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Period: 450 BCE to 379 BCE
Democritis discovers Atoms
About 400 B.C. the Greek philosopher Democritus suggested that all matter was formed of different types of tiny discrete particles and that the properties of these particles also determined the properties of matter. -
330 BCE
Aristotle
Aristotle did not believe that matter was made up of tiny particles called atoms, but rather matter up of five basic elements, earth, water, air, fire, and ether. Although Aristotle's idea wasn't correct, his idea was more widely accepted than Democritus's idea from about 2000 years. -
Antoine Lavoisier
In 1789, Antoine Lavoisier grouped the elements as simple substances (gases), metals, non-metals, and earthly simple substances based on their physical and chemical properties. Gases included light, oxygen, and hydrogen. Non-metals were identified by their ability to oxidize and convert into acidic substances. -
John Dalton
A theory of chemical combination, first stated by John Dalton in 1803. It involves the following postulates: (1) Elements consist of indivisible small particles (atoms). (2) All atoms of the same element are identical; different elements have different types of atom. (3) Atoms can neither be created nor destroyed -
J.J Thomaon
Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson's plum pudding model of the atom had negatively-charged electrons embedded within a positively-charged "soup."