Atomic Theory

Antione Lavoisier Discovers Oxygen and Gives Modern Chemistry its Nomenclature

Jan 1, 1789

Repeating the experiments of Priestley, he demonstrated that air is composed of two parts, one of which combines with metals to form calxes. However, he tried to take credit for Priestley's discovery. This tendency to use the results of others without acknowledgment then draw conclusions was characteristic of Lavoisier. In Considérations Générales sur la Nature des Acides (1778), he demonstrated that the "air" responsible for combustion was also the source of acidity. The next year, he named this portion oxygen (Greek for acid-former), and the other azote (Greek for no life). He also discovered that the inflammable air of Cavendish which he termed hydrogen (Greek for water-former), combined with oxygen to produce a dew, as Priestley had reported, which appeared to be water.In Reflexions sur le Phlogistique (1783), Lavoisier showed the phlogiston theory to be inconsistent. In Methods of Chemical Nomenclature (1787), he invented the system of chemical nomenclature still largely in use today, including names such as sulfuric acid, sulfates, and sulfites. His Traité Élémentaire de Chimie (Elementary Treatise of Chemistry, 1789) was the first modern chemical textbook, and presented a unified view of new theories of chemistry, contained a clear statement of the Law of Conservation of Mass, and denied the existence of phlogiston. In addition, it contained a list of elements, or substances that could not be broken down further, which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc, and sulfur. His list, however, also included light, and caloric, which he believed to be material substances. In the work, Lavoisier underscored the observational basis of his chemistry, stating "I have tried...to arrive at the truth by linking up facts; to suppress as much as possible the use of reasoning, which is often an unreliable instrument which deceives us, in order to follow as much as possible the torch of observation and of experiment." Nevertheless, he believed that the real existence of atoms was philosophically impossible. Lavoisier demonstrated that organisms disassemble and reconstitute atmospheric air in the same manner as a burning body.

Thomas Young

Jan 1, 1801

In 1801, Young began a series of experiments that addressed a phenomenon known as interference. He observed that when light from a single source is separated into two beams, and the two beams are recombined, the combined beams produce a pattern of light and dark fringes. Young concluded that these fringes were the result of the beams of light behaving as waves with their peaks and troughs either reinforcing one another or canceling each other. When this occurred, alternating lines of light and dark resulted.

J. L. Proust

Jan 1, 1810

He analytically studied the two tin oxides and the two iron sulfides, proving that had different compositions and that there were no substances with intermediate composition.

John Dalton's Discoveries of Basic Molecules

Jan 1, 1827

English meteorologist who switched to chemistry when he saw the applications for chemistry of his ideas about the atmosphere. He proposed the Atomic Theory in 1803 which stated that (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). Dalton's theory was presented in New System of Chemical Philosophy (1808-1827). This work identified chemical elements as a specific type of atom, therefore rejecting Newton's theory of chemical affinities.Instead, Dalton inferred proportions of elements in compounds by taking ratios of the weights of reactants, setting the atomic weight of hydrogen to be identically one. Following Richter, he proposed that chemical elements combine in integral ratios. Despite the importance of the work as the first view of atoms as physically real entities and introduction of a system of chemical symbols, New System of Chemical Philosophy devoted almost as much space to the caloric theory as to atomism.

Heinrich Hertz Tests Maxwell's Hypothesis in 1887

Jan 1, 1887

In 1887 Hertz tested Maxwell's hypothesis. He used an oscillator made of polished brass knobs, each connected to an induction coil and separated by a tiny gap over which sparks could leap. Hertz reasoned that, if Maxwell's predictions were correct, electromagnetic waves would be transmitted during each series of sparks.To confirm this, Hertz made a simple receiver of looped wire. At the ends of the loop were small knobs separated by a tiny gap. The receiver was placed several yards from the oscillator. According to theory, if electromagnetic waves were spreading from the oscillator sparks, they would induce a current in the loop that would send sparks across the gap. This occurred when Hertz turned on the oscillator, producing the first transmission and reception of electromagnetic waves. Hertz also noted that electrical conductors reflect the waves and that they can be focused by concave reflectors. He found that nonconductors allow most of the waves to pass through. Another of his discoveries was the photoelectric effect.

