Democritus, a greek philosopher, along with his teacher, Leucippus, thought that all matter was made of invisible elements
John Dalton, a British chemist and physicist, developed a theory that all matter is made of atoms that have different weights. He also proposed that these atoms are spherical and are in constant motion.
A primitive cathode ray tube was invented by Sir William Crookes.
The theory that radioactive particles cause atoms to break down then taking the form of energy and subatomic particles is theorised by Pierre and Marie Curie.
JJ Thomson discovers the electron, using cathode rays
Max Planck introduced the quantum theory - stating that electromagnetic energy could only be emitted in quantized form.
Einstein creates special theories of relatively and hypotheses about the particle nature of light.
Robert Millikan measures the charge of a single electron.
Ernest Rutherford developed the theory for the structure of an atom.
Neils Bohr developed the Bohr atomic model, with electrons travelling around the nucleus and the chemical properties being determined by the number of electrons.