History of an Atom Timeline

Democritus was first to suggest exsistence of atoms. He believed atoms were indestructible and indivisible.

John Dalton pictures atoms as tiny indestructible particles, with no internal structure.

Dalton's Atomic Theory.

Observed a cathode ray tube and found rays traveling in the direction opposite of the cathode ray. This was evidence for a positively charged particle called a proton.

Discovered the electron. This later leads to his "plum-pudding" model. He pictures electrons embedded in a sphere of positive electrical charge.

Suggests that an atom has a central nucleus and that electrons move in orbit.

Atoms have a small, dense, positively charged nucleus with electrons moving around it.

Believed the electron moves in a circular orbit at fixed distances from the nucleus.

Did experiments to find quantity of charge carried by an electron. He ended up calculating the mass of an electron.

Proposes that moving particles like electrons have some properties of waves. After a few years experimental evidence supported this idea.