Marie and Pierre Curie Win the Nobel Prize in Physics

Jan 1, 1903

Curie's studies of radioactive substances were made together with his wife, whom he married in 1895. They were achieved under conditions of much hardship - barely adequate laboratory facilities and under the stress of having to do much teaching in order to earn their livelihood. They announced the discovery of radium and polonium by fractionation of pitchblende in 1898 and later they did much to elucidate the properties of radium and its transformation products.

J. J. Thomson Wins the Nobel Prize in Physics

Jan 1, 1906

Thomson returned to America in 1904 to deliver six lectures on electricity and matter at Yale University. They contained some important suggestions as to the structure of the atom. He discovered a method for separating different kinds of atoms and molecules by the use of positive rays, an idea developed by Aston, Dempster and others towards the discovery of many isotopes.

Discoveries of Ernest Marsden

Period: Jan 1, 1907 to Dec 31, 1911

In 1907, under Ernest Rutherford’s influence, Marsden became interested in radioactivity. His most important research work was done as an undergraduate in Rutherford’s department at the University of Manchester. Assisting Hans Geiger by counting α particles fired down a glass tube, he found that they were diffusely reflected from the tube walls. On Rutherford’s suggestion he found that a particles are scattered through large angles from a metal surface, the scattering varying with the atomic weight of the metal. From these results (1909) Rutherford conceived the nuclear theory of atomic structure (1911).

Ernest Rutherford Wins the Nobel Prize in Chemistry

Jan 1, 1908

At Manchester, Rutherford continued his research on the properties of the radium emanation and of the alpha rays and, in conjunction with H. Geiger, a method of detecting a single alpha particle and counting the number emitted from radium was devised. In 1910, his investigations into the scattering of alpha rays and the nature of the inner structure of the atom which caused such scattering led to the postulation of his concept of the "nucleus", his greatest contribution to physics. According to him practically the whole mass of the atom and at the same time all positive charge of the atom is concentrated in a minute space at the centre. In 1912 Niels Bohr joined him at Manchester and he adapted Rutherford's nuclear structure to Max Planck's quantum theory and so obtained a theory of atomic structure which, with later improvements, mainly as a result of Heisenberg's concepts, remains valid to this day. In 1913, together with H. G. Moseley, he used cathode rays to bombard atoms of various elements and showed that the inner structures correspond with a group of lines which characterize the elements. Each element could then be assigned an atomic number and, more important, the properties of each element could be defined by this number. In 1919, during his last year at Manchester, he discovered that the nuclei of certain light elements, such as nitrogen, could be "disintegrated" by the impact of energetic alpha particles coming from some radioactive source, and that during this process fast protons were emitted. Blackett later proved, with the cloud chamber, that the nitrogen in this process was actually transformed into an oxygen isotope, so that Rutherford was the first to deliberately transmute one element into another. G. de Hevesy was also one of Rutherford's collaborators at Manchester.

Niels Bohr Creates the Bohr Model

Jan 1, 1913

By introducing conceptions borrowed from the Quantum Theory as established by Planck, which had gradually come to occupy a prominent position in the science of theoretical physics, he succeeded in working out and presenting a picture of atomic structure that, with later improvements (mainly as a result of Heisenberg's ideas in 1925), still fitly serves as an elucidation of the physical and chemical properties of the elements.

Max Planck Wins the Nobel Prize in Physics

Jan 1, 1918

Planck's earliest work was on the subject of thermodynamics, an interest he acquired from his studies under Kirchhoff, whom he greatly admired, and very considerably from reading R. Clausius' publications. He published papers on entropy, on thermoelectric ity and on the theory of dilute solutions.

