Key Discoveries and Models in Atomic Theory: Dalton to Chadwick

John Dalton

Experiment: Studied the weights of various gases and how they reacted.

Contribution: Formulated the first scientific atomic theory.

Contribution: Stated that elements consist of identical, indestructible atoms.

Contribution: Stated that atoms combine in fixed, whole-number ratios.

JJ Thomson

Experiment: Cathode Ray Tube experiment (bent electrical rays using magnets).

Contribution: Discovered the electron.

Contribution: Proved that atoms are divisible into smaller subatomic particles.

Contribution: Proposed the "Plum Pudding" model of the atom.

Robert Millikan

Experiment: Oil Drop experiment (balanced charged oil droplets between electrical plates).

Contribution: Measured the exact negative charge of an electron.

Contribution: Calculated the incredibly tiny mass of an electron.

Ernest Rutherford

Experiment: Gold Foil experiment (fired alpha particles at thin gold sheets).

Contribution: Discovered the nucleus.

Contribution: Proved the atom is mostly empty space.

Contribution: Discovered that the nucleus is tiny, dense, and positively charged.

Niels Bohr

Experiment: Analyzed the light emission spectra of hydrogen gas.

Contribution: Created the planetary model of the atom.

Contribution: Stated that electrons move in fixed, quantized energy orbits.

Contribution: Showed that electrons emit light when jumping between energy levels

James Chadwick

Contribution: Discovered the neutron.

Contribution: Proved the neutron has no charge but has a mass similar to a proton.

Contribution: Completed the basic model of the atomic nucleus.