Some Developments of the Atom

Four Fundamental Substances 400 B.C.

400

Greeks proposed that all matter was composed of four fundamental substances: fire, water, earth, and air. Based on intuition Not based on experimental evidence

Dalton's Theory

Jun 7, 1808

Each element is made up of tiny particles called atoms.
The atoms of a given element are identical.
Chemical compounds are formed when atoms combine with each other.
Chemical reactions involve reorganization of the atoms. The atoms themselves are not changed in a chemical reaction.

J. J. Thomson

Jun 7, 1898

Discovered the electron.
All atoms have electrons.
Developed the plum pudding model

Ernest Rutherford

Jun 7, 1911

Metal foil experiment
Atom has a center of concentrated positive charge
Center contains most of the mass of the atom
Center called the nucleus
Nuclear Atom
Electrons move around the nucleus at a distance relative to the nuclear radius

Niels Bohr

Jun 7, 1913

Developed the quantum model for the hydrogen atom Electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits