Evolution of Atomic Model

By danielalznogzz
  • 400 BCE

    Democritus

    Democritus
    -Based on the four elements -He thought atoms didn't exist -He didn't think particles could be in constant motion in a void -His theory was used for almost 2000 years, until after the scientific revolution
  • 350 BCE

    Aristotle

    Aristotle
    -Based on the four elements
    -He thought atoms didn't exist
    -He didn't think particles could be in constant motion in a void
    -His theory was used for almost 2000 years, until after the scientific revolution

  • Antoine Lavoisier

    Antoine Lavoisier
    • He noticed that it never behaved like it was a mixture of different substances, concluded that it was an element
    • He believed that this would be true for all chemical changes . This is now called the law of conservation of mass.
    • Although he did not do any work relating to atoms, his work laid the groundwork for thinking about elements.

  • John Dalton

    John Dalton
    -Recognized the existence of atoms and elements
    - Assigned a relative atomic weight of one to hydrogen, from that developed a relative atomic weight scale from assumed atomic ratios
    Proposal of the atomic theory in 1803
    All matter is made of atoms. Atoms are indivisible and indestructible.
    2) All atoms of a given element are identical in mass and properties
    3) Compounds are formed by a combination of two or more different kinds of atoms.
    4) A chemical reaction is a rearrangement of atoms

  • Joseph Gay-Lussac

    Joseph Gay-Lussac
    Law of combining volumes in 1808 – at the same temperature and pressure, two volumes of hydrogen gas react with one volume of oxygen gas to produce two volumes of water.
    • Found that if you take a specific volume of gas and raise the pressure, the temperature increases.
    • Gay-Lussac never worked with the atomic theory, but his combinations of gases were a great advance.

  • Amedeo Avogadro

    Amedeo Avogadro
    Avogadro also astutely reasoned that simple gases were not formed of solitary atoms but were instead compound molecules of two or more atoms. Avogadro did not actually use the word atom; at the time the words atom and molecule were used almost interchangeably. He talked about three kinds of “molecules,” including an “elementary molecule”-what we would call an atom.

  • Henri Becquerel

    Henri Becquerel
    -Worked with properties of the atom, such as magnetism and radioactivity
    -Found that some atoms have natural radioactivity
    -His discovery of radioactivity allowed later scientists to perfect the atomic model

  • JJ Thomson- Plum Pudding Model

    JJ Thomson- Plum Pudding Model
    Discovered electron
    -The atom was positive and there were negative forces wandering around it
    -discovered atoms of the same element but different atomic weight

  • Marie and Pierre Curie

    Marie and Pierre Curie
    -Explored the mysteries of radioactivity
    -Discovered the elements radium and polonium after investigating uranium ore Marie found that it wasn't just the uranium that was radioactive, but also other new elements.

  • Planck

    Planck
    -Quantum Theory
    -Energy is given off in little packets
    -Energy in wave form is restricted to specific quantities
    -Led to understanding of atom levels and advancement in the atomic model

  • Robert Millikan

    Robert Millikan
    -Very interested in J.J. Thomson's finding of the electron. J.J. Thomson predicted that the electron was 1000 time smaller than the atom
    -Involved in the Quantum Theory after he was inspired by Max Planck
    "Oil Drop Experiment":
    -Determined unit the unit charge of an electron
    e = 1.60 x 10-19 coulombs
    -Also determined their mass:
    m = 9.11 x 10^ -28 gram
    -Inspired other scientists to explore parts of the atom

  • Rutherford

    Rutherford
    (Thought Thomson was wrong)
    •thought of an atom having a positive nucleus with negative electrons surrounding it
    •Atom was mostly empty
    - Came to this conclusion through the "Gold Foil Experiment"
    -Had particles pass through gold foil with detective screen surrounding them
    -The particles that didn't pass made him come to the conclusion that most of the atom is empty space
    -Flaws: thought electrons contained charges that are accelerating

  • Henry Mosely

    Henry Mosely
    -Worked with Niels Bohr in order to create the real atomic number
    -Used X-rays to find the frquencies of elements on the periodic table
    -Used these frequencies to find that the number of protons in the nucleus correlated with the atomic number
    "The atomic number of an element is equal to the number of protons in the nucleus". -Moseley

  • Niels Bohr

    Niels Bohr
    -Decided to make a new model based off of Rutherford's model, but changed the orbit of the electron
    -Created energy levels in the atom, where only a certain amount of electrons could fit on one energy level of the atom
    -Used Planck's ideas in order to create quantum mechanics

  • Ernest Marsden

    Ernest Marsden
    -Contribution to Rutherford atomic model while experimenting with alpha particles
    -Used Rutherford's gold foil experiment
    -Discovered proton
    -Found connection between He atomic number and the nuclear charge

  • James Chadwick

    James Chadwick
    -Discovered the neutron in 1932
    -Discovery of the neutron led directly to the discovery of fission because he found out that sice neutrons have no electrical charge they could spilt the nucleus without anything to get in their way.
    and ultimately to the atomic bomb

  • REFERENCES

    [http://www.timetoast.com/timelines/history-of-the-atomic-model--36]
    [http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm]
    [http://profmokeur.ca/chemistry/history_of_the_atom.htm]
    [http://improbable.org/era/physics/atom.html]
    [http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/The-Atomic-Theory-687.html]
    [http://pmrb.net/blog/tag/gay-lussac/]
    [http://www.timetoast.com/timelines/the-history-of-the-atomic-theory--4]