Atomic Theory Timeline

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    Democritus (B.C)

    Democritus (B.C)
    Democritus was known as "The father of the atom" and belived that atoms were invisible and indestructible.
    His ideas agreed with later scientific theory , but they did not explain chemical behavior.
  • Johann Becher

    Johann Becher
    Becher and George Stahl(1660-1734) developed the Phlogiston theory which dominated chemistry between 1670 and 1790.
    The idea was when something burned, it lost phlogiston to the air. The problem witht he theory was that burning of metals resulted in an increase in the mass.
    The problem was resolved by assigning mass to Phlogiston.
  • Isaac Newton

    Isaac Newton
    Idea/experiment: Newton formulated a theory of light , three laws of motion and suggested a mechanical universe with small solid masses in motion. He also suggested that atoms are held together with attraction, known as forces.
  • Antoine Lavoisier

    Antoine Lavoisier
    -First person to make good use of the balance.
    After a visit with pristely in 1774, he began studying the burning process.
    Lavoisier proposed the Combustion theory: which was based on sounds mass.
    **He proposed the Law of Conservation of mass.(represents the beginning of Chemistry.) The Law of Conservation of Mass is a relation stating that in a chemical reaction , the mass of the products equals the mass of the reactants .
    -He named Oxygen
  • Amadeo Avogrado

    Amadeo Avogrado
    (1776-1856) Education:Univers. of Turnin
    *Proposed what is now known as "Avagrado's Hypothesis" in 1811,The hypothesis states: at the same temperature and pressure, equal volumes of gases contain the same number of molecules and atoms.
    -His theory combined with Gay Lussacs law of combining volumes , possibke formulas of hydrogen , oxygen and water(H2, O2 and H2O)
    *Avogrados hypothesis was a radical statement and at the time not accepted unitl 50 years later.
  • Joseph Proust

    Joseph Proust
    **Proposed the Law of Constant composition in 1779:n any particular chemical compound, all samples of that compound will be made up of the same elements in the same proportion or ratio. This law was very radical at the time and was contested by Claude Bethollet.
    *Proved that the relative quantities of any given pure chemical compounds constituent elements remain invariant regardless of the compunds sources.
  • John Dalton

    John Dalton
    -Daltons atomic theory was the first accepted theory.
    It was the research studies on properties of atmosphere and gases in 1803, which made him realize about the particles(atoms) and their weight.
    A few of his ideas were:
    1. All elements are composed of tiny invisible particles called atoms.
    2.Atoms of the same element are identical.
    3.Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
  • Joseph Gay-Lussac

    Joseph Gay-Lussac
    *Announced the law of combining volumes in 1808. He showed that the same teperature and pressure , two volumes of Hydrogen gas reacted with one volume of Oxygen gas to produce two volumes of water(as a gas).
    Other discoveries: Gay-Lussac and one of his peers in college participated in research in electrochemical research. They decomposed boric acid by using fused potassium, thus discovering the element boron.
  • Michael Faraday

    Michael Faraday
  • Dmitri Mendeleev

    Dmitri Mendeleev
    1869: On 6 March 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight and valence.
    -Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on atomic mass, which he published in Principles of Chemistry in 1869
  • Wilhelm Conrad Rontgen

    Wilhelm Conrad Rontgen
    First work was publoshed in 1870 dealing with specific heats of gases, followed by a few years later by a paper on the thermal conductivity of crystals.
    1895- He was studying the phenomena accompanying the passage of an electric current through a gas of extremley low pressure.*Rontgens work on cathode rays led hime to the discory of new and ifferent kinds of rays.
  • Henry Moseley

    Henry Moseley
    Discovered that the energy of X-rays emitted by the elements increased in a linear fashion with each succesive element in the periodic table.
    1913- he proposed that the relationship was a funtion of the positive charge on the nucleus. this rearranged the periodic table by using the atomic number instead of atomic mass to represent the progression of elements.
  • George Johnstone Stoney

    George Johnstone Stoney
    -published 75 scientific papers in a variety of journals but mainly in the journals of the Royal Dublin Society.
    *Made significant contributes to cosmic physics and theory of gases. He estimated the number of molecules ina cubic millimetre of gas at room temp. and pressure.
    **Most important conception and calculation of the magnitude of the "atom of electricity".
    1891: "Electron" created to describe fundamental unit of electrical charge.
  • JJ Thompson

    JJ Thompson
    Model Name: Plum pudding model.
    Showed that cathode rays were composed of a previously unknown negatively charged particle(and he is credited with the discovery of the electron),
    While exploring into the composition of canal rays , thomspon was the first to find evidence of isotopes in a stable element in 1913.
  • Marie Curie

    Marie Curie
    Marie and her husband worked together,Working with the mineral pitchblende, the pair discovered a new radioactive element in 1898. They named the element polonium, after Marie's native country of Poland. They also detected the presence of another radioactive material in the pitchblende, and called that radium.
    1910- succeded in isolating radium , she also defined an international standard for radioactive emissions.
    * Won 2 Noble Prizes
    -1921,was the first woman to recieve a nobel prize in chem.
  • Ernest Rutherford

    Ernest Rutherford
    1898:Studied radiations emitted from uranium and Thorium and named them Alpha and beta.1911: It was Rutherford's interpretation of this data that led him to formulate the Rutherford model of the atom in 1911 – that a very small charged nucleus, containing much of the atom's mass, was orbited by low-mass electrons.He is widely credited with first "splitting the atom" in 1917 in a nuclear reaction between nitrogen and alpha particles, in which he also discovered (and named) the proton.
  • Phillip Lenard

    Phillip Lenard
    In 1902 lenard showed that an electron must have a certain minimum energy before it could pass through a gas.
    In 1903 he published his conception of the atom as an assemblage of what is called "dynamides": very small and were seperated by wide spaces, they had mass and were imagined as electric dipoles.
  • Frederick Soddy

