Atomic Theory Timeline

By mat0880
  • Antoine Lavoiser

    Antoine Lavoiser
    Lavoisier demonstrated the role of oxygen in the rusting of metal, as well as oxygen's role in animal and plant respiration. Working with Pierre-Simon Laplace, Lavoisier conducted experiments that showed that respiration was essentially a slow combustion of organic material using inhaled oxygen. Lavoisier's explanation of combustion disproved the phlogiston theory, which postulated that materials released a substance called phlogiston when they burned.
  • Democritus

    Democritus, known in antiquity as the ‘laughing philosopher’ because of his emphasis on the value of ‘cheerfulness,’ was one of the two founders of ancient atomist theory. He elaborated a system originated by his teacher Leucippus into a materialist account of the natural world. The atomists held that there are smallest indivisible bodies from which everything else is composed, and that these move about in an infinite void space. Of the ancient materialist accounts of the natural world which did
  • John Dalton

    John Dalton
    In 1800, Dalton became a secretary of the Manchester Literary and Philosophical Society, and in the following year he orally presented an important series of papers, entitled "Experimental Essays" on the constitution of mixed gases; on the pressure of steam and other vapours at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases. These four essays were published in the Memoirs of the Lit & Phil in 1802.
  • Bohr Planetary Model

    Bohr Planetary Model
    In the Bohr Model the neutrons and protons (symbolized by red and blue balls in the adjacent image) occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun (but the orbits are not confined to a plane as is approximately true in the Solar System).
  • Law of Conseravtion of Mass

    Law of Conseravtion of Mass
    The law of conservation of mass, also known as the principle of mass/matter conservation, states that the mass of an isolated system (closed to all transfers of matter and energy) will remain constant over time
  • Dalton's Atmoic Theory

    Dalton's Atmoic Theory
    Modern atomic theory is, of course, a little more involved than Dalton's theory but the essence of Dalton's theory remains valid. Today we know that atoms can be destroyed via nuclear reactions but not by chemical reactions. Also, there are different kinds of atoms (differing by their masses) within an element that are known as "isotopes", but isotopes of an element have the same chemical properties.
  • Quantum Mechanical Model

    Quantum Mechanical Model
    . The quantum mechanical model is based on mathematics. Although it is more difficult to understand than the Bohr model, it can be used to explain observations made on complex atoms.
  • Dmitri Mendeleev

    Dmitri Mendeleev
    In 1863 there were 56 known elements with a new element being discovered at a rate of approximately one per year. Other scientists had previously identified periodicity of elements. John Newlands described a Law of Octaves, noting their periodicity according to relative atomic weight in 1864, publishing it in 1865. His proposal identified the potential for new elements such as germanium. The concept was criticized and his innovation was not recognised by the Society of Chemists until 1887. Anot
  • James Chadwick

    James Chadwick
    Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge. In contrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements.
  • J.J. Thomson

    J.J. Thomson
    Thomson, in 1897, was the first to suggest that the fundamental unit was over 1000 times smaller than an atom, suggesting the subatomic particles now known as electrons. Thomson discovered this through his explorations on the properties of cathode rays. Thomson made his suggestion on 30 April 1897 following his discovery that Lenard rays could travel much further through air than expected for an atom-sized particle.
  • Electron Cloud Model

    Electron Cloud Model
    The electron cloud model is an atom model wherein electrons are no longer depicted as particles moving around the nucleus in a fixed orbit. Instead, as a quantum mechanically-influenced model, we shouldn’t know exactly where they are, and hence describe their probable location around the nucleus only as an arbitrary ‘cloud’.
  • Robert Millikan

    Robert Millikan
    Starting in 1908, while a professor at the University of Chicago, Millikan worked on an oil-drop experiment in which he measured the charge on a single electron. J.J. Thomson had already discovered the charge-to-mass ratio of the electron.
  • Gold Foil Expirenment

    Gold Foil Expirenment
    Before Ernest Rutherford's landmark experiment with a few pieces of metal foil and alpha particles, the structure of the atom was thought to correspond with the plum pudding model. In summary, the plum pudding model was hypothesized by J.J. Thomson (the discoverer of the electron) who described an atom as being a large positively charged body that contained small, free-floating, negatively charged particles called electrons. The plum pudding model also states that the negative charge of the elec
  • Ernest Rutherford

    Ernest Rutherford
    In early work he discovered the concept of radioactive half-life, proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation,proving that the former was essentially helium ions. This work was done at McGill University in Canada. It is the basis for the Nobel Prize in Chemistry he was awarded in 1908 "for his investigations into the disintegration of the elements, and the chemistry of radioactive substanc
  • Rutherford Model

    Rutherford Model
    Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny, massive nucleus. Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structur
  • Plum Pudding Atomic Model

    Plum Pudding Atomic Model
    The plum pudding model of the atom by J. J. Thomson, who discovered the electron in 1897, was proposed in 1904 before the discovery of the atomic nucleus in order to add the electron to the atomic model. In this model, the atom is composed of electrons (which Thomson still called "corpuscles", though G. J. Stoney had proposed that atoms of electricity be called electrons in 1894[1]) surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "plum
  • Henry Moseley

    Henry Moseley
    In 1913, Moseley observed and measured the X-ray spectra of various chemical elements (mostly metals) that were found by the method of diffraction through crystals. This was a pioneering use of the method of X-ray spectroscopy in physics, using Bragg's diffraction law to determine the X-ray wavelengths. Moseley discovered a systematic mathematical relationship between the wavelengths of the X-rays produced and the atomic numbers of the metals that were used as the targets in X-ray tubes. This h
  • Niels Bohr

    Niels Bohr
    n 1922, Bohr was awarded the Nobel Prize in physics "for his services in the investigation of the structure of atoms and of the radiation emanating from them."[13] The award recognized his early leading work in the emerging field of quantum mechanics.
  • Erwin Schrodinger

    Erwin Schrodinger
    In January 1926, Schrödinger published in Annalen der Physik the paper "Quantisierung als Eigenwertproblem" [tr. Quantization as an Eigenvalue Problem] on wave mechanics and presented what is now known as the Schrödinger equation.
  • Cathode Ray Tube

    Cathode Ray Tube
    The cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons or electron emitter) and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images