Atomic Theory Scientists and their contributions

Antoine Lavoisier

determined the Law of Conservation of Matter by extensive experimentation

Joseph Proust

determined the law of constant composition (compounds always contain the same proportion, by mass, of elements)

Niels Bohr

developed the quantized orbit model of the atom, electrons can only reside in certain energy levels

James Chadwick

discovered the neutron

The Curies (Marie and Peirre)

discovered two other radioactive elements, polonium and radium

Erwin Schroedinger

expanded the idea that electrons behaved as particles AND waves, this developed the quantum mechanical model of the atom

Democritus

first proposed the idea that all matter was made up of tiny indivisible particles called atomos

John Dalton

formulated an atomic theory of matter with 4 postulates: 1. Elements are composted of small particles called atoms. 2. All atoms of a given element are identical. * 3. Atoms are neither created nor destroyed in chemical reactions. 4. Compounds always contain the same proportion of elements.

Henry Moseley

found that all atoms of a given element contained the same number of protons in the nucleus

J.J. Thompson

performed a CRT experiment and determined that the ray was composed of negative particles, call these electrons, determined the mass-charge ratio for an electron, came up with the "plum pudding" model of the atom

Robert Millikan

performed an "oil-drop" experiment, determined the charge of one electron and using the known mass-charge ratio, was able to calculate the mass on one electron (9.11x10^-28g)

Ernest Rutherford

performed the gold foil experiment, determined that atoms contained a very small, positively charged core at the center, called this core the nucleus, came up with the nuclear model of the atom (with electrons orbiting around the nucleus)