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400
Aristole 400 B.C
Aristotle's major contribution was infultrating that all substances are made up of 4 states of matter. They were Earth, Fire, Water, and Air. With that he also made an enemy in scientist Democritus. He studied different kinds of sciences and had a realization that everything wasn't made of atoms. Aristotle was creamed and proved wrong later. -
400
Democritus 400 B.C
Democritus's major contribution was that he proposed the atom. Demnocritus and his mentor Leucippus dicovered the first atom. He thought atoms couldn't be at all tampered with. Democritus concluded that humans had atoms in their bodies as well. -
Period: 400 to
The Atomic Theory
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John Dalton 1800 AD
John Dalton's major contribution was transforming Democritus' ideas on atoms into a modern atomic model. His theory was:
1) All matter is made of microscopic particles called atoms.
2) The atoms of the same element are identical, those of different elements are different.
3) Atoms of different elements combine in small, whole number ratios to form compounds.
4) Chemical reactions involve the combinations of atoms. No new atoms are created. ( Law of simple multiple proportions). -
J.J. Tomphson 1897 AD
J.J. Tomphson did the small yet he did the big by discovering the electron. He also performed a experiment called the 'Cathode Ray Tube' to find out whether electrons were positive or negative. They were posotive. -
Robert Millkan 1909 AD
Robert Millikan's major contribution was determining the charge and mass of an electron. He conducted experiments by measuring the effect of an electric field on very small oil droplets. From the charge of the drop and the mass on the plates, he calculated the force of gravity on an oil drop. -
Rutherford 1912 AD
Rutherford made two major contributions from his Gold Foil Experiment. The nucleas is made up of mostly + charge and mass. The atom contains a positive piece at the center called the nucleas. -
Neils Bohr 1913 AD
Neils Bohr's major contribution discovered that an electron is only found in specific circular paths, or orbits, around the nucleus. He made the first model of an atom, which has still stayed around even oday. -
Sir James Chadwick 19
Chadwick confirmed the existence of neutrons in the neucleus. Now the entire atom is figured out as a modern view,
