Chemistry is the scientific discipline involved with elements and compounds composed of atoms and ions: their composition, properties and the changes they undergo during a reaction with other substances. In the scope of its subject, chemistry occupies an intermediate position between physics and biology, it is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant chemistry, the formation of igneous rocks, how atmospheric ozone is formed and how environmental pollutants are degraded, the properties of the soil on the moon, how medications work, how to collect DNA evidence at a crime scene. Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron; the word chemistry comes from alchemy, which referred to an earlier set of practices that encompassed elements of chemistry, philosophy, astronomy and medicine.
It is seen as linked to the quest to turn lead or another common starting material into gold, though in ancient times the study encompassed many of the questions of modern chemistry being defined as the study of the composition of waters, growth, disembodying, drawing the spirits from bodies and bonding the spirits within bodies by the early 4th century Greek-Egyptian alchemist Zosimos. An alchemist was called a'chemist' in popular speech, 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; this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, in turn derived from the word Kemet, the ancient name of Egypt in the Egyptian language. Alternately, al-kīmīā may derive from χημεία, meaning "cast together"; the current model of atomic structure is the quantum mechanical model. Traditional chemistry starts with the study of elementary particles, molecules, metals and other aggregates of matter.
This matter can be studied in isolation or in combination. The interactions and transformations that are studied in chemistry are the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together; such behaviors are studied in a chemistry laboratory. The chemistry laboratory stereotypically uses various forms of laboratory glassware; however glassware is not central to chemistry, a great deal of experimental chemistry is done without it. A chemical reaction is a transformation of some substances into one or more different substances; the basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation, which involves atoms as subjects; the number of atoms on the left and the right in the equation for a chemical transformation is equal. The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.
Energy and entropy considerations are invariably important in all chemical studies. Chemical substances are classified in terms of their structure, phase, as well as their chemical compositions, they can be analyzed using the tools of e.g. spectroscopy and chromatography. Scientists engaged in chemical research are known as chemists. Most chemists specialize in one or more sub-disciplines. Several concepts are essential for the study of chemistry; the particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon. Matter can be a mixture of substances; the atom is the basic unit of chemistry. It consists of a dense core called the atomic nucleus surrounded by a space occupied by an electron cloud; the nucleus is made up of positively charged protons and uncharged neutrons, while the electron cloud consists of negatively charged electrons which orbit the nucleus. In a neutral atom, the negatively charged electrons balance out the positive charge of the protons.
The nucleus is dense. The atom is the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state, coordination number, preferred types of bonds to form. A chemical element is a pure substance, composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z; the mass number is the sum of the number of neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same
Myndus or Myndos was an ancient Dorian colony of Troezen, on the coast of Caria in Asia Minor, sited on the Bodrum Peninsula, a few miles northwest of Halicarnassus. The site is now occupied by the modern village of Gümüslük. Myndos was protected by strong walls, had a good harbor. Otherwise, the place is not of much importance in ancient history. Both Pliny and Stephanus of Byzantium mention Palaemyndus as an ancient Carian settlement near to Myndus, which seems to have become deserted after Dorian Mynduse was founded.. Mela and Pliny speak of a place called Neapolis in the same peninsula and as no other authors mention such a place in that part of the country, it has been supposed that Myndus and Neapolis were the same place. Pliny, mentions both Myndus and Neapolis as two different towns; the cynic philosopher Diogenes of Sinope visited Myndos and noticed how large the city gates were, relative to the town. Sections of the town walls and gate have been restored with financial assistance from private companies.
Myndian ships are mentioned in the expedition of Anaxagoras against Naxos. Herodotus relates the story of how a captain from Myndus, was found to have left no guards on his ship while a Persian force was preparing to attack the island of Naxos; the Persian commander, flew into a rage and had him put in stocks, at which point Aristagoras, a tyrant from Miletus helping several Naxian oligarchs to retake Naxos, discovered what had happened to his guest-friend Scylax. Pleading with Megabates to no avail for Scylax, he released him anyway, incurring the Persian commander's wrath; the consequence of this falling out was that, according to Herodotus, Megabates warned the Naxians of what was afoot, ruining the expedition and in turn Aristagoras who, with nowhere to go, stirred up the Ionian Revolt. This is a classic example of Ionian αταξιη, a charge levelled at them in the 5th century by Athens. At a time, when Alexander the Great besieged Halicarnassus, he was anxious first to make himself master of Myndus.
