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400
Democritus 400BC
Democritus major contribution was that he proposed the atomic theory.He published over 70 books, enjoyed travelling and visited many places. He lived for 90 years and died in 370 BC. -
400
Aristotle
Aristotle major contribution was that he stated that all substances are made of 4 elements.
The 4 elements are
1)Earth
2)Fire
3)Water
4)Air -
John Dalton
John Dalton's major contribution was that he transformed Democritus ideas on atoms into a modern atomic theory. Dalton's theory was
1)All matter is made of tiny microscopic particles called atoms.
2)The atoms of the same element are identical, those of diferent elements are different.
3)Atoms of different element combine in small, whole ratios to form compounds.
4)Chemical reactions involve the combinations of atoms. No new atoms are created (Law of simple multiple proportions) -
J.J.Thompson
J.J.Thompson major contribution was that he discovered the electrons.Thompson conducted the" Cathode Ray Tube "experiment. In the"Cathode Ray Tube" experiment Thompson thought that by adding postive charge the moving pieces were negative charge. Thompson also made a model called "Plum Pudding". The model displays electrons set in a sphere of postive material. -
Robert Millikan
Robert Millikan major contribution was that he determined the mass and charge of the electron. Robert conducted oil drops by measuring the effect of an eletric field on very small oil droplets. He also conducted the mass of the drop and the charge on the plates, he even calculated the charge on an electron. -
Ernest Rutherford
Ernest Rutherford major contribution was that he discovered the nucleus. Rutherford made 2 major coclusions from his Gold Foil Experiment. The 2 major conclusions are
1)The nucleus is made up of mostly postive charge.
2)The atom contains a postive piece at the center. -
Neils Bohr
Neils Bohr major contribution was that he proposed that an electron is found only in specific circular paths, or orbit around the nucleus. Bohr's model is referred to as planetary model because eletrons move around the nucleus like the planets around the sun. -
Sir James Chadwick
Sir James Chadwick major contribution was that he confirmed the existence of neutron in the nucleus. Chadwick said
1)The atom is mostly empty space.
2)The atom consists of 2 regions.
3)Nucleus is in the center and contains protons and neutrons.
4)The electron cloud is the region where eletrons in areas of high probability called atomic orbital.
