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Democritus (B.C)
Democritus proposes the idea that all matter is made up of tiny indivisible particles called atomos, and that these are indestructible and invisible particles. -
Dalton
John Dalton proposes that elements are made up of all of one kind of atoms, and that atoms are not created nor destroyed during chemical reactions, but simply changed. He also formulated that compounds always have the same amount of each element, and that atoms are indivisible. -
Thomson
J.J Thomson shows that cathode rays are composed of negative particles, and discovers the electron. -
Thomson
J.J Thomson proposes his plum pudding model of the atom, in which electrons were the plums and positively charged matter was the pudding (which was later proved false--protons are only found in the nucleus). He also helped discover isotopes. -
Rutherford
Ernest Rutherford performs the gold foil experiment, which determined that every atom has a positive center and fast moving, negative particles around it. He came up with the nuclear model of the atom. -
Bohr
Niels Bohr comes up with his model of the atom, which depicted the atom as a mass with a positively charged center (nucleus), which was surrounded by electrons in fixed orbitals. He didn’t know about neutrons or electron clouds. -
Moseley
Henry Moseley found that all atoms of the same element have the same number of protons in the nucleus. -
Schrodinger
Erwin Schrodinger expands the idea that electrons act as particles AND waves, and develops the quantum mechanical model of the atom. His and Werner Heisenberg’s model is still used today. -
Heisenberg
Heisenberg proposs the modern model of the atom, with the electron cloud. This model, states that electrons do not follow perfect circular orbitals, but instead are found orbiting the nucleus in random areas called electron clouds. This model is still used today. -
Chadwick
James Chadwick discovers the neutron, inspiring the U.S to begin researching atomic bombs.
