1011 C/kg. When charged particles move in electric and magnetic fields the following two laws apply: where F is the force applied to the ion, m is the mass of the particle, a is the acceleration, Q is the electric charge, E is the electric field, v × B is the cross product of the ion's velocity and the magnetic flux density.
This differential equation is the classic equation of motion for charged particles. Together with the particle's initial conditions, it determines the particle's motion in space and time in terms of m/Q, thus mass spectrometers could be thought of as "mass-to-charge spectrometers". When presenting data in a mass spectrum, it is common to use the dimensionless m/z, which denotes the dimensionless quantity formed by dividing the mass number of the ion by its charge number. Combining the two previous equations yields: a = E + v × B; this differential equation is the classic equation of motion of a charged particle in vacuum. Together with the particle's initial conditions it determines the particle's motion in space and time, it reveals that two particles with the same m/Q ratio behave in the same way. This is why the mass-to-charge ratio is an important physical quantity in those scientific fields where charged particles interact with magnetic or electric fields. There are non-classical effects that derive from quantum mechanics, such as the Stern–Gerlach effect that can diverge the path of ions of identical m/Q.
The IUPAC recommended symbol for mass and charge are m and Q however using a lowercase q for charge is very common. Charge is a scalar property, meaning that it can be either negative; the Coulomb is the SI unit of charge. The SI unit of the physical quantity m/Q is kilogram per coulomb; the units and notation above are used. This notation eases data interpretation since it is numerically more related to the unified atomic mass unit; the m refers to z to the charge number of the ion. An ion of 100 atomic mass units carrying two charges will be observed at m/z = 50. In the 19th century, the mass-to-charge ratios of some ions were measured by electrochemical methods. In 1897, the mass-to-charge ratio of the electron was first measured by J. J. Thomson. By doing this, he showed that the electron was in fact a particle with a mass and a charge, that its mass-to-charge ratio was much smaller than that of the hydrogen ion H+. In 1898, Wilhelm Wien separated ions according to their mass-to-charge ratio with an ion optical device with superimposed electric and magnetic fields.
In 1901 Walter Kaufman measured the increase of electromagnetic mass of fast electrons, or relativistic mass increase in modern terms. In 1913, Thomson measured the mass-to-charge ratio of ions with an instrument he called a parabola spectrograph. Today, an instrument that measures the mass-to-charge ratio of charged particles is called a mass spectrometer; the charge-to-mass ratio of an object is, as its name implies, the charge of an object divided by the mass of the same object. This quantity is useful only for objects that may be treated as particles. For extended objects, total charge, charge density, total mass, mass density are more useful. Derivation: q v B = m v v r or q m = v B r Since F e l e c t r i c = F m a g n e t i c, E q = B q v or v = E B Equations and yield q m = E B 2 r In some experiments, the charge-to-mass ratio is the only quantity that can be measured directly; the charge can be inferred from theoretical considerations, so that the char
Fourier-transform ion cyclotron resonance
Fourier-transform ion cyclotron resonance mass spectrometry is a type of mass analyzer for determining the mass-to-charge ratio of ions based on the cyclotron frequency of the ions in a fixed magnetic field. The ions are trapped in a Penning trap, where they are excited to a larger cyclotron radius by an oscillating electric field orthogonal to the magnetic field. After the excitation field is removed, the ions are rotating at their cyclotron frequency in phase; these ions induce a charge on a pair of electrodes. The resulting signal is called a free induction decay, transient or interferogram that consists of a superposition of sine waves; the useful signal is extracted from this data by performing a Fourier transform to give a mass spectrum. FT-ICR was invented by Melvin B. Comisarow and Alan G. Marshall at the University of British Columbia; the first paper appeared in Chemical Physics Letters in 1974. The inspiration was earlier developments in conventional ICR and Fourier-transform nuclear magnetic resonance spectroscopy.
Marshall has continued to develop the technique at The Ohio State University and Florida State University. The physics of FTICR is similar to that of a cyclotron at least in the first approximation. In the simplest idealized form, the relationship between the cyclotron frequency and the mass-to-charge ratio is given by f = q B 2 π m, where f = cyclotron frequency, q = ion charge, B = magnetic field strength and m = ion mass; this is more represented in angular frequency: ω c = q B m, where ω c is the angular cyclotron frequency, related to frequency by the definition f = ω 2 π. Because of the quadrupolar electrical field used to trap the ions in the axial direction, this relationship is only approximate; the axial electrical trapping results in axial oscillations within the trap with the frequency ω t = q α m, where α is a constant similar to the spring constant of a harmonic oscillator and is dependent on applied voltage, trap dimensions and trap geometry. The electric field and the resulting axial harmonic motion reduces the cyclotron frequency and introduces a second radial motion called magnetron motion that occurs at the magnetron frequency.
