-
John Dalton pictures atoms and tiny, indestructible particles, with no internal structure.
-
J.J. Thomson, a British scientist, discovers the electron. The later leads to his "plum-pudding" model. He pictures electrons embedded in a sphere of positive electrical charge.
-
Hantaro Nagoka, a Japanese physicist, suggest that an atom has a central nucleus. Electrons move in orbits like the rings around Saturn.
-
New Zealand physicist Ernest Rutherford finds that an atom has a small, dense, positively charged nucleus. Electrons move around the nucleus.
-
In Niels Bohr's model, the electron moves in a circular orbit at fixed distances from the nucleus.
-
French physicist Louis de Broglie proposes that moving particles like electrons have some properties of waves. Within a few years, experimental evidence supports the idea.
-
Erwin Schroedinger develops mathematical equations to describe the motion of electrons in atoms. His work leads to the electron cloud model.
-
James Chadwick, an English physicist, confirms the existence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.