Atom History

History of Atomic Theory

Timeline

~400 BC

Democritus

~400 BC

Democritus

Matter = Made up of tiny individual particle “atomos”

1803

John Dalton

1803

1. Matter is made up of atoms that are indivisible and indestructible. 2. All atoms of an element are identical. 3. Atoms of different elements have different weights and different chemical properties. 4. Atoms of different elements combine in simple whole numbers to form compounds

John Dalton

1897

J. J. Thomson

Electrons using a cathode ray tube.

J. J. Thomson

Robert Millikan 1909

Oil drop experiment - the charge of a single electron

Robert Millikan 1909

Ernest Rutherford 1911

Dense, positively charged center within the atom called the nucleus Gold Foil (alpha particle) experimentAlpha & Beta Particles

Ernest Rutherford 1911

Niels Bohr 1922

Bohr’s Orbit Model Electrons orbit the nucleus. Model based on the hydrogen atom Energy of the electrons is quantized.

Niels Bohr 1922

James Chadwick 1932

Rutherford’s data -> presence of neutral particle in the nucleus

James Chadwick 1932

Schrödinger 1933

Schrödinger 1933

Electrons can act like particles and waves (just like light) Electrons occupy orbitals.

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