Atomic Theory Timeline

Democritus

400 BCE

Democritus created the earliest documentation of the idea of an atom. He called the smallest piece of matter "atomos," meaning, "not to be cut." He believed atomos were small, hard, indivisible particles that were made up of the same material but manifested itself into different shapes and sizes.

Aristotle (Dishonorable Mention)

300 BCE

Aristotle was a complete doofus who is credited with causing the death of chemistry for 2,000 years. At the time, his views were widely accepted - that all matter was made up only of fire, earth, air, and water, and that atoms played no role. He also stated that matter had four properties; hot, cold, dry, and wet. Can you believe this guy? Seriously. Total goober.

John Dalton

1803

John Dalton revived the theorization of the atom after Aristotle killed the idea for 2000 years. Dalton performed numerous experiments, resulting in the 1st atomic theory. He stated that all matter is made up of atoms, which are too small to see, indestructible, and uncuttable - similar to Democritus's ideas about the atom. Dalton also theorized that all atoms of an element are exactly alike and atoms of different elements are different.

J.J. Thomson

1897

Thomson introduced a hint of the idea that atoms could be made of even smaller particles with his discovery of the electron, a negatively charged particle. His findings led to the discovery of the proton, a positively charged particle, and the neutron, a neutral particle, by future scientists. Thomson also created the plum pudding model to represent his theory of what an atom looked like. This model consisted of electrons surrounded by a volume of positive charge.

Ernest Rutherford

1908

Rutherford, like Thomson, discovered an important piece of the atom - a small, dense, positively charged center called the nucleus. This was found using his gold foil experiment. Along with this, he theorized that electrons are scattered outside of the nucleus at a distance, disproving Thomson's plum pudding model.

Niels Bohr

1913

Bohr had a similar idea to Rutherford, but wanted to improve upon his atomic model. Instead of electrons being scattered outside of the nucleus, Bohr theorized that they moved in definite orbits around the nucleus, similar to the solar system. He also believed that electrons move around energy levels located at certain distances around the nucleus.

Erwin Schrödinger

1926

Schrödinger, inspired by Bohr's model, used a multitude of equations to find the likelihood that an electron is located in a certain position. This is represented by a nucleus surrounded by an electron cloud, a model called the quantum mechanical model. It also brought about the idea of sub-energy levels.