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Sep 19, 1000
Democritus
theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained. This piece would be indivisible. He named the smallest piece of matter “atomos,” meaning “not to be cut.” -
John Dalton
certain gases only could be combined in certain proportions even if two different compounds shared the same common element or group of elements. The father of the atomic theroy -
J.J. Thomson
the first to suggest that the fundamental unit was over 1000 times smaller than an atom, suggesting the subatomic particles now known as electrons. -
Albert Einstein
Proved that e=mc squared -
Robert Millikan
carefully studying individual droplets, Millikan was able to show that the charge on a drop was always an integral multiple of a small, but finite value. When his data are converted to SI units, the charge on a drop is always some multiple of 1.59 x 10-19 C. -
Ernest Rutherford
the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.
Picture- Descrbing positive charged nucleus with nergtive electrons -
Neils Bohr
Introduced the Bohr model
Shows the atom that positivly charged
Also shows electrons travel in circular orbit around the nuecules -
Louis de Brogile
Stated: electrons could behave as waves under some conditions, a finding that helped scientists understand that the atom didn't behave like the solar system because electrons do not move in regular orbits. -
Wolfgand Pauli
with two possible values, in order to resolve inconsistencies between observed molecular spectra and the developing theory of quantum mechanics. He formulated the Pauli exclusion principle, perhaps his most important work, which stated that no two electrons could exist in the same quantum state, identified by four quantum numbers including his new two-valued degree of freedom -
Werner Heisenberg
created matrix mechanics, the first version of quantum mechanics in 1925.
Discovered Uncertainty Principle. He said this means that electrons do not travel in neat orbits. Also, all electrons that contain photons will then change momentum and physics. -
Erwin Schrödinger
took the Bohr atom model one step further. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position.
Picture- Quantum mechanical model -
James Chadwick
He proved existence of the neutron
