The Introduction of the Atom

  • Period: to

    Findings in atomic structure.

  • John Dalton

    Dalton was conducting experiments on mixtures of gases which led to new hypotheses. He then tested these hypotheses to find his conclusions. He found five ideas which led to his atomic theory: 1. all matter is made of atoms, 2. atoms of the same element are identical, 3. atoms can't be created, destroyed, or divided, 4. different atoms combine in ratios to form compounds, 5. in a chemical reaction, atoms are separated, combined, or rearranged. He has contributed the modern atomic theory.
  • George Johnstone Stoney

    Stoney discovered the fundamental unit of electricity in 1874. However, it was not until 1891 that he proposed the term 'electron' to describe the fundamental unit of electrical charge. His contributions led to the discovery of the particle by J.J. Thomson in 1897.
  • J.J. Thomson

    J.J. Thomson used the cathode ray to determine the charge - to - mass ratio of a charged particle. He concluded that atoms were divisible into smaller subatomic particles, which had previously been thought to be incorrect, and that the mass of a charge particle was much less than that of a hydrogen atom, the lightest known atom. He, then, was able to discover the electron.
  • Robert Millikan

    Robert Millikan conducted an oil-drop experiment in which he detected and measured the effect of an individual subatomic particle. According to Millikan, electrons carry a charge of 1-, a negative charge. He determined the charge of the electron and also developed the plum pudding model to demonstrate his findings.
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  • Ernest Rutherford

    He conducted an experiment in which he shot alpha particles at the center of a piece of gold foil. He saw that some deflected and some passed through. From this he concluded that the center of the atom is positive (+) and that the atom contains empty space around the center. His experiments led to the discovery of the nucleus.
  • Niels Bohr

    Niels Bohr was able to depict the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus. He contributed the findings of energy levels as well as the Bohr model.
  • James Chadwick

    He did not agree with rutherford in that there was only one particle in the nucleus. He studied atomic disintegration and found that the atomic number was less than the atomic mass. He concluded that there was a neutral particle and that together, electrons, protons, and neutrons account for all of the mass of an atom. From this, he discovered the neutron.
  • Murray Gell-Man and George Zweig

    These two scientists were able to determine that there was an elementary particle and a fundamental constituent of matter called the quark. They also came up with the quark model to show their findings.
  • Martin Lewis Perl

    He found a new elementary particle known as the tau lepton. It is a superheavy cousin of the electron, the carrier of electrical current in household appliances. He discovered the lepton.