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400
Democritus (years in BC)
the general idea that all mater is made up of atoms came from democritus. the greek word atomos (or atom) means indivisible. he also believed that in addition to being really tiny, they were solid and indestructible. -
500
Aristotle (years now in AD)
aristotle actually dismissed the earlier greeks atomic theory and many europeans thus discredited it and saw it as a lie -
John Dalton
the first modern model of the atom, john theorized that chemical elements were composed of atoms, atoms of the same were identical in mass, atoms of a different element were not the same mass, and atoms only combined in whole nuber ratios -
J.J. Thomson
J,J Thomson was the first to discover the electron within the atom. he proposed that the electrons were studded on to a large, positively charged sphere. -
Max Planck
Planck explained that energy is not a continuous, flowing entity, but is carried in tiny, discontinuous units, which he named quanta and each quantum's energy is equal to the frequency of radiation multiplied by the universal constant which Planck defined. -
Robert Millikman
he conducted an oil drop experiment that determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. -
Ernest Rutheford
Ernest rutheford challenged Thomsons theory and came up with his own: there is a large nucleus with electrons surrounding it and orbiting it. he figured this because when he shot a particle emitter through gold foil, he found that some bounced back, proving there was a dnese center that they were bouncing off of. -
Niels Bohr
Bohr had studied under Thomson and rutheford and theorized that the electrons were in multiple layes making 'shells' and that they could determine the chemical proporties of elements. Bohr's discovery came to be the basis for quantum mechanics in the 1920s -
electron cloud model.
Erwin Schrödinger and Werner Heisenberg proposed this model that says there are not specific shells like in Bohr's model, but there is a general area in which they can appear most often. -
James Chadwick
James chadwick, an English physicist, discovered with Rutheford that the dense nucleus of an atom consisted of protons and neutrons, and that all atoms contain at least one proton.
