Democritus proposed that all matter was made up of a small unit named atoms
John Dalton agreed that all matter was created by atoms which he believed were indestructible. He also said that compounds are created by combining two atoms.All atoms of given elements are identical in their mass and properties.
Created the periodic table which classifies elements by their similarities
Discovered positive particles. He noted that the particles had a charge equal and opposite to the electron.
J.J discovered the electron and did further experiments on it.
Ernest concluded that all positive charges were centralized while negative electrons orbited the nucleus.
The Big Year
Neils Bohr explained that outer orbits in an atom could hold more electrons than the inner orbits. By knowing this, one can determine the atom's chemical properties. Frederick Soddy came up with the concept of isotopes.
Werner Heisenberg thought of the Uncertainty Principle which states that one can never know the exact location and energy of an electron simultaneously.
Chadwick discovered the neutron which helps balance out protons in the nucleus of the atom.