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460 BCE
Democritus
460-370 B.C.E. born Abdera, Greece died in Greece. The theory of Democritus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms, there lies empty space; that atoms are indestructible, and have always been and always will be in motion; that there is an infinite number of atoms and of kinds of atoms, which differ in shape and size. -
John Dalton
Dalton grew up in Eaglesfield Cumberland England and died in Manchester England. Dalton’s atomic theory proposed that all matter was composed of atoms indivisible and indestructible building blocks. While all atoms of an element were identical different elements have atoms of differing size and mass. Dalton’s atomic theory stated all compounds were composed of combinations of these atoms in definite ratios. -
J.J. Thomson
Thompson lived in the U.K.; in 1897, he discovered the electron by experimenting with a cathode ray (Crookes) tube in which he constructed a glass tube with wires inserted on both ends. As they pumped out air and electric charge would pass across the tube from the wires and create and fluorescent glow. This was known as a cathode ray and later known as an electron gun; He won the Nobel Prize in physics; He developed the Plum Pudding model of the atom in 1904. He died in 1940. -
Robert Millikan
Millikan lived in the U.S.; in 1909, determined the electric charge carried by an electron in his oil drop experiment, in which he suspended small drops of oil between 2 metal electrodes by balancing downward gravitational force with upward drag and electrical forces; won the Nobel Prize for physics in 1923. He died in 1953. -
Ernest Rutherford
Rutherford grew up in New Zealand then lived in England; in 1911 he discovered the nucleus of the atom, protons within the nucleus, and electrons that circle the atom (called Rutherford’s atom); he discovered this in his gold foil experiment, where he shot a beam of alpha particles at a sheet of gold foil and some particles were deflected; known as the father of nuclear physics and he won the Nobel Prize for chemistry in 1908. He died in 1937. -
Neils Bohr
He was born in Copenhagen Denmark. In 1913 Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus. He modified the model by requiring that the electrons move in orbits of fixed size and energy. He stated that the energy of an electron depends on the size of the orbit and is lower for smaller orbits. The atom will be completely stable in the state with the smallest orbit. He died in 1962. -
Erwin Schrodinger
He was born in Vienna, Austria. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom.This model has a nucleus surrounded by an electron cloud (Electron Cloud Model). He died in 1961. -
James Chadwick
He was born in Cambridge United Kingdom. The discovery earned Chadwick the 1935 Nobel Prize in physics for the discovery of the neutron and it made possible the development of the atomic bomb. Chadwick participated in the Manhattan project which deployment of nuclear bombs in Japan. He studied the transmutation of elements by bombarding them with alpha particles and investigated the nature of the atomic nucleus identifying the proton the nucleus of the hydrogen atom He died in 1974.