Athenaeus states. Remains of the city are visible around Gümüslük and in the adjacent waters; as a result, much of the land and offshore areas are protected from development. Myndus was an episcopal see of a suffragan of Stauropolis; the Notitiæ episcopatuum allude to it as late as the 13th century. However, only four of its bishops are known: Archelaus; the bishopric is included in the Catholic Church's list of titular sees. This article incorporates text from a publication now in the public domain: Smith, William, ed.. "article name needed". Dictionary of Greek and Roman Geography. London: John Murray. Gumusluk Gümüslük
Michael J. S. Dewar
Michael James Steuart Dewar was a theoretical chemist. Dewar was the son of Annie Balfour and Francis Dewar, he received the degrees of Bachelor of Arts, Master of Arts, DPhil from Balliol College, Oxford. Dewar was appointed to the Chair in Chemistry at Queen Mary College of the University of London in 1951, he moved to the University of Chicago in 1959 and to the first Robert A. Welch research chair at the University of Texas at Austin in 1963. After a long and productive period there, he moved to the University of Florida in 1989, he retired in 1994 as Professor Emeritus at the University of Florida. He died in 1997. Dewar's reputation for providing original solutions to vexing puzzles first developed when he was still a postdoctoral fellow at the University of Oxford. In 1945, he deduced the correct structure for stipitatic acid, a mould product whose structure had baffled the leading chemists of the day, it involved a new kind of aromatic structure with a seven-membered ring for which Dewar coined the term tropolone.
The discovery of the tropolone structure launched the field of non-benzenoid aromaticity, which witnessed feverish activity for several decades and expanded the chemists' understanding of cyclic π-electron systems. In 1945, Dewar devised the novel notion of a π complex, which he proposed as an intermediate in the benzidine rearrangement; this offered the first correct rationalisation of the electronic structure of complexes of transition metals with alkenes known as the Dewar-Chatt-Duncanson model. In the early 1950s, Dewar wrote a famous series of six articles on a general Molecular orbital Theory of Organic Chemistry, which extended and generalised Erich Hückel's original quantum mechanical treatments by using perturbation theory and resonance theory, which in many ways originated the modern era of theoretical and computational organic chemistry. Following Woodward and Hoffmann's suggestion of selection rules for pericyclic reactions, Dewar championed an alternative approach to understanding pericyclic reactivity based on aromatic and antiaromatic transition states.
He did not however believe in the utility of Möbius aromaticity, introduced by Edgar Heilbronner in 1964, now a flourishing area of chemistry. He is known most famously for the development in the 1970s and 1980s of the Semi-empirical quantum chemistry methods, MINDO, MNDO, AM1 and PM3 that are in the MOPAC computer program, which for the first time enabled the quantitative study of the structure and mechanism of reaction of many real systems; this was illustrated in 1974 by computing the structure of a molecule as large as LSD at a quantum mechanical level. It is worth noting that in 2006, the equivalent calculation takes less than 1 minute on a personal computer. In 2006, the same structure computation can now be completed using high-level ab initio or density functional procedures in less than two days, semiempirical programs can be used to optimise the structures of molecules with 10,000 atoms, he was a member of the International Academy of Quantum Molecular Science. His accolades include: Fellow of the American Academy of Sciences.
W. Wheland Medal of the University of Chicago. M. Kosolapoff Award of the American Chemical Society, he is the father of Robert Dewar and Steuart Dewar
Mindo is a mountainous watershed in the western slopes of the Andes, where two of the most biologically diverse ecoregions in the world meet: the Chocoan lowlands and the Tropical Andes. In this transitional area — which covers an area of 268 square kilometers and ranges from 960–3,440 metres above sea level — three rivers and hundreds of streams irrigate the landscape, a patchwork of cloud forests, secondary forests, agricultural land, human settlements. Politically, Mindo is a collection of rural parishes that make up the Noroccidental Administrative Zone of Quito Canton, within Pichincha Province in the northern sierra region of Ecuador; the Mindo Valley is among the most visited tourist locations in Ecuador. Mindo was named the Ruta de Cacao by The Ecuadorian Ministerio de Turismo. Nearly 200,000 tourists visit the area annually to enjoy activities such as rafting, trekking, mountain biking, horseback riding, Chocolate Making and herping. Besides its well-developed tourism infrastructure, it offers several private reserves and lodges known for their montane forests and unique cloud forest biodiversity.
Much of the land is protected, an additional 86 square kilometers falls within the Mindo-Nambillo Ecological Reserve. Mindo travel guide from Wikivoyage
Quantum mechanics, including quantum field theory, is a fundamental theory in physics which describes nature at the smallest scales of energy levels of atoms and subatomic particles. Classical physics, the physics existing before quantum mechanics, describes nature at ordinary scale. Most theories in classical physics can be derived from quantum mechanics as an approximation valid at large scale. Quantum mechanics differs from classical physics in that energy, angular momentum and other quantities of a bound system are restricted to discrete values. Quantum mechanics arose from theories to explain observations which could not be reconciled with classical physics, such as Max Planck's solution in 1900 to the black-body radiation problem, from the correspondence between energy and frequency in Albert Einstein's 1905 paper which explained the photoelectric effect. Early quantum theory was profoundly re-conceived in the mid-1920s by Erwin Schrödinger, Werner Heisenberg, Max Born and others; the modern theory is formulated in various specially developed mathematical formalisms.
In one of them, a mathematical function, the wave function, provides information about the probability amplitude of position and other physical properties of a particle. Important applications of quantum theory include quantum chemistry, quantum optics, quantum computing, superconducting magnets, light-emitting diodes, the laser, the transistor and semiconductors such as the microprocessor and research imaging such as magnetic resonance imaging and electron microscopy. Explanations for many biological and physical phenomena are rooted in the nature of the chemical bond, most notably the macro-molecule DNA. Scientific inquiry into the wave nature of light began in the 17th and 18th centuries, when scientists such as Robert Hooke, Christiaan Huygens and Leonhard Euler proposed a wave theory of light based on experimental observations. In 1803, Thomas Young, an English polymath, performed the famous double-slit experiment that he described in a paper titled On the nature of light and colours.
This experiment played a major role in the general acceptance of the wave theory of light. In 1838, Michael Faraday discovered cathode rays; these studies were followed by the 1859 statement of the black-body radiation problem by Gustav Kirchhoff, the 1877 suggestion by Ludwig Boltzmann that the energy states of a physical system can be discrete, the 1900 quantum hypothesis of Max Planck. Planck's hypothesis that energy is radiated and absorbed in discrete "quanta" matched the observed patterns of black-body radiation. In 1896, Wilhelm Wien empirically determined a distribution law of black-body radiation, known as Wien's law in his honor. Ludwig Boltzmann independently arrived at this result by considerations of Maxwell's equations. However, it underestimated the radiance at low frequencies. Planck corrected this model using Boltzmann's statistical interpretation of thermodynamics and proposed what is now called Planck's law, which led to the development of quantum mechanics. Following Max Planck's solution in 1900 to the black-body radiation problem, Albert Einstein offered a quantum-based theory to explain the photoelectric effect.
Around 1900–1910, the atomic theory and the corpuscular theory of light first came to be accepted as scientific fact. Among the first to study quantum phenomena in nature were Arthur Compton, C. V. Raman, Pieter Zeeman, each of whom has a quantum effect named after him. Robert Andrews Millikan studied the photoelectric effect experimentally, Albert Einstein developed a theory for it. At the same time, Ernest Rutherford experimentally discovered the nuclear model of the atom, for which Niels Bohr developed his theory of the atomic structure, confirmed by the experiments of Henry Moseley. In 1913, Peter Debye extended Niels Bohr's theory of atomic structure, introducing elliptical orbits, a concept introduced by Arnold Sommerfeld; this phase is known as old quantum theory. According to Planck, each energy element is proportional to its frequency: E = h ν, where h is Planck's constant. Planck cautiously insisted that this was an aspect of the processes of absorption and emission of radiation and had nothing to do with the physical reality of the radiation itself.
