-
Dalton discovered oxygen combined with either one or two volumes of nitric oxide in closed vessels over water. -
Thomson created a model of an atom as a sphere of positive matter, and its electrons are positioned by electrostatic forces. He estimated the amount of electrons in an atom with scattering light, X, beta, and gamma rays. -
A beam of alpha particles was aimed at a piece of gold foil. Most of the particles passed through the foil, but a few were scattered. Some bounced back. This showed that most of atoms are empty space, and the nucleus has a positive charge that makes other positive particles bounce off. -
Bohr proposed a theory on hydrogen atoms that some physical quantities only take discrete values. -
Chadwick proved the existence of isotopes through discovery of neutrons. Isotopes have the same number of protons and neutrons.