Atomic Theory

Events

Democritus

440 B.C

Atoms are “uncuttable.”

Democritus

440 B.C

Atoms are small, hard particles.

Democritus

440 B.C

He conducted experiments in combining elements.

Democritus

440 B.C

Atoms are made of a single material formed into different shapes and sizes.

Dalton

1803

Atoms of the same element are exactly alike.

Dalton

1803

He wanted to know why elements combine in specific proportion.

Dalton

1803

All substances are made of atoms.

Dalton

1803

Atoms of different elements are different.

Rutherford

1879

His model had electrons surrounding the nucleus at a distance.

Thomson

1897

His theory of atomic structure led to the “plum-pudding” model.

Thomson

1897

He conducted the cathode-ray tube experiment.

Thomson

1897

There are small, negatively charged particles inside an atom.

Rutherford

1911

Most of an atom’s mass is in the nucleus.

Rutherford

1911

He conducted the gold foil experiment.

Rutherford

1911

Atoms contain mostly empty space

Rutherford

1911

There is a small, dense, positively charged nucleus.

Bohr

1913

Electrons travel in certain paths or energy levels.

Bohr

1913

Electrons can jump from a path in one level to a path in another level.

Rutherford

1919

He discovered another particle in the nucleus of atoms.

James Chadwick

1932

He discovered the neutral neutron.

Schrodinger and Heisenberg

2000

Electrons are found in electron clouds, not path.

Schrodinger and Heisenberg

2000

Electron paths cannot be predicted.