Democritus asked could atoms be cut in half. He later discovered they could not be cut. He though an atom looked like a round sphere
Dalton proposed that all matter was composed of atoms, indivisible and indestructible building blocks. He used other scientist information to get his results. He led the experiment leading to the acceptance of the atom.
Millikan performed an oil drop experiment that helped to quantify the charge of an electron
Rutherford was the first to discover that atoms have a small charged nucleus surrounded by largely empty space
Bohr created the Bohr Model. It shows the atom as a small, positively charged nucleus surrounded by orbiting electrons.
He developed the matrix mechanics formula
Schrodinger used mathematical equations to describe the likelihood of finding an electron in a certain position.
Chadwick discovered the neutron in atoms.