Albert Einstein Win the Nobel Prize in Physics

Jan 1, 1921

At the start of his scientific work, Einstein realized the inadequacies of Newtonian mechanics and his special theory of relativity stemmed from an attempt to reconcile the laws of mechanics with the laws of the electromagnetic field. He dealt with classical problems of statistical mechanics and problems in which they were merged with quantum theory: this led to an explanation of the Brownian movement of molecules. He investigated the thermal properties of light with a low radiation density and his observations laid the foundation of the photon theory of light.In his early days in Berlin, Einstein postulated that the correct interpretation of the special theory of relativity must also furnish a theory of gravitation and in 1916 he published his paper on the general theory of relativity. During this time he also contributed to the problems of the theory of radiation and statistical mechanics.

Arthur H. Compton deos the Plum Pudding Experiment

Jan 1, 1922

In his early days at Princeton, Compton devised an elegant method for demonstrating the Earth's rotation, but he was soon to begin his studies in the field of X-rays. He developed a theory of the intensity of X-ray reflection from crystals as a means of studying the arrangement of electrons and atoms, and in 1918 he started a study of X-ray scattering. This led, in 1922, to his discovery of the increase of wavelength of X-rays due to scattering of the incident radiation by free electrons, which implies that the scattered quanta have less energy than the quanta of the original beam.

Niels Bohr Wins the Nobel Prize in Physics

Jan 1, 1922

Louie de Broglie Discovers Wave Mechanics

Jan 1, 1927

This thesis contained a series of important findings which he had obtained in the course of about two years. The ideas set out in that work, which first gave rise to astonishment owing to their novelty, were subsequently fully confirmed by the discovery of electron diffraction by crystals in 1927 by Davisson and Germer; they served as the basis for developing the general theory nowadays known by the name of wave mechanics, a theory which has utterly transformed our knowledge of physical phenomena on the atomic scale.

Arthur H. Compton Wins the Nobel Pize in Physics

Jan 1, 1927

Hans Geiger Invents the Geiger Counter

Jan 1, 1928

When Geiger returned to Germany in 1912 and was appointed as head of the Physikalische Technische Reichsanstalt in Berlin. He continued to work in the field of atomic research and in 1928 he produced an instrument that could detect and count alpha particles called the Geiger Counter.

Louis de Broglie Wins the Nobel Prize in Physics

Jan 1, 1929

Carl D. Anderson's Discoveries

Period: Jan 1, 1930 to Dec 31, 1933

For his doctoral thesis he studied the space distribution of photoelectrons ejected from various gases by X-rays. In 1930, with Professor Millikan, he began his cosmic-ray studies which led in 1932 to the discovery of the positron.

James Chadwick Discovers Neutrons

Jan 1, 1932

In 1932, Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge.

Werner Heisenberg Wins the Nobel Prize in Physics

Jan 1, 1932

Heisenberg's name will always be associated with his theory of quantum mechanics, published in 1925, when he was only 23 years old. For this theory and the applications of it which resulted especially in the discovery of allotropic forms of hydrogen, Heisenberg was awarded the Nobel Prize for Physics for 1932.

Erwin Schrödinger Wins the Nobel Prize in Physics

Jan 1, 1933

It came as a result of his dissatisfaction with the quantum condition in Bohr's orbit theory and his belief that atomic spectra should really be determined by some kind of eigenvalue problem. For this work he shared with Dirac the Nobel Prize for 1933.

Paul A. M. Dirac Wins the Nobel Prize in Physics

Jan 1, 1933

Dirac's work has been concerned with the mathematical and theoretical aspects of quantum mechanics. He began work on the new quantum mechanics as soon as it was introduced by Heisenberg in 1925 - independently producing a mathematical equivalent which consisted essentially of a noncommutative algebra for calculating atomic properties - and wrote a series of papers on the subject, published mainly in the Proceedings of the Royal Society, leading up to his relativistic theory of the electron (1928) and the theory of holes (1930). This latter theory required the existence of a positive particle having the same mass and charge as the known (negative) electron. This, the positron was discovered experimentally at a later date (1932) by C. D. Anderson, while its existence was likewise proved by Blackett and Occhialini (1933 ) in the phenomena of "pair production" and "annihilation".

