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465
Democritus
Sometime in 465 BC, Democritus adopted the atomic theory from his mentor Leucippus. This hyopethsis stated that atoms could not be destroyed, split it half, are invisible, are infinite, and homogenous. He also believed solid atoms were small and pointy, while liquids were large and round. -
John Dalton
In late 1803, John Dalton came up with his own atomic theory that elements were made out of tiny particles called atoms, and pure elements required all atoms to be a certain size, shape, mass, etc. He also stated that compounds are formed from a combination of 2 or more different atoms. -
J.J. Thomson
J.J. Thomson was the first to discover that atoms were made of electrons and could in fact be divided, which disproved theories before it that stated otherwise. His "plum pudding" model shows that electrons are surronded by positive charges to balance negative charges. -
Ernest Rutherford
At some point in 1911 Ernest created a model of the atom that described it as a positively charged core called the nucleusm where electrons circulate around it in a fashion similiar to the way planets orbit the sun. -
Niels Bohr
Adding onto Rutherford's theory that the atom was a nucleus surronded by electrons in orbit, Bohr also added that these electrons orbit in a circular fashion around the nucleus. He also was the first to state that the electrons travel in separate orbits. Bohr is credited with one of the most popular modern models of the atom. -
James Chadwick
Adding on as well as disproving all the atomic theories before his own, Chadwick's own theory stated that atoms have neutrally charged particles, or neutrons. He also established that the atomic number of an atom was determined by the number of protons in an atom.