The cyclotron motion is still the frequency being used, but the relationship above is not exact due to this phenomenon. The natural angular frequencies of motion are ω ± = ω c 2 ± 2 − ω t 2 2, where ω t is the axial trapping frequency due the axial electrical trapping and ω + is the reduced cyclotron frequency and ω − is the magnetron frequency. Again, ω + is what is measured in FTICR; the meaning of this equation can be understood qualitatively by considering the case where ω t is small, true. In that case the value of the radical is just less than ω c / 2, the value of ω + is just less than ω c. For ω − the value of the radical is the same, but it is being subtracted from ω c / 2, resulting in a small number equal to ω c − ω +. FTICR-MS differs from other mass spectrometry techniques in that the ions are not detected by hitting a detector such as an electron multiplier but only by passing near detection plates. Additionally the masses are not resolved in space or time as with other techniques but only by the ion cyclotron resonance frequency that each ion produces as it rotates in a magnetic field.
Thus, the different ions are not detected in different places as with sector instruments or at different times as with time-of-flight instruments, but all ions are detected during the detection inter
Quantities, Units and Symbols in Physical Chemistry
Quantities and Symbols in Physical Chemistry known as the Green Book, is a compilation of terms and symbols used in the field of physical chemistry. It includes a table of physical constants, tables listing the properties of elementary particles, chemical elements, nuclides, information about conversion factors that are used in physical chemistry; the Green Book is published by the International Union of Pure and Applied Chemistry and is based on published, citeable sources. Information in the Green Book is synthesized from recommendations made by IUPAC, the International Union of Pure and Applied Physics and the International Organization for Standardization, including recommendations listed in the IUPAP Red Book Symbols, Units and Fundamental Constants in Physics and in the ISO 31 standards; the third edition of the Green Book was first published by IUPAC in 2007. A second printing of the third edition was released in 2008. A third printing of the third edition was released in 2011; the text of the third printing is identical to that of the second printing.
A Japanese translation of the third edition of the Green Book was published in 2009. A French translation of the third edition of the Green Book was published in 2012. A concise four-page summary of the most important material in the Green Book was published in the July–August 2011 issue of Chemistry International, the IUPAC news magazine; the second edition of the Green Book was first published in 1993. It was reprinted in 1995, 1996, 1998; the Green Book is a direct successor of the Manual of Symbols and Terminology for Physicochemical Quantities and Units prepared for publication on behalf of IUPAC's Physical Chemistry Division by M. L. McGlashen in 1969. A full history of the Green Book's various editions is provided in the historical introduction to the third edition; the second edition and the third edition of the Green Book have both been made available online as PDF files. The four-page concise summary is available online as a PDF file. External Links. In addition to the obvious data on quantities and symbols, the compilation contains some less obvious but useful information on related topics.
Unit conversion is a notorious source of errors. Many people apply individual rules, e.g. "to obtain length in centimeters multiply the length in inches by 2.54", but combining several such conversions is laborious and prone to mistakes. A better way is to use the factor-label method, related to dimensional analysis, quantity calculus explained in sections 1.1 and 7.1 of this compilation. Section 1.3 explains the rules for writing scientific symbols and names, for example, where to use capital letters or italics, where their use is incorrect. No typographical rule seems to be missing such detail as whether "20°C" or "20 °C" is the correct form. Section 3.8 introduces atomic units and gives a table of atomic units of various physical quantities and the conversion factor to the SI units. Section 7.3 gives a concise but clear tutorial on practical use of atomic units, in particular how to understand equations "written in atomic units". Nomenclature of Organic Chemistry Nomenclature of Inorganic Chemistry Compendium of Chemical Terminology Compendium of Analytical Nomenclature Quantities and Symbols in Physical Chemistry, IUPAC Green Book, third edition Concise four-page summary of the Green Book's third edition Second edition of the Green Book IUPAC Nomenclature Books Series IUPAC official website
Whole number rule
The whole number rule states that the masses of the isotopes are whole number multiples of the mass of the hydrogen atom. The rule is a modified version of Prout's hypothesis proposed in 1815, to the effect that atomic weights are multiples of the weight of the hydrogen atom, it is known as the Aston whole number rule after Francis W. Aston, awarded the Nobel Prize in Chemistry in 1922 "for his discovery, by means of his mass spectrograph, of isotopes, in a large number of non-radioactive elements, for his enunciation of the whole-number rule." The law of definite proportions was formulated by Joseph Proust around 1800 and states that all samples of a chemical compound will have the same elemental composition by mass. The atomic theory of John Dalton expanded this concept and explained matter as consisting of discrete atoms with one kind of atom for each element combined in fixed proportions to form compounds. In 1815, William Prout reported on his observation that the atomic weights of the elements were whole multiples of the atomic weight of hydrogen.
