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400
400 B.C. Democritus
About 400 B.C. the greek philospher demoritus suggested that all matter was formed of different types of tiny discrete particles and that the propertieso f these particles al so determined the porperties of matter. -
John Dalton
Daltons atomic theory consisted of: All matter is made of atoms. Atoms are indivisible and indestructible. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms. A chemical reation is a rearrangement of atoms. -
J.J. Thomson
In 1879, J.J. Thomson discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. -
Rutherford
By 1911 the components of the atom had been discovered. The atom consisted of subatomic particles called protons and electrons. However, it was not clear how these protons and electrons were arranged within the attom. J.J. Thomson suggested the "plum pudding" model. In this model the electrons and protons are uniformly mixed throughout the atom. -
Neils Bohr
A student of Ruthford's developed a new model of the atom. He proposed that the electrons are arranged in a concentric cercular orbits around the nucleus. -
Current Atomic Theory
The idea that all matter is made up of atoms. Those atoms are made up of tiny sub-atomic particles called protons, neutrons, and electrons.