Summary AQA GCSE Physics Combined Science - Atomic Structure Notes

ATOMIC STRUCTURE
STRUCTURE OF THE ATOM
 Typical radius of an atom: 1x10^-10m
o The radius of the nucleus is 10,000 times smaller
o Most of the mass of the atom is concentrated at the nucleus
 Isotopes: atoms of the same element, with different masses, that have the same number of
protons but a different number of neutrons




ATOMIC MODEL
 1800 – Dalton said that everything was made of tiny spheres that could not be divided
 1897 – JJ Thompson discovered the electron
o Plum Pudding Model: overall charge of an atom is neutral, so the negative electrons
are dispersed through the positive ‘pudding’ to cancel out the charges
 1911 – Rutherford realised most of the atom was empty space
o Gold Foil Experiment:
 most alpha particles went straight through the foil, meaning most of the
atom is empty space
 Some alpha particles were slightly deflected, meaning the nucleus must be
charged
 Few alpha particles deflected significantly, meaning the nucleus contained
most of the mass
 1913 – Rutherford Model: a positive nucleus at the centre and negative electrons existing in
a cloud around the nucleus
 1913 – Bohr produced the final model of the atom
o The electrons existed in fixed ‘orbitals’ to not cause the atom to collapse




RADIATION
 Activity is the rate at which a source of unstable nuclei decays, measured in Becquerels (Bq)
 Radioactive decay is a random process
 Countr-rate: the number of decays recorded by a detector per second (e.g. a Geiger-Muller
Tube)
 ALHPA
o Charge of +2
o Range of a few centimetres
o Heavy
o Stopped by paper/skin
o Highly ionising