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Democritus
Democritus's Atomic Theory Democritus lived from 460 B.C. to 370 B.C. He found that atoms are the smallest part of matter and cannot be divided. -
John Dalton
Dalton's Atomic Theory Dalton lived from 1766 to 1844. He said that all atoms are indentical in mass and properties, compounds are formed by a combination of two or more kinds of atoms, a chemical reaction is the rearranging of atoms, and that atoms cannot be created or destroyed. -
J.J. Thomson
J.J. Thomson J.J. Thomson was born December 18, 1856 and died August 30, 1940. He found that the atom had both positive and negative parts; he called the negative parts electrons. He came up with the Plum Pudding Model. -
Max Planck
Max Planck Planck was born April 23, 1858 and died October 4, 1947. He said that energy emitted by a resonator could only take on discrete values. -
Ernest Rutherford
Ernest Rutherford Rutherford was born August 30, 1871 and died October 19, 1937. He proved Thomson's model wrong and came up with the planetary model. He also descovered that the positive charge was located in the nucleus and that most of the atom was just empty space. -
Francis Aston
Francis Aston Aston was born in September of 1877 and died November 20, 1945. He discovered that all isotopes (other than oxygen's) have masses that are near whole numbers. -
James Chadwick
James Chadwick Chadwick was born October 20, 1891 and died July 24, 1974. He proved the existence of neutrons. -
Niels Bohr
Niels Bohr Bohr was born October 7, 1885 and died November 18, 1962. He presented a picture of the structure of the atom. He also found that electrons orbit the nucleus without losing energy, could only move in fixed orbits, and that ones with low energy would orbit closer to the nucleus than those with higher energy.
