Scientists

Aristotle

 proposed that all matter is composed of the four elements: air, fire, earth and water and not made of tiny particles “atoms”

Democritus

Proposed that matter is made up of tiny particles surrounded by empty space that cannot be split and he called them atoms

Bohr

Proposed __ model, suggesting electrons orbit a nucleus in specific, quantized energy levels or shells, rather than randomly

JJ Thomson

Discovered the electron (plum pudding; depicts the electrons as negatively-charged particles embedded in a sea of positive charge)

Dalton

proposed the first modern atomic theory; all matter is made of atoms but suggested that atoms of the same element are identical to each other, and atoms of different elements are different and have different masses. He stated that atoms can form compounds when combined and that atoms can’t be created, divided or destroyed in chemical reactions 

Millikan

found an accurate determination of the charge and mass of an electron via the oil drop experiment

Rutherford

Discovered the atomic nucleus via gold foil experiment

Moseley

revealed that the fundamental property of an element is its atomic number (number of protons), not its atomic weight

Schrödinger

Quantum Mechanical Model showed that electrons do not follow fixed paths but exist in regions called orbitals, where they are most likely to be found

Chadwick

discovered the neutron

de Broglie

 proposed that electrons behave both like particles and wave