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450
Democritus
Democritus was born in Abdera, Greece in 460BC
1.All matter consists of invisible particles called atoms. 2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement.
Democritus's theory was discredited due to the wide acceptance of aristotles idea. -
John Dalton
John Dalton, a British chemist and physicist, who lived in the 1800's, developed a theory that matter is simply composed of atoms of different weights and is combined in ratios by weight. Also proposed that these atoms are spherical, and are in motion.
1803 -
JJ Thomson
Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram. Studied "canal rays" and found they were associated with the proton H + .
Lived in the late 1800's and early 20th century. -
Ernest Rutherford
Studied radiations emitted from uranium and thorium and named them alpha and beta.
Lived in the late 1800's and early 1900's.
Made his discovery almost at the sametime as Jj Thomson.
He lived in New Zealand. -
Bohr
Bohr developed the Bohr atomic model, with electrons travelling in orbits around the nucleus, and chemical properties being determined by how many electrons are in the outer orbits. He also integrated the Planck quantum theory, stating that when electrons change orbits they emit a quantum of discrete energy. Lived in Denmark . An interesting fact is that he helped refugees during the Nazism. -
Schrodinger and Werner Heisenberg
Electrons are in constant motion around the nucleus, protons and neutrons jiggle within the nucleus, and quarks jiggle within the protons and neutrons.