Past of Atomic Theories

Aristotle (322 BCE)

322

He believed that nothig on Earth was made of atoms, but instead made of either Earth, Fire, Water, and Air. Plato helped him come to this conclusion and was soon proved wrong.

Democritus (450 BCE)

450

He stated that atoms are eternal and so small that they cannot be divided. He thought an object had to stop breaking at one point. To descover this, he took a seashell and crushed it until it couldnt be crushed anymore. After this experiment he came to this conclusion that an atom existed.

Dalton

Jun 25, 1803

Atoms that are of different elements and are joined cause chemical reactions. He believed atoms are indivisable and indestructable.

Thomson

Dec 17, 1897

Atoms were made up of even smaller particles known as electrons. He added negative electrons that float in a "soup" of positive charge.

Rutherford

Sep 29, 1911

His new model included a nucleus. He described the atom as tiny, dense, and positively charged.

Bohr

Dec 1, 1913

Proposed that the electrons could only orbit the nucleus in certain orbits at different energy levels around the nucleus. "Theory ofthe Nucleus" which states that, " any charged particle moving on a curved path emits electromagnetic radiation; thus, the electrons would lose energy and spiral into the nucleus."

Heisenburg

Oct 10, 1925

He thought that the electrn exisited as a particle. He did not experiment because the only experiment he wanted to try involved shining a light on the electrons, although this would not work because the electrons would move somewhere else.

Schrodinger

Jun 16, 1926

Claimed that Eletrons were actually made up of waves. He said, "Electrons were not just a partile that exsisted at only one point at a time, but a smeared out wave that spread through all of spce and time."