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460 BCE
Democritus
Democritus was born in Abdera, Greece in 460BC. He lived to be 90 years old, dying in the year 370BC. He studied natural philosophy in Thrace, Athens, and Abdera, Greece.
His mentor, Leucippus, originally came up with the atomic theory, but it was then adopted by Democritus. Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms. . -
Antoine Lavoisier
Antoine Lavoisier (1743-1794) was the first person to make good use of the balance. He was an excellent experimenter. After a visit with Priestly in 1774, he began careful study of the burning process. He proposed the Combustion Theory which was based on sound mass measurements. He named oxygen. He also proposed the Law of Conversation of Mass which represents the beginning of modern chemistry. -
John Dalton
John Dalton (1776-1844) proposed the Law of Multiple Proportions. This law led directly to the proposal of the Atomic Theory in 1803. He also developed the concept of the mole and proposed a system of symbols to represent atoms of different elements. (The symbols currently used were developed by J.J. Berzelius(1779-1848)). Dalton recognized the existence of atoms of elements and that compounds formed from the union of these atoms. -
Max Planck
Max Karl Ernst Ludwig Planck was born in Kiel, Germany, on April 23, 1858. Planck's work on the quantum theory, as it came to be known, was published in the Annalen der Physik. His work is summarized in two books Thermodynamik (Thermodynamics) (1897) and Theorie der Wärmestrahlung (Theory of heat radiat ion) (1906). -
J.J Thomson
J. J. Thomson (1856-1940) identified the negatively charged electron in the cathode ray tube in 1897. He deduced that the electron was a component of all matter and calculated the charge to mass ratio for the electron.
e/m = -1.76 x 108 coulombs/g
Thomson and others also studied the positive rays in the cathode ray tube and discovered that the charge to mass ratio depended on filling gas in the tube. -
Albert Einstein
Einstein treated matter and energy as exchangeable. Albert Einstein became famous for the theory of relativity, which laid the basis for the release of atomic energy. In 1905 Albert Einstein formulates Special Theory of Relativity. -
Robert Millikan
Robert Andrews Millikan was born on the 22nd of March, 1868, in Morrison, Ill.His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity. -
Ernest Rutherford
Ernst Rutherford (1871-1937) proposed the nuclear atom as the result of the gold-foil experiment in 1911. Rutherford proposed that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. This was a very radical proposal that flew in the face of Newtonian Physics. -
Niels Bohr
In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. -
Werner Heisenberg
Scientific Contributions. Heisenberg is best known for his uncertainty principle and theory of quantum mechanics which he published at the age of twenty-three in 1925. He was awarded the Nobel Prize for Physics in 1932 for his subsequent research and application of this principle. -
Erwin Schrodinger
In 1926 Erwin Schrödinger, an Austrian physicist, took the Bohr atom model one step further. 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. -
James Chadwick
James Chadwick (1891-1974) discovered the neutron in 1932. Chadwick was a collaborator of Rutherford's. Interestingly, the discovery of the neutron led directly to the discovery of fission and ultimately to the atomic bomb. -
Marie Curie
Born Maria Sklodowska, Marie Curie (November 7, 1867 to July 4, 1934) became the first woman to win a Nobel Prize and the only woman to win the award in two different fields (physics and chemistry). Curie's efforts, with her husband Pierre Curie, led to the discovery of polonium and radium and, after Pierre's death, the further development of X-rays. -
Louis de Broglie
Louis de Broglie,(born August 15, 1892, Dieppe, France—died March 19, 1987, Louveciennes), French physicist best known for his research on quantum theory and for predicting the wave nature of electrons. He was awarded the 1929 Nobel Prize for Physics.