In fact, he considered his quantum hypothesis a mathematical trick to get the right answer rather than a sizable discovery. However, in 1905 Albert Einstein interpreted Planck's quantum hypothesis realistically and used it to explain the photoelectric effect, in which shining light on certain materials can eject electrons from the material, he won the 1921 Nobel Prize in Physics for this work. Einstein further developed this idea to show that an electromagnetic wave such as light could be described as a particle, with a discrete quantum of energy, dependent on its frequency; the foundations of quantum mechanics were established during the first half of the 20th century by Max Planck, Niels Bohr, Werner Heisenberg, Louis de Broglie, Arthur Compton, Albert Einstein, Erwin Schrödinger, Max Born, John von Neumann, Paul Dirac, Enrico Fermi, Wolfgang Pauli, Max von Laue, Freeman Dyson, David Hilbert, Wi
Computational chemistry is a branch of chemistry that uses computer simulation to assist in solving chemical problems. It uses methods of theoretical chemistry, incorporated into efficient computer programs, to calculate the structures and properties of molecules and solids, it is necessary because, apart from recent results concerning the hydrogen molecular ion, the quantum many-body problem cannot be solved analytically, much less in closed form. While computational results complement the information obtained by chemical experiments, it can in some cases predict hitherto unobserved chemical phenomena, it is used in the design of new drugs and materials. Examples of such properties are structure and relative energies, electronic charge density distributions and higher multipole moments, vibrational frequencies, reactivity, or other spectroscopic quantities, cross sections for collision with other particles; the methods used cover both dynamic situations. In all cases, the computer time and other resources increase with the size of the system being studied.
That system can be a group of molecules, or a solid. Computational chemistry methods range from approximate to accurate. Ab initio methods are based on quantum mechanics and basic physical constants. Other methods are called empirical or semi-empirical because they use additional empirical parameters. Both ab initio and semi-empirical approaches involve approximations; these range from simplified forms of the first-principles equations that are easier or faster to solve, to approximations limiting the size of the system, to fundamental approximations to the underlying equations that are required to achieve any solution to them at all. For example, most ab initio calculations make the Born–Oppenheimer approximation, which simplifies the underlying Schrödinger equation by assuming that the nuclei remain in place during the calculation. In principle, ab initio methods converge to the exact solution of the underlying equations as the number of approximations is reduced. In practice, however, it is impossible to eliminate all approximations, residual error remains.
The goal of computational chemistry is to minimize this residual error while keeping the calculations tractable. In some cases, the details of electronic structure are less important than the long-time phase space behavior of molecules; this is the case in conformational studies of protein-ligand binding thermodynamics. Classical approximations to the potential energy surface are used, as they are computationally less intensive than electronic calculations, to enable longer simulations of molecular dynamics. Furthermore, cheminformatics uses more empirical methods like machine learning based on physicochemical properties. One typical problem in cheminformatics is to predict the binding affinity of drug molecules to a given target. Building on the founding discoveries and theories in the history of quantum mechanics, the first theoretical calculations in chemistry were those of Walter Heitler and Fritz London in 1927; the books that were influential in the early development of computational quantum chemistry include Linus Pauling and E. Bright Wilson's 1935 Introduction to Quantum Mechanics – with Applications to Chemistry, Eyring and Kimball's 1944 Quantum Chemistry, Heitler's 1945 Elementary Wave Mechanics – with Applications to Quantum Chemistry, Coulson's 1952 textbook Valence, each of which served as primary references for chemists in the decades to follow.
With the development of efficient computer technology in the 1940s, the solutions of elaborate wave equations for complex atomic systems began to be a realizable objective. In the early 1950s, the first semi-empirical atomic orbital calculations were performed. Theoretical chemists became extensive users of the early digital computers. One major advance came with the 1951 paper in Reviews of Modern Physics by Clemens C. J. Roothaan in 1951 on the "LCAO MO" approach, for many years the second-most cited paper in that journal. A detailed account of such use in the United Kingdom is given by Smith and Sutcliffe; the first ab initio Hartree–Fock method calculations on diatomic molecules were performed in 1956 at MIT, using a basis set of Slater orbitals. For diatomic molecules, a systematic study using a minimum basis set and the first calculation with a larger basis set were published by Ransil and Nesbet in 1960; the first polyatomic calculations using Gaussian orbitals were performed in the late 1950s.
The first configuration interaction calculations were performed in Cambridge on the EDSAC computer in the 1950s using Gaussian orbitals by Boys and coworkers. By 1971, when a bibliography of ab initio calculations was published, the largest molecules included were naphthalene and azulene. Abstracts of many earlier developments in ab initio theory have been published by Schaefer. In 1964, Hückel method calculations of molecules, ranging in complexity from butadiene and benzene to ovalene, were generated on computers at Berkeley and Oxford; these empirical methods were replaced in the 1960s by semi-empirical methods such as CNDO. In the early 1970s, efficient ab initio computer programs such as ATMOL, Gaussian