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Period: 140 to Sep 25, 1370
Democritus
-Lived from 400 BC to 370 BC
- Greek philosopher, proposed that matter was made up of small, hard, indivisible particles, which he called atoms,
-Hade no evidence to support his idea and was not widely beleived,
-Modern atomic theory begins in late 1700s -
Period: to
John dalton
-Matter is composed of tiny indivisible particls called atoms
-All atoms of the one element are identical but are not identical to other elements atoms.
-Lived in the united kingdom at first when he was born in cumbria but later then died in manchester. -
Period: to
Joseph J. Thomson
-Plum pudding model of the divisble atom
-atoms consist of uniform positive charge with also negatively charged particles
-the total positive charge of the sphere equals the total negative charge.
-Born in united kingdom in manchester but later died in cambridge. -
Period: to
Robert Milikan
-Born in Morrison, Illinois, then died in San Marino, California
-Measured charge of an electron using the atomizer which is a perfume bottle with water in it. -
Period: to
Ernest Rutherford
-Born in Brightwater, New Zealand
-Died in Cambridge, United kingdom
-Proposed a nuclear model of the atom
-Small positively charged nucleus containing most of the mass of the atom
-a very large volume around the nucleus where electrons move
-nucelas containing positively charged protons
-Protons = number of elctrons -
Period: to
Niels Henrik David Bohr
-Proposed planetary model for the hydrogen atom
-electrons move around the nucleus in a fixed orbit
-An electron can absorb energy and move to a higher energy orbit of a larger raduis
-electrons can only exist in certain discrete energy energy levels.
-Born in copenhagen, Denmark and died there. -
Period: to
James Chadwick
-The nucleus of an atom contins neutrons, electrically neutral particles with a mass similiar to that of a proton
-grew up in Bollington, united kingdom, but died at cambridge