    Frederick Soddy
    Education:Uncersity of Oxford.(first class honours)
    Worked with Ernest Rutherford on radioactivity.
    1903:(W/ Sir William Ramsay) verified that the decay of radium produced Alpha particles composed of positively charged nuclei of Helium.
    1921: Recieved Nobel Prize in Chemistry& the same year he was elected member of the International Atomic Weights Committee.
    1936:He rediscovered the Descartes' theorem in 1936 and published it as a poem, "The Kiss Precise", quoted at Problem of Apollonius.
  • Henri Becquerel

    Henri Becquerel
    **French physicist
    -Nobel laureate and the discovery of radioactivity along with Marie Skoldowska -Curie and Pierre Curie: for all three won a nobel prize in physics in 1903.
    *The SI unit for radioacticity , the becquerel is named after him.
    By May 1896, after other experiments involving non-phosphorescent uranium salts, he arrived at the correct explanation, namely that the penetrating radiation came from the uranium itself, without any need for excitation by an external energy source
  • Hantaro Nagaoka

    Hantaro Nagaoka
    Nagaoka developed an early planetary model of the atom.
    * He proposed an alternative model to JJ thompsons model, which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings.
    Nagaoka's model was based around an analogy to the explanation of the stability of the Saturn rings.
    his two ideas:
    a very massive nucleus (in analogy to a very massive planet)
    electrons revolving around the nucleus, bound by electrostatic forces
  • Albert Einstein

    Albert Einstein
    *Published the famous equation:E=mc2
    In 1915 he abandoned one of his experiments he started in 1911:theory of general relativity, light from another star would be bent by the Sun's gravity. he realized the whole argument was invalid.1916: He realizedt hat the principle of relativity could also be extended to gravitational fields, and with his subsequent theory of gravitation in 1916, he published a paper on general theory of relativity.n 1921, Einstein was awarded the Nobel Prize in Physics.
  • Robert Millikan

    Robert Millikan
    Determind the unit charge of the electron in 1909 with his Oil drop experiment at the University of Chicago.
    -allowing for the calculation of the mass of the electron and the positivelyn charged atoms. e=1.60*10^-19 Coulombs.
    1923: Millikan went on to win the 1923 Nobel Prize for Physics, in part for this work, and Fletcher kept the agreement a secret until his death
  • Hans Greiger

    Hans Greiger
    *German Physicist
    1911: Greiger and John Mitchell Nuttall discovered the Greiger-Nuttall Law(relates the decay constant of a radioactive isotope with the energy of the alpha particles emitted,), and performed experiments that lead to Rutherfords atomic model.
    Inventions: Geiger Counter- instrument for measuring Ionizing radiation.
    1929:Awarded Hughes Medal.
  • Neils Bohr

    Neils Bohr
    Occupation:Danish physicist and recieved a nobel prize for his contributions for the atomic theory and quantum theory in 1922.
    Bohr proposed that an electron is found only in specific circular paths , or orbits, around the nucleus.
    *Bohr was a student of Rutherfords
    Bohr was also responsible for the electron cloud: in 1912 he came up with the theory that the electrons do not spiral in the nucleus, and came up with rules about what does happen.
  • Francis Aston

    Francis Aston
    Education: University of Cambridge · University of Birmingham · Trinity College, Cambridge · Malvern College
    1920- Invented the spectrograph. He was the first person to observre isotopes. He observed that there were three different kinds of hydrgoen atoms.
    -while most atoms had a mass number of 1, he also observed hydrogen atoms with mass nnumber 2 and 3. His work led to Rutherford predicting the existence of the neutron.
    **Nobel prize(1922) Hughes medal(1922)
  • Heisenberg

    Heisenberg
    Heisenberg was known as one of the greratest Physicists of the twentieth century. He was alsoknown as a founder of Quantum mechanincs,
    * Was one of the leaders of Germany;s Numclear Fission research
    1927: In 1927 he published his uncertainty principle, upon which he built his philosophy and for which he is best known..
    Werner Heisenberg stated that the more precisely the position of some particle is determined, the less precisely its momentum can be known, and vice versa
  • Erwin Schrodinger

    Erwin Schrodinger
    Awards:Nobel Prize in physics(1933), Max Planck medal (1937) ,Erwin Schrodinger (1956)
    * Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom.
  • Paul Dirac

    Paul Dirac
    Diracs principles of quantum mechanics published in 1930, a landmark in the history of science.
    1933: following the 1931 paper on Magnetic Monopoles, Dirac showed the existence of a single magnetic monopole in the universe would suffice to explain the observed quansitation of electrical charge.He began to work on quantum mechanics as soom as Heisneberg introduced in 1925: he independently produced a mathematical equivalent ,consisted of noncommunative algerbra, for Atomic properties.
  • James Chadwick

    James Chadwick
    1851: awarded the Exhibition Scholarship and proceeded to work under Professor H. greiger.
    In 1932 chadwick made a fundametnal discovery in the domain of the nuclear science: He proved the existence of neutrons - particles devoid of any electrical charges.
    Schrodinger was correct about his atomic theory. Electrons are constantly moving and cannot be given a definite position within the atom. They are given probable regions and are called Atomic Orbitals.
  • Glenn Seaborg

    Glenn Seaborg
    **Best known for discovering Plutonium with Edwin McMillan and all furhter transuranium elementss through 102.
    In 1951 Seaborg and Mcmillan shared the Nobel Piece prize in Chemsitry.Seaborg and his colleagues were able to create 9 other new transuranic elements (americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and element 106). In August 1997, element 106 was named in his honor, seaborgium (Sg).