Development of the Atomic Theory

Plato

427 BCE

Plato was the start of the atomic theory and theorized that matter, when solid, was composed of invisible triangle-shaped elements.

Democritus

400 BCE

Democritus believed that atoms were uniform, solid, hard, incompressible, indestructible, and that they moved in infinite numbers until they were stopped.

The Alchemists

500

The Alchemists believed that all metals were formed of Mercury and Sulfur and that by combining those two metals you could create any metal.

Solar System Model

1543

In 1543 Nicolaus Copernicus created the solar system model, which tells of the relative position and motion of all the planets in the solar system.

Robert Boyle

1660

Robert Boyle believed that everything was made of the very tiny particles called atoms.

Antone Lavoisier

1789

Antone Lavoisier believed that during a chemical reaction atoms were neither created nor destroyed.

Billiard Ball Model

1800

In the early 1800's John Dalton created his billiard ball model. This model stated the atom was a ball-like structure.

John Dalton

1803

John Dalton believed that all elements were formed of invisible and indivisible particles called atoms. He also believed that all matter is made of these atoms.

Amedeo Avogadro

1811

Amedeo Avogadro believed that gasses with equal volumes must also have an equal number of molecules and that elementary gasses (such as Hydrogen, Nitrogen, and Oxygen) are composed of two atoms.

Dmitri Mendeleev

1869

Dmitri Mendeleev is credited with creating the periodic table as we know it.

JJ Thompson

1897

JJ Thompson is credited with discovering the electron and he also proposed the structure of the atom.

Pierre and Marie Curie

1898

The Curies believed that radiation happened in the atoms, not on a molecular level.

Plum pudding Model

1904

In 1904 JJ Thomson created his plum pudding model. This model stated that electrons were negatively charged particles suspended in a positively charged soup.

Albert Einstein

1905

Albert Einstein was able to use math to prove that atoms existed and showed that liquids are made of molecules.

Robert Millikan

1910

Robert Millikan is credited with discovering the charge an electron carried.

Ernest Rutherford

1911

Ernest Rutherford believed that atoms had a tiny, dense positively charged core, called the nucleus, where the mass of an atom is concentrated and that the electrons orbited around.

Neils Bohr

1913

Neils Bohr believed that electrons orbited the nucleus, but only in set orbits, and if an electron were to jump or change orbits it would cause an output of radiation.

Henry G. J. Mosley

1914

Henry G. J. Mosely discovered that an atom's atomic number is equal to the number of positive charges in the nucleus.

Werner Heisenburg

1925

Werner Heisenburg is credited with helping to create the mathematical models that predict the location of electrons.

Erwin Schrödinger

1926

Erwin Schrödinger is credited with using mathematical formulas to determine the probability of finding an electron in a certain place.

Electron Cloud Model

1926

Erwin Schrödinger and Werner Heisenburg created the electron cloud model in 1926. This model stated that scientists could only calculate the likelihood of electrons being in a certain place, not actually find them.

James Chadwich

1932

James Chadwich is credited with the discovery of the neutron.