development of atom model

• 1st discovery- ancient greeks-  all matter was made of a combination of substances called 'elements' Later Greek thinkers suggested that matter could be made up of invisible particles, called these particles atoms but they had no experimental evidence for their model.
• 2nd discovery - john dalton (1803) - he proposed the first modern atomic theory
• Dalton’s model included these ideas:

  • atoms cannot be broken down into anything simpler
  • the atoms of a given element are identical to each other
  • the atoms of different elements are different from one another
  • the atoms of different elements join to make compounds
  • during chemical reactions atoms rearrange to make different substances
• 3rd discovery - JJ thompson- discovery of electrons-Atoms can be broken down into smaller parts. An atom is made of tiny negatively charged electrons dotted about a positively charged sphere like a plum pudding.
• rutherford- 1909-1911- discovered some positively charged particles fired at gold foil bounced back when they were expected to pass straight through.
• rutherford-atoms have a central positive nucleus. Most of the mass of an atom is found in the nucleus.