Irene Joliet-Curie and Artificial Radioactivity

Jan 1, 1934

In 1926 she married Frédéric Joliot ... and there began a collaboration of husband and wife in scientific work rivalling in productive genius even that of her parents. The most outstanding of their joint papers were published in the years 1932-1934. In the first of these, on the radiation excited in beryllium by alpha-particles, they reported a very strange effect which provided the clue to the discovery of the neutron. Then, after studying the conditions of excitation of neutrons by the impact of alpha-particles on various elements, they turned for a time to the 'materialization' of positive electrons through the action of gamma-rays of high energy. This was followed by a systematic study of the radiations emitted from the lighter chemical elements under the impact of alpha-particles, which through the light of intuition -- and good technique -- led them, in early 1934, to their beautiful discovery of artificial radioactivity. An interesting feature of this discovery is that it was so long in coming; for the phenomenon of artificial activity had been expected, and sought for, since the earliest days of radioactivity.

James Chadwick Wins the Nobel Prize

Jan 1, 1935

Carl Anderson Wins the Nobel Prize

Jan 1, 1936

In 1936, Carl D. Anderson won the Nobel Prize in Physics.

Enrico Fermi Wins the Nobel Prize in Physics

Jan 1, 1938

In 1926, Fermi discovered the statistical laws, nowadays known as the «Fermi statistics», governing the particles subject to Pauli's exclusion principle (now referred to as «fermions», in contrast with «bosons» which obey the Bose-Einstein statistics).

Lise Meitner, Otto Hahn, and Fritz Strasmann

Jan 1, 1938

Strassman helped develop the rubidium-strontium method of dating used in geochronology. He joined Otto Hahn and Lise Meitner at the Kaiser Wilhelm Institute for Chemistry and in 1938 discovered that uranium nuclei split when bombarded with neutrons.At the end of 1907, Dr. Lise Meitner came to Berlin from Vienna and then began more than thirty years' collaboration. Their joint work embraced: investigations on beta-rays, their absorbability, magnetic spectra, etc.; use of the radioactive recoil, discovered shortly before by Hahn, to obtain new radioactive transformation products.In 1923, Meitner discovered the radiationless transition known as the Auger effect, which is named for Pierre Victor Auger, a French scientist who discovered the effect two years later.

Otto Frisch Theorizes the Power of Uranium Fission

Jan 1, 1939

In 1939 Frisch wrote a paper with his aunt, Lise Meitner, explaining the theory of uranium fission. In the paper they argued that by splitting the atom it was possible to use a few pounds of uranium to create the explosive and destructive power of many thousands of pounds of dynamite.

Wolfgang Pauli Wins the Nobel Prize in Physics

Jan 1, 1945

Pauli helped to lay the foundations of the quantum theory of fields and he participated actively in the great advances made in this domain around 1945. Earlier, he had further consolidated field theory by giving proof of the relationship between spin and"statistics" of elementary particles.

Richard Feynman and Julain Schwinger Win the Nobel Prize in Physics

Jan 1, 1965

More scientific influences were also at work. He first approached electromagnetic radar problems as a nuclear physicist, but soon began to think of nuclear physics in the language of electrical engineering. That would eventually emerge as the effective range formulation of nuclear scattering. Then, being conscious of the large microwave powers available, Schwinger began to think about electron accelerators, which led to the question of radiation by electrons in magnetic fields.

Murray Gell-Mann and Geirge Zweig Discover

Jan 1, 1969

American physicist who was a graduate student in physics at Caltech under Richard Feynman. Zweig pored over all the experimental data on known particles and proposed the existence of quarks independently of Gell-Mann and Ne'eman. Zweig continued to work in particle physics, both experimental and theoretical, as a professor at Caltech until the early 1970s.In this period he developed the strangeness theory and the eightfold way theory.