-
100
Democritus
Democritus, an ancient Greek scientist, lived from 460 BC to 370 BC., He was the first scientist to use the term "atom" to describe tiny parts of matter. -
Dalton's Atomic Theory
John Dalton was the first modern scientist to create an atomic theory. This theory did not include subatomic particles, as the later theories did. More on Dalton's Theory -
Goldstein discovers canal rays
In 1886, Eugen Goldstein discovered that along with cathode rays, there was another, lesser ray that could be seen when applying electricity to the system. This ray traveled in the opposite direction of the cathode rays. After Thomson made the discovery of the electron in 1897 using this same apparatus, it was deduced that what Goldstein had actually found was protons. -
J. J. Thomson
In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. -
R. Millikan
Determines the mass of the electron using the oil drop experiment. -
Rutherford discovers nucleus
Rutherford performed an experiment using alpha radiation and thin gold foil. He thought that the radiation would pass straight through the foil, confirming Thomson's idea that negative particles were evenly distributed throughout a positive mass. What he actually found was that rays were deflected in odd directions, indicating that the mass of the atom was centralized. He had discovered the nucleus. Learn More -
Niels Bohr
Niels Bohr created the planetary model of the atom, which stated that electrons traveled around the nucleus in set orbitals, similar to the planets around the sun. -
James Chadwick
James Chadwick discovered the neutron, and found that it weighed approximately the same as a proton.
