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460 BCE
Democritus
c. 460 BCE - c. 370 BCE
Democritus was the first to suggest the idea of atoms and came up with the idea that atoms were specific to the material they composed. He believed that they differed in shape and size, were constantly moving, and would collide with each other and stick together. He thought they we indivisible and indestructible. -
John Dalton
September 6th, 1766 - July 27, 1844
Dalton had the first complete attempt to describe all matter in terms of atoms and their properties and first to come up with atomic theory. He also made the concept that all matter/all elements are made of atoms, which are indivisible. Atoms of the same element are identical. Atoms can combine in simple whole-number ratios to form chemical compounds. In chemical reactions, atoms combine, separate, or rearrange, but never change. -
Eugene Goldstein
September 5th, 1850 - December 25th, 1930
Goldstein discovered positive particles (protrons) using a tube filled with hydrogen gas. The positive particle was named the proton. -
J.J Thomson
December 18th, 1856 - August 30th, 1940
Thomson experimented with cathode ray tubes which showed that all atoms contain negatively charged subatomic particles or electrons. Known for electrons. Also, he is known for the plum pudding model. -
Max Planck
April 23rd, 1858 - October 4th, 1947
Planck discovered the quantum of action, this work was the base for the quantum theory. which he won a Nobel prize for discovering the quantum of action. -
Robert Millikan
March 22nd, 1868 - December 19th, 1953
Millikan accurately determined the charge carried by an electron, using the elegant "falling-drop method". He also proved that this quantity was the same for all electrons, demonstrating the atomic structure of electricity. -
Ernest Rutherford
August 30th, 1871 - October 19th, 1937
Ernest Rutherford found that the atom is mostly empty space, with nearly all of its mass concentrated in a tiny central nucleus. The nucleus is positively charged and surrounded at a great distance by the negatively charged electrons. Used a gold foil experiment to discover the nucleus and make assumptions: the nucleus is small, dense, and positively charged. -
Dmitri Mendeleev
February 8th, 1884 - February 2nd, 1907
Mendeleev devised the periodic classification of the chemical elements, in which they were in the order of increasing atomic weight. He left blank spaces on the periodic table because he thought more would be discovered. -
Niels Bohr
October 7th, 1885 - November 18th, 1962
Bohr proposed that energy levels of electrons are discrete and that the electrons are in stable orbits around the atomic nucleus but can jump/orbit from one energy level to another. -
Erwin Schrodinger
August 12th, 1887 - January 4th, 1961
Schrodinger found a way to calculate the energy levels of electrons in atoms using a wave equation. -
James Chadwick
October 20th, 1891 - July 24th, 1974
Chadwick proved the existence of neutrons (elementary particles devoid of any electrical charge). Discovered the neutron, it is found in the nucleus. The neutron has the same mass as a proton. The neutron has no charge. -
Werner Heisenberg
December 5th, 1901 - February 1st, 1976
Heisenberg created theory by formulating quantum mechanics in terms of matrices and discovering the uncertainty principles. Which says that a particle's position and momentum can't be both known exactly.
