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430 BCE
Democritus
Democritus was a Greek philosopher who was born in c. 460 BCE and died c. 370 BCE. Democritus predicted the existence of the atom (then called atomos meaning indivisible) around 430 BCE. He believed that the atoms were solid, hard, indestructible, incompressible, and uniform in size. He worked as a famous disciple under Leucippus. -
John Dalton
Born on September 5,1776 died on July 27,1844. John Dalton proposed Atomic Theory. The theory had 5 points: "Matter is made up of atoms that are indivisible and indestructible.
All atoms of an element are identical.
Atoms of different elements have different weights and different chemical properties.
Atoms of different elements combine in simple whole numbers to form compounds.
Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged." (John Dalton) -
J.J Thomson
Joeseph John Thomson ( Born: December 18, 1856, Died: August 30, 1940. made the discovery of the electron in 1897 which described that, "all matter, whatever its source, contains particles of the same kind that are much less massive than the atoms of which they form a part. They are now called electrons." He promptly won a Nobel Prize award for his brilliant discovery. He was knighted in 1908. -
Robert Millikan
Robert Andrews Millikan was born on March 22, 1868 and died December 19th, 1953. His contribution to atomic theory consisted of determining the charge of an electron using the falling-drop method. This was an oil drop suspended using the electrostatic force to find the charge needed to balance it, then he let the drop fall and found its weight from its drag through air. From there he could find the charge of the electron. In his meantime from physics, he was an author, with 10+ books published. -
Ernest Rutherford
Ernest Baron Rutherford (August 30, 1871-October 19, 1937) made his discovery in 1911, "Rutherford described the atom as having a tiny, dense, and positively charged core called the nucleus. Rutherford established that the mass of the atom is concentrated in its nucleus. The light, negatively charged, electrons circulated around this nucleus, much like planets revolving around the Sun." (Primary Connections: Linking Science with Literacy) He is the fourth of twelve children -
Niels Bohr
Born on October 7, 1885 and died on November 18, 1962, Niels Henrik David Bohr was a fantastic contribution to atomic theory. As a theoretical physicist, he worked out the problems with the Rutherford model and has established the model now used in schools all around the world, which puts electrons in their electron shells. Three of his sons turned out to be disappointments, following chemical engineering, law school, and M.D. His fourth son, Aage Bohr, earned a Ph.D. in theoretical physics. -
Werner Heisenberg
Werner Karl Heisenberg, born on December 5th, 1901 and died on Febuary 1, 1976, is considered the father of quantum mechanics. As a genius theoretical physicist, he made the statement that neither position nor momentum could be determined simultaneously without error. And that the electron shells as said by Niels Bohr could not possibly exist. But rather act as a cloud of electrons. In addition to his many doctorates, he was a classical music fan and was a distinguished pianist. -
James Chadwick
Sir James Chadwick was born on October 20, 1891 and died July 24, 1974 he is most well known for his discovery of the neutron in 1932. In 1945, Chadwick was knighted. -
Erwin Schrödinger
Erwin Rudolf Josef Alexander Schrödinger, born on August 12, 1887 and died on January 4, 1961, earned his Ph.D. in 1910 in theoretical physics. His contribution to atomic theory was praised in 1933 with the Nobel Prize. This contribution was the groundbreaking Schrodinger Wave equation, which predicts the way electrons progress through time as particle-waves. He also wrote a book trying to combine quantum physics with genetics, called "What is Life?"