Chemistry - The atomic structure

Chemistry - The atomic structure

1. Thompson 1897

   • ATOMS WERE NOT SOLID SPHERE'S
   • His measurements of charge and mass shwoed
     • An atom must contain even smaller negatively charged particles (electrons)
       • Beams of cathode rays changed direction in electric and magnetic fields

2. Dalton 1803

   • Daltons model was detailed it explained evidence from the experiment of gases:
     • SOLID ATOM MODEL (SPHERE)
     • All atoms of an element are identical
       • Different element contains different types of atoms
         • Atoms are neutral over all

3. Rutherford 1909

   • Rutherford and his students pointed charged particles called alpha particles at a thin gold foil
     • They expected the particles to go straight through the foil
       • Most did but other changed direction
         • He explained - a atom has a POSITIVELY CHARGED NUCLEUS containing most of its mass. it is surrounded by a 'cloud' of NEGATIVELY CHARGED PARTICLES

4. Bohr

   • Scientists realised the 'cloud' around the nucleus of an atom (RUTHERFORD'S IDEA) would be attracted to the nucleus causing the atom to collapse
     • Bohr suggested ELECTRONS ONLY EXIST IN FIXED ORBITS OR SHELLS and not anywhere in between . Each shell has a fixed energy
       • BOHR'S THEORY WAS BACKED UP WITH EXPERIMENTS

5. The electrons are contained in shells

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