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442 BCE
Democritus
Democritus was born in 460 BC in Greece. He reasoned that if you cut something in half, you would eventually reach a piece so tiny that it could not be cut. He stated that all matter consists of invisible particles he called atoms. Some people actually question whether or not he deserves credit for the atomic theory. -
John Dalton
Dalton was born on either September 5 or 6, 1766, in Eaglesfield, England. He proposed that all matter was composed of atoms. He believed that they were invisible and indestructible building blocks of life. He started teaching at his Quaker school at 12 years old. -
Cathode Ray Tube Experiment
JJ Thomson discovered the electron - an electric current is created through a container with a vacuum, which create visible rays called cathode rays, Thomson said these rays were made of particles, which he called corpuscles (now electrons), and that these particles were present in all kinds of matter. -
J.J. Thomson
Thomson was born on December 18, 1856, in Cheetham Hill, England. Through an experiment with cathode rays, he discovered electrons and created his Plum Pudding Model. He also came to head the Cavendish Laboratory at Trinity College in Cambridge. -
Gold Foil Experiment
Ernest Rutherford discovered the nucleus - he directed alpha particles at a piece of gold foil, he recorded only a small number of the particles were deflected off of the foil and he proposed the deflection of the particles was because of the atom’s nucleus. -
Robert Millikan
Millikan was born on March 22, 1868, in Morrison, Illinois. He discovered the size of the charge on an electron. He discovered this through his Oil Drop experiment. Millikan was also Vice-Chairman of the National Research Council during World War 1. -
Oil Drop Experiment
This was an experiment by Millikan to determine the size of an electron's charge. He was able to calculate the force of gravity on the drop, and in turn, calculate the charge the drop must have. -
Ernest Rutherford
Rutherford was born on August 30, 1871, in Nelson, New Zealand. In 1911, he discovered that atoms have a nucleus surrounded by electrons by his gold foil experiment. He developed a model of the atom called Rutherford Model. The element "rutherfordium" was named after him. -
Niels Bohr
Bohr was born on October 7, 1885, in Copenhagen, Denmark. In 1912, he discovered that electrons can only occupy separate orbits, which he used to create the Bohr Atomic Model. He found that electromagnetic radiation was only emitted from atoms when an electron moved to lower energy or orbit. He also founded Copenhage Institute for Theoretical Physics and had an element, Bohrium (Bh), named after him. -
Erwin Schrodinger
Schrodinger was born on August 12, 1887, in Vienna, Austria. He had no children, but raised 2 children of other families with his wife. He created Schrodinger's equation, which accurately calculated the energy levels of electrons in atoms. -
James Chadwick
Chadwick was born on October 20, 1891, in Manchester, England. In 1932, he discovered the neutron. He was tasked with tracking evidence of Rutherford's tightly bound neutron. He discovered that when bombarded with alpha particles, beryllium emitted a stream of radiation. This stream was composed of particles that were discovered to be neutrons. For this discovery, he won a Nobel Prize in 1935
