Atomic Theory

Democritus

442 BCE

Democritus was a Greek philosopher and scientist who first proposed the theory that matter is comprised of minuscule particles that he called "atomos." He created the first atomic model, which depicted atoms as having no structure, solid, and differing in size, shape, mass, position, and arrangement.

John Dalton

1803

John Dalton was an English physicist, chemist, and meteorologist who, in 1803, introduced an atomic model wherein the atoms are solid, spherical, and have measurable mass.

Michael Faraday

1830

Faraday was a British physicist whose experiments with electrodes introduced the idea that atoms have electrical properties

Henri Becquerel

1896

Henri Becquerel was a French physicist who discovered the existence of radioactivity. He did so by performing experiments with uranium and other substances.

J.J. Thomson

1897

J.J. Thomson was an English physicist who first discovered the electron. He did so by using a cathode ray tube to demonstrate how the current model of an atom did not account for both positive and negative charges. Thomson then proposed his plum pudding model of the atom.

Ernest Rutherford

1911

Ernest Rutherford was a British physician who happened to be a former student of J.J. Thomson. Rutherford proved Thomson's plum pudding model incorrect with his gold foil experiment, which proved that an atom has a nucleus- in which a few, dense positive charges are housed with the electrons surrounding it.

Niels Bohr

1913

Bohr was a Danish physicist who proposed an improved atomic model wherein the electrons are arranged in concentric orbits around the nucleus. Bohr likened this model to the solar system, and so, it is thought of as the planetary model.

Werner Heisenberg

1925

Heisenberg was a German theoretical physicist, and he is known for developing the uncertainty principle, which stated that it is impossible to discern both the exact speed and location of electrons. This led to the modern quantum model of the atom.

Erwin Schrödinger

1926

Schrodinger was an Austrian physicist that developed the quantum mechanical model, which helps to predict the location of an electron.

James Chadwick

1932

James Chadwick was a British physicist who discovered the presence of neutrons within the nucleus.

Murray Gell-Man & George Zweig

1964

These two men proposed the theory of "quark" flavors.