History of the AtomDates are included for a frame of reference.

Democritus

Around 400 B.C. Atomos => indivisible He suggested that all substance in the

universe was made up of particles so tiny that nothing smaller was possible.

He regarded those particles as unchangeable and indestructible, and as the only content of the universe.

The “Mocker”

Dalton

1803 Atoms = small, dense, spheres Billiard Ball Model Atomic Theory

Dalton

Dalton’s Atomic Theory

Tiny particles called atoms make up all elements

Atoms of the same element are identical

Compounds are made with whole number ratios of atoms

Chemical reactions are when compounds are broken and reformed

Thomson

1897 Discovered the electron, and they

were negative Cathode Ray Tube experiment Plum pudding model

Immobile electrons

Thomson

Rutherford

1911 Gold Foil Experiment Discovered atom was mostly empty

space Discovered the nucleus

Dense, positive, small, in center Atomic Model

Rutherford

Bohr

1913 Electrons were located in shells

(fixed orbits) Electrons can move to other shells Planetary Model

Bohr

Millikan

1916 Oil-drop experiment

Mass of an electron Exact charge of an electron

Millikan’s Oil Drop Experiment

Schrödinger

1926 Electron cloud of probability Electron Cloud Model

Electron Cloud Model

Chadwick

1932 Discovered the neutron