AP Chem Topic #2 Atoms & Beyond

Democritus

Described the world as made up of tiny indivisible particles called “atomos.”

John Dalton’s theory

Explained the Law of Constant Composition and Law of Conservation of Mass

Law of Multiple Proportions (predicted by Dalton)

When two elements combine to form two or more compounds, the ratio formed from each compound’s mass ratio always yields a fraction. (Elements cannot combine with random compositions. The number of atoms of each element in a compound must be a whole number.)

Dalton’s Atomic Model

All matter consists of tiny, indivisible particles.

J.J. Thomson

Conducted the Cathode Ray Experiment, Discovery of the electron, Plum-pudding atom

Millikan’s oil drop experiment

Determined how much charge an electron has

Becquerel

Discovered that a compound of uranium spontaneously emits high-energy radiation.

Rutherford’s Gold foil experiment

The atom is mostly empty space but has a dense center (nucleus) with positive charge too (Most alpha particles passed the gold foil, but some alpha particles deflected).

Rutherford

Revealed 3 types of radiation: alpha, beta, and gamma.

Chadwick

Discovered the neutron