The Bohr Atom
proposed that the atom contained a massive nucleus
containing all of its positive charge, and that the
much lighter electrons were outside this nucleus. The
nucleus had a radius about ten thousand times smaller
than the radius of the atom, only ten femtometres, or
one hundred thousand billionth of a metre!
at large angles occured when the alpha particles came
near to a nucleus. The reason that most alpha particles
were not scattered at all was that they were passing
through the relatively large 'gaps' between nuclei.
revised Thomson's 'plum pudding' model, showing how
electrons could orbit a positively charged nucleus,
like planets orbiting a sun. In 1915 Niels Bohr adapted
Rutherford's model by saying that the orbits of the
electrons were quantised, meaning that they could exist
only at certain distances from the nucleus.