Dobereiner: grouped elements into triads based on like properties (gas, liquid, solid)

Newlands: grouped elements based on atomic masses into octaves (rows of 8)

Mendeleev: based his arrangement on atomic mass and columns with similar properties

Moseley: based his arrangement on atomic number

Democritus: matter is composed of tiny indivisible particles

Dalton’s Atomic Theory: each element is composed of atoms, atoms of the same element are alike and differ from any other element, atoms cannot be created nor destroyed by rxn, atoms combine in simple whole number ratios

Benjamin Franklin: an object could have one of two charges

Michael Faraday: connected electrical current with the structure of an atom

Eugene Goldstein: designed the Cathode Ray Tube and defined the charge of the proton as positive

JJ Thomson: defined the charge of the electron as negative, designed the mass spectrometer, and began to define the mass of the electron, found the mass of proton to be 1837x mass of electron

Robert Millikan: defined the mass of the electron using the “Oil Drop Experiment”

Ernest Rutherford: Gold Foil Experiment and found that the nucleus is central and positive and contains most of the atom’s mass