Chemistry scientists

John Dalton (1776 - 1844)

Atomic theory: “Billiard Ball Model” (Nothing is inside an atom). He made 5 claims (2 were incorrect- He said atoms are indivisible (nothing inside) and all atoms of a given element are identical to one another). Correct claims: Every element is made up of tiny particles called atoms, atoms of 2 or more different elements combine to form compounds in the same ratios each time, atoms are never created nor destroyed in a chemical reaction- these chemical reactions involve the rearrangement, separation, or combination of atoms.

J.J. Thomson (1897)

“Plum pudding model”

He discovered the electron using a cathode ray tube. But, the actual model shows electrons embedded within a positively charged atom

Democritus (400 BC)

First to mention concept of atom

Robert Millikan (1913)

Calculated the charge of electrons (in Columbus) and the mass of electrons

Ernest Rutherford (1911-1913)

Discovered the nucleus in his “Gold Foil Experiment”. His conclusions: atom is mostly empty space, atom has a very small, dense nucleus, the nucleus has a positive charge.

James Chadwick (1932)

Discovered the neutron – located in nucleus, helps hold nucleus together. Won Nobel peace prize for discovery of neutron.

Niels Bohr (1913)

“ Planetary Model” - electrons orbit around the nucleus like planets orbit around the sun