C4- Development of the atomic theory

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Dalton

developed an atomic theory in the 1800s

he described atoms as solid spheres. different ones are made up of different elements.

his conclusions:

  • all matter is made of atoms
  • atoms cannot be broken down into anything simpler
  • in a chemical reaction, atoms are rearranged
  • all atoms of the same element are the same
  • compunds form when two or more different atoms join

HIS THEORY WAS DEVELOPED BY MANY OTHER SCIENTISTS

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Thompson

discovered te electron in 1897

showed Dalton was wrog. Made Plum pudding model

the atom was imagined as a sphere of positive charge with negatively charged electrons dotted around inside, rather like plums in a pudding. An experiment was carried out in 1905 to support this 'plum pudding' model of the atom

  • dalton thought atoms couldnt be simplified
  • Thompson used measurements of charge and mass to prove electrons existed
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Rutherford

discovered the atom contained a nucleus in 1911

he found:

  • more evidence that showed the atom contained smalle pieces
  • thought most of the atom was empty space
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Rutherford & Geiger+Marsden

GOLD FOIL EXPERIMENT

WHAT HAPPENED:

  • Rutherford tested plum pudding model
  • fired alpha particles at thin gold foil
  • they expected particles to pass straight through
  • some particles emerged at different angles and some cam straight back. this showed the positive alpha particles were being repelled by the positive nucleus .

PROVED PLUM PUDDING MODEL WRONG

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Bohr

supported Rutherfords atom model

showed electrons contained in shells

each shell had a fixed energy

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