History of Atoms

Democritus

200

Over 2,500 years ago Democritus suspected that matter had extremely little particles that couldn't be divided. He believed that there were different types of atoms for different types of matter.

Aristotle

300

Aristotle believed that there wasn't a specific amount of times matter can be divided, He believed that everything was made only of air, fire, earth and water.

John Dalton

Sep 6, 1766

John Dalton noticed that all compounds no matter the size the ratio of elements in a compound are always the same. He iscovered thsat this was because of atoms. The main points Dalton addressed were: all elements are made of atoms ; all atoms of the same element have the same mass; compounds contain atoms of more than one element; and in a perticular compound, atoms of different elements combine in the same way.

J.J. Thomson

Dec 18, 1856

Thomson added more than one thing to he knowledge about atoms. He learned that atoms were made of smaller particles than was originally thought. Thomson also learned that particles in an atom are neutral. He discovered this by placing metal disks on opposite sides of a glasstube and watched to see what happened to the beam when the plates were moved.

Hantaro Nagaoka

Aug 15, 1865

Nagaoka thinks an atom has a nucleus. And that positive and negative charges orbit the nucleus, but cannot prove it.

Ernest Rutherford

Aug 30, 1871

Proved that every atom has a positive charge in the center which he named a nucleus. This was proved when he learned that not all alpha particles were deflected off gold.

Niels Bohr

Oct 7, 1885

Proved that electrons moved in a spherical orbit around a nucleus. He also proved that electrons gain or lose energy when they move between energy levels.

Erwin Schrodinger

Aug 12, 1887

Came up with math equations to describe how electrons move in atoms. The work he presented concluded to the Electron Cloud Model.

Ernest Marsden

Feb 19, 1889

He was a student of Rutherford. He is known for his part in helping Rutherford's atomic theroy. HE was the one who noticed that when alpha particles were fired at a gold foil they were deflected back.

James Chadwick

Oct 20, 1891

Gave proof that neutrons are real. Neutrons have no charge. Nucleui contain neutrons and positively charged protons.

Louis de Brogile

Aug 15, 1892

Suggested that some particles like electrons have some properties of waves.