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300 BCE
Democritus
Democritus was a Greek philosopher who is credited to the creation of the first atomic theory. His theory proposed that everything is composed of atoms, which are physically, but not geometrically, indivisible. -
Billiard Ball Model
Because Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard balls, so he used wooden balls to model them. -
Billiard Ball Model
Because John Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. -
Bohr's Atom
In 1913, Niels Bohr postulated that the simplest atom, the hydrogen atom, consisted of one heavy proton in the center with one lighter electron in orbit around the proton. Bohr supposed
-electrons move in circular orbits around the atomic nucleus.
-Only certain orbits are permitted.
-That in these permitted orbits, the electrons would not radiate (would not create radio waves).
-That light of certain colors (and wavelengths) would be created when the electron (of its own power) changed orbits. -
Parson's Magneton Theory of the Atom
By 1915, A. L. Parson knew that the Bohr model of the atom could not be real, so he developed and even experimented on a model of the atom where the electrons were not point-sized particles that orbit around the atomic nucleus. In Parson's atom, the electrons in the shells surrounding the nucleus were rings of charge (with the shape of a toroid or donut). Since the electrostatic charge at the surface of the these rings is rotating, each electron is a tiny magnet. -
De Broglie
About 1924, Louis de Broglie proposed that all particles of matter (from single atoms to large objects) moving at some velocity would have the properties of a wave. Today, most physicists take this farther and say that all material objects actually are waves until they are measured or observed in some way. When this takes place, the wave is said to collapse and turn into an object. -
Dirac's Model of the Atom
The Dirac model is an equation that includes imaginary numbers. It is not an attempt to describe the objective reality of the physical electron, but to predict the various levels of energy that the electron may have at various times. Dirac won the Nobel Prize in physics with Erwin Schrodinger in 1933.
