John Dalton

John Dalton's atomic theory was the first comprehensive attempt to explain all matter regarding atoms and their properties. Dalton's theory included the following postulates:

• Indivisible atoms

  All matter is made of indivisible atoms and cannot be created or destroyed.

• Identical atoms of the same element

  Atoms of the same element are identical in size, mass, and other properties.

• Different atoms of different elements

  Atoms of different elements differ in size, mass, and other properties.

• Compound formation

  Atoms of different elements can combine in simple whole-number ratios to form chemical compounds.

• Chemical reactions

  Chemical reactions are the result of atoms being combined, separated, or rearranged.