Atomic structure

Atomic structure

Plum Pudding model
1. It was previously believed atoms were the smallest particles that existed
2. In 1804 Dalton agreed with Democritus, that matter was made up of atoms which couldn't be broken up but he thought each element was made of a different type of atom
  1. In 1897 J.J Thompson discovered tiny, negatively charged particles(electrons) and that atoms can give out electrons so Dalton's theory was slightly wrong as atoms could be broken up
    1. Thompson suggested atoms were spheres of positive charge with tiny negative electrons stuck in them - like plums in a plum pudding
      1. However the 'plum pudding' theory didn't last long as in 1909 Rutherford and Marsden fired a beam of alpha particles at thin gold foil, a slight deflection of the positive alpha particles was expected to be caused by the electrons in the 'plum pudding' model
        However - most alpha particles just went straight through with the odd one coming straight back at them, which was a bit of a shocker
        Rutherford and Marsden realized this meant most of an atoms mass was in its centre in a tiny nucleus they also realized the nucleus must have a large positive charge since positive alpha particles were repelled at such large angles
        The experiment also showed that most of an atom is just empty space which was also shocking as atoms make up everything
        In short Rutherford concluded: Most an atom is empty space, Most of an atoms mass is compressed into a tiny central volume called a nucleus and that an atoms nucleus has an overall positive charge
        Rutherford and Marsden came up with the nuclear model of the atom
        Nucleus is tiny but makes up most the atoms mass, it contains protons(positive charge) & neutrons(neutral charge) so overall positive charge on nucleus
        The rest of the atom is mostly empty space
        Negative electrons whizz round the outside of the nucleus and give the atom its overall size
        atoms have no overall charge an electrons charge size is the same as a protons but opposite
        This means the number of protons and electrons is always equal in a neutral atom
        If electrons are added or removed the atom becomes a charged particle called an ion

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	Created by Jack Willepotte about 8 years ago