The Changing Atom

The Changing Atom

1. Democritus

   • imagined that atoms were held together with tiny hooks
   • Suggested you could divide matter only so many times

2. John Dalton

   • All atoms of a given element are the same
   • atoms cannot be divided
   • atoms are tiny particles that make up elements
   • atoms are different in different elements

3. JJ Thomson

   • Plum-pudding model
     • negative electrons in a 'sea' of positive charge
       • = neutral with no overall charge
   • He discovered the electron

4. Ernest Rutherford

   • 2 of his students fired alpha particles at a very thin piece of gold foil
     • they measured deflection (change in direction) of the particles
   • concluded that a plum-pudding model woud hardly deflect alpha particles at all.
     • the atoms positive charge must be concentrated into a volume much smaller than the size much smalleer than itself

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