Democritus proposed that all matter is composed of indivisible elements.
John Dalton published his frist book, “Meteorological Observations and Essays”. This book explained the foundation of his later dicoveries.
John Dalton developed a theory that matter is simply composed of atoms of different weights. He aslo said that that these atoms are spherical and in motion.
JJ Thompson discovered the electron, using properties of cathode rays.
Ernest Ruthford, father of nuclear physics, developed the theory for the structure of the atom. He used a gold foil experiment and demonstrated for the first time the existence of the atomic nucleus.
Neils Bohr developed the Bohr atomic model. It showed that electrons travelling in orbits around the nucleus, and chemical properties being determined by how many electrons are in the outer orbits.
Erwin Shrodinger described how electrons move in wave form, and developed the Schrodinger equation which describes how the quantum state of a system changes with time.
James Chadwick discovered the neutron component of the atomic nucleus. This also made it possible to produce elements heavier than uranium in the lab.