IN THE BEGINNING……In the early days of atomic theory, manyphysicists tried to explain the model of an atom.In 1902, Ernest Rutherford showed that alphaparticles emitted from the decay of unstableradioactive materials were electrically chargedhelium nuclei travelling at high speed.In 1909, Rutherford used alpha particles toinvestigate the composition of gold foil (i.e. toexplain the model of an atom).
Aim To investigate the composition of gold foil using alpha particles (i.e. to explain the model of an atom).
ResultsRutherford’s experiment found that:• Most of the alpha particles passed through thegold foil undeviated.• A few alpha particles were deflected from theirpath but continued through the gold foil.• A small number of alpha particles rebounded.
ConclusionFrom the results of his experiment, Rutherfordexplained:• As most alpha particles passed through thegold foil atoms undeviated, Rutherford concludedthat most of the atom was actually empty space.• The deviation of some alpha particlesfrom their original path were due to positive chargeswithin the foil.
ConclusionFrom the results of his experiment, Rutherfordexplained:• A small number of alpha particles hadrