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Newton writes about forces of attraction
Sir Isaac Newton writes about the possible existence of unseen electrical forces of attraction that hold matter together. -
Modern Definition of "Element" is Accepted
Most scientists at this time accepted the modern defiinition of an element: a substance that cannot be broken down into any simpler substances. -
Dalton's Atomic Theory
John Dalton explains the law of conservation of mass, the law of definite proportions, and the law of multiple proportions in his Atomic Theory. -
First Periodic Table of Elements
Dmitri Mendeleev aranged 7 elements into groups according to atomic mass and chemical properties. -
J.J. Thomson experiments with cathode rays
Later, Thomson's experiments are replicated, leading to the discovery of subatomic particles. -
Discovery of the Electron
Robert Millikan discovers the electron -
Discovery of the Nucleus
Ernest Rutherford, Hans Geiger, and Ernest Marsden discover the nucleus. During an experiment, Rutherford aimed alpha particles at a thin gold foil, expecting them to pass through the foil. Most of the particles did, but a small quantity "bounced back," suggesting that the particles bounced off of something in the gold foil. -
Bohr Model Proposed
Niels Bohr proposed a model often compared to the solar system. He believed that electrons orbited the nucleus like the planets orbit the sun. -
Proton is named
Ernest Rutherford names the positively charged particle of an atom the "proton" -
Idea of the neutron is proposed
Idea of the neutron is proposed by Ernest Rutherford -
Chadwick proves the existence of neutrons
James Chadwick proves that neutral particles in atoms, neutrons, exist.
