History of Atomic Theory

Democritus

415 BCE

Greek philosopher born in 460 BC and died in 370 BC in Abdera, Thrace. He theorized that everything was composed of "atoms". He believed that atoms were indestructible and have always been and will always be in motion. He believed atoms were all made of the same material but were different shapes and sizes. He also believed atoms were infinite in number and capable of joining together.

John Dalton

1803

He lived from 1766 to 1844, He lived in England and is known as the pioneer for the modern atomic theory. Came up with Atomic Theory, on the idea that everything is made of atoms, all atoms in an element are identical, atoms of different elements vary in shape and size. He came up with the law of multiple proportions which states that if elements form more than one compound, then the ratio of the masses of the second element when combined with the first, will be a small whole-number ratio.

JJ Thomson

1897

Born in England on December 8, 1856, and died on August 30, 1940.
JJ Thomson is credited for finding the electron.
Studied cathode rays.
Published 13 books and more than 200 papers.
Developed the plum pudding model of the atom.

Robert Millikan

1909

He lived from 1868 to 1953, he lived in the U.S. He is famous for determining the charge of a single electron. He did this by using the oil drop experiment, this helped him prove the atomic structure of electricity. He also did some work on the photoelectric equation. He went to Germany for a year to study at the University of Berlin. In 1923 he won a Nobel Prize for his discoveries.

Ernest Rutherford

1911

Born in Spring Grove, New Zealand on August 30, 1871, and died on October 9, 1937. British physician who came to be known as the father of nuclear physics. In 1911, he discovered that atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons (called the Rutherford model). This was proven by his Gold Foil Experiment.

Niels Bohr

1913

Danish physicist born on October 7, 1885, in Copenhagen, Denmark and he died on November 18, 1962, in Copenhagen. Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve around the atomic nucleus but can jump from one energy level to another. During the 1930s, he helped refugees from Nazism.

Erwin Schrodinger

1921

Austrian physicist who lived in Vienna, Austria between August 12, 1887, and January 4, 1961. He developed a number of fundamental results in the field of quantum theory. He invented the Schrodinger equation which provides a way to calculate the wave function of a system and how it changes dynamically in time. This equation was used to develop the Quantum Mechanical Model. He lost his job in 1938 because he opposed Nazism which was popular at the time, so he fled to Italy.

James Chadwick

1932

He was born October 20, 1891, Manchester, England and died on July 24, 1974, Cambridge, Cambridgeshire. He was a British physicist who discovered the neutron in 1932 by using his neutron chamber in his experiments. He was also the head of the team that worked on the Manhattan Project during WW2. He was knighted in Britain for his achievements in physics.