The Atom

The Atom

1. John Dalton

   • All matter is made up of tiny particles called atoms.
   • Atoms are indivisible.
   • atoms cannot be created or destroyed

2. William Crookes

   • conducted experiments with a glass tube
   • negative electrode= cathode
   • positive electrode= anode
   • gas at low pressure high voltage
   • cathode rays = negatively charged

3. J.J.Thopmson

   • Cathode rays were attracted by the positive plate in an electric field
     • Had a negatitive charge
   • Measured the ratio of charge to mass for the particles (e/m)
   • plum pudding model of the atom - inadequate

4. Robert Milikan

   • Oil drop experiment
     • sprayed tiny droplets of oil between two charged metal plates.
   • Determined the size of the charge on the electron.

5. Ernest Rutherford

   • Assitants; Geiger and Marsden
   • Fired alpha particles at a very thin gold foil
   • Most of the alpha particles were not deflected al all, they had passed through basically empty space.
   • Some particles were deflected at small angles
   • a small number of particles were deflected at angles greater than 90 degrees
   • a very small number actualy bounced back towards their source.
   • being repelled by a dense concentration of positive charge
   • positively charged central region called the nucleus.

6. James Chadwick

   • discovered the neutron.