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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 erased or destroyed. Democritus thought that humans had atoms in their bodies, too. -
400
Aristotle 400 B.C
Aristotle's major contribution was stating that all substances sre made up of 4 states of matter. They were Earth, Fire, Water, and Air. He found Democritus a threat and biggest rival. He studied various sciences and believed that everything wasnm't made of atoms. Aristotle was proved wrong later. -
Dalton 1800's
Dalton transformed Democritus's ideas on atoms into a scientific theory.
1. All matter is made of tiny charged particles called atoms.
2. The atoms of the same element are identical.
3.Atoms of different elements combine in small,whole number ratios to form compounds.
4. Chemical reactions involve the bonding of atoms. No new atoms are created or destroyed. (Law of the Conservation of Matter) -
J.J Thomson 1897
J.J Thomson's major contribution discovered the electron. He conducted the Cathode Ray Tube Experiment. By adding a magnetic field he found that the moving pieces were negative. His Plum Pudding Model experiment displays electrons embedded in a positive ly charged material. -
Millikan 1909
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
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.