Atomic Structure

Democritus

400

Democritus’ atomic theory stated that all matter is made up small indestructible units he called atoms.

John Dalton

Oct 6, 1803

John Dalton proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together.

Plucker

Jan 30, 1859

J. Plucker built one of the first cathode-ray tubes.

Mendeleev

Apr 25, 1869

Dmitri Mendeleev created the periodic table.

Thomson

Aug 11, 1897

J.J. Thomson determined the charge to mass ratio of electrons.

Rutherford

Dec 17, 1898

Rutherford discovered alpha, beta, and gamma rays in radiation.

Planck

Feb 1, 1900

Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light.

Moseley

May 2, 1914

H.G.J. Moseley discovered that the number of protons in an element determines its atomic number.

Bohr

Mar 27, 1922

Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.

de Broglie

Sep 19, 1923

Louis de Broglie proposed that electrons act like waves/particles.

Chadwick

Jul 30, 1932

James Chadwick discovered neutrons.