He hypothesized that the hydrogen atom was the fundamental object and that the other elements were a combination of different numbers of hydrogen atoms. In 1920, Francis W. Aston demonstrated through the use of a mass spectrometer that apparent deviations from Prout's hypothesis are predominantly due to the existence of isotopes; these deviations are secondarily due to binding energy, as mass defect. During the 1920s, it was thought that the atomic nucleus was made of protons and electrons, which would account for the disparity between the atomic number of an atom and its atomic mass. In 1932, James Chadwick discovered an uncharged particle of the mass as the proton, which he called the neutron; the fact that the atomic nucleus is composed of protons and neutrons was accepted and Chadwick was awarded the Nobel Prize in Physics in 1935 for his discovery. The modern form of the whole number rule is that the atomic mass of a given elemental isotope is the mass number times an atomic mass unit; this rule predicts the atomic mass of nuclides and isotopes with an error of at most 1%.
Harkins WD. "The Separation of Chlorine into Isotopes and the Whole Number Rule for Atomic Weights". Proc. Natl. Acad. Sci. U. S. A. 11: 624–8. Bibcode:1925PNAS...11..624H. Doi:10.1073/pnas.11.10.624. PMC 1086175. PMID 16587053. 1922 Nobel Prize Presentation Speech
In organic chemistry, the tropylium ion or cycloheptatrienyl cation is an aromatic species with a formula of +. Its name derives from the molecule tropine from which cycloheptatriene was first synthesized in 1881. Salts of the tropylium cation can be stable with nucleophiles of moderate strength e.g. tropylium tetrafluoroborate and tropylium bromide. Its bromide and chloride salts can be made from cycloheptatriene and bromine or phosphorus pentachloride, respectively, it is a regular heptagonal, cyclic ion. It can coordinate as a ligand to metal atoms; the structure shown is a composite of seven resonance contributors in which each carbon atom carries part of the positive charge. In 1891 G. Merling obtained a water-soluble bromine containing compound from a reaction of cycloheptatriene and bromine. Unlike most hydrocarbyl bromides, this compound named tropylium bromide, is a water-soluble solid and is insoluble in hydrocarbons and ether, it is purified by crystallization from hot ethanol. Reaction with aqeuous silver nitrate gave a precipitate of silver bromide.
The structure of tropylium bromide was deduced to be a salt, C7H7+Br–, by Doering and Knox in 1954 by analysis of its infrared and ultraviolet spectra. The ionic structures of tropylium perchlorate and tropylium iodide in the solid state have been confirmed by X-ray crystallography; the bond length of the carbon-carbon bonds were found to be longer than those of benzene but still shorter than those of a typical single-bonded species like ethane. The tropylium ion is an acid in aqueous solution as a consequence of its Lewis acidity: it first acts as a Lewis acid to form an adduct with water, which can donate a proton to another molecule of water: C7H7+ + 2H2O ⇌ C7H7OH + H3O+; the equilibrium constant is 1.8 × 10–5, making it about as acidic in water as acetic acid. The tropylium ion is encountered in mass spectrometry in the form of a signal at m/z = 91 and is used in mass spectrum analysis; this fragment is found for aromatic compounds containing a benzyl unit. Upon ionization, the benzyl fragment forms a cation, which rearranges to the stable tropylium cation.
The tropylium cation reacts with nucleophiles to form substituted cycloheptatrienes, for example: C7H+7 + CN− → C7H7CNReduction by lithium aluminum hydride yields cycloheptatriene. Reaction with a cyclopentadienide salt of sodium or lithium yields 7-cyclopentadienylcyclohepta-1,3,5-triene: C7H+7X− + C5H−5Na+ → C7H7C5H5 + NaXWhen treated with oxidising agents such as chromic acid, the tropylium cation undergoes rearrangement into benzaldehyde: C7H+7 + HCrO−4 → C6H5CHO + CrO2 + H2OMany metal complexes of tropylium ion are known. One example is +, prepared by hydride abstraction from cycloheptatrienemolybdenum tricarbonyl. Azulene Borepin