Atomic Timeline

Main

Atoms constantly move. 440 B.C. (Democritus)

440 B.C.

Atoms are small, hard particles. 440 B.C. (Democritus)

440 bc

Atoms are “uncuttable.” 440 B.C. (Democritus)

440 bc

Atoms of different elements are different. 1803 (Dalton)

1803

Atoms of the same element are exactly alike. 1803 (Dalton)

1803

All substances are made of atoms. 1803 (Dalton)

1803

He conducted experiments in combining elements. 1803 (Dalton)

1803

Elements combine in specific proportions. 1803 (Dalton)

1803

His theory of atomic structure led to the “plum-pudding” model. 1897 (Thomson)

1897

He conducted the cathode-ray tube experiment. 1897 (Thomson)

1897

Thomson, There are small, negatively charged particles inside an atom.1897

1897

There are small, negatively charged particles inside an atom.

There is a small, dense, positively charged nucleus. 1911 (Rutherford)

1911

Electrons move in empty space in the atom. 1911 (Rutherford)

1911

Atoms contain mostly empty space. 1911 (Rutherford)

1911

Most of an atom’s mass is in the nucleus. 1911 (Rutherford)

1911

He conducted the gold foil experiment. 1911 (Rutherford)

1911

Electrons jump between levels from path to path. 1913 (Bohr)

1913

Electrons travel in definite paths. 1913 (Bohr)

1913

Electron paths cannot be predicted. (Schrödinger and Heisenberg)

2000

Electrons are found in electron clouds, not paths. Schrödinger and Heisenberg

2000