The Atomic Model

Events

Democritus

400 BC

He thought that all matter is made up of indestructible units called atoms. He also proposed that atoms constantly move.

Aristotle

300 BC - 1800

He thought that all matter was made of the four elements; fire, water, earth and air. He believed atoms had four different properties hot, cold, wet and dry.

John Dalton

1803

All substances are made of atoms, which he thought to be to small to see but indestructible. Atoms of different elements are different; Atoms are small, hard particles; He conducted experiments in combining elements; Atoms of the same element are exactly alike.He proposed that a chemical reaction was the rearrangement off atoms.

J.J. Thomson

1897

He discovered the negatively charged particles inside of an atom called an electron. This later leads to his "plum-pudding" model. He pictures electrons embedded in a sphere of positive electrical charge.

Ernest Rutherford

1908

Proposed that there is a small, dense, positively charged nucleus; Most of an atom's mass is in the nucleus; Atoms contain mostly empty space; Electrons move in empty space in the atom; He conducted the gold foil experiment.

Neils Bohr

1913

He believed the electron moves in a circular orbit at fixed distances from the nucleus. The mass of an atom was mostly in the nucleus.

Erwin Schrodinger

2000

Erwin Schrodinger created the Electron Cloud Model which demonstrated the idea of the electrons moving around freely in a certain area around the nucleus of an atom, changing the idea that electrons moved around the nucleus in a fixed orbit. The model proposed that scientists could only make educated guesses on the whereabouts of an atom and their locations were described as being part of a "cloud".