Atomic Theory

Democritus (Greek Era)

Oct 9, 1001

"by convention bitter, by convention sweet, but in reality atoms and void" Something filled the void between all matter. Thus creating atoms.

Isaac Newton

Oct 9, 1704

Proposed a mechanical universe with small solid masses in motion.

John Dalton

Oct 9, 1803

Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.

Dmitri Mendeleev

Oct 9, 1869

Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law.

J.J. Thomson

Oct 9, 1897

Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram. Also, Studied "canal rays" and found they were associated with the proton H +.

Rutherford

Oct 9, 1898

Studied radiations emitted from uranium and thorium and named them alpha and beta.

Albert Einstein

Oct 9, 1905

Published the famous equation E=mc 2 Means that Energy is equal to Mass times the speed of light squared. No object with mass can ever go faster than the speed of light.

R.A. Millikan

Oct 9, 1909

Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron.

Ernest Rutherford

Oct 9, 1911

Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.

James Chadwick

Oct 9, 1932

Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.