Atomic Structure Timline

The development of the atomic theory

Period: 400 to Nov 7, 2011

Democritus

460

http://www.youtube.com/watch?v=TgWn91ap99ADemocritus said that matter was composed of small particles called "atoms" that could be divided no further. His basic ideas were found in philosophical reasoning, not experimental testing. He called them atoms because in Greek "atomos" means indivisible.

Lavoisier

Sep 30, 1782

http://www.youtube.com/watch?v=dExpJAECSL8Made measurements of a chemical change in a sealed container. Lavoisier came up with the Law of Conversation of Mass. This law states that when a chemical reaction occurs, mass is neither created nor destroyed but only changes.

Proust

Nov 8, 1799

http://www.youtube.com/watch?v=eQOTy6JUjEgA french chemist who observed that the composition of water is always 11% hydrogen and 89% oxygen by mass. Came up with the Law of Definite Proportions which states that compoounds have a consistent ration of elements.

Dalton

Aug 15, 1803

http://www.youtube.com/watch?v=07yDiELe83YThe father of the Atomic theory

J. J. Thomson

Nov 9, 1896

http://www.youtube.com/watch?v=XU8nMKkzbT8Experimented with a cathode ray tube and concluded that electrons are invisible negatively charged particles, and protons are invisible positively charged particles.

Rutherford

Nov 9, 1910

http://www.youtube.com/watch?v=Q8RuO2ekNGwHe proformed the Gold Foil Experiment and came up with the plum pudding model of an atom. He said that the mass of an atom is positive and the dots are the negatively charged electrons.

Millikan

Nov 9, 1910

http://www.youtube.com/watch?v=XMfYHag7LiwProformed the Oil Drop Experiment and concluded the mass of one electron is 1/1840 the mass of a proton. Essentially the electron has no mass.

Chadwick

Nov 9, 1932

http://www.youtube.com/watch?v=_nky2XQGQ3kProved the exsistence of the neutron