The Atomic Theory

Democritus

400

400 BC -- Democritus determined that matter was made of particles called atomos, which are solid and indivisible. He also believed that atoms come in all shapes and sizes.

John Dalton

Dec 31, 1803

John Dalton developed the atomic theory. He believe that all matter was made of atoms which were identical to other atoms of the same element, but differed to other atoms of different elements. He also stated that atoms are neither created nor destroyed, but only rearranged in a chemical reaction.

J.J. Thomson

Dec 31, 1904

J.J. Thomson discovered electrons using a cathrode ray. This lead him to develope his 'plum pudding' atomic model. This model demonstrated that negatively charged electrons were distributed evenly through a positive charge.

Ernest Lord Rutherford

Dec 31, 1910

Ernst Lord Rutherford discovered the nucleus of the atom. He also believed that electrons have fixed orbitals surrounding the nucleus.

Niels Bohr

Dec 31, 1913

Niels Bohr believed in the planetary atomic model. This is where the nucleus is surrounded by electrons in orbitals with different energy levels.

Erwin Schrodinger

Dec 31, 1926

Erwin Schrodinger, a mathematician, developed the quantum mechanical atomic model. This model stated that electron orbits are in different shapes, and that they are both particles and waves of energy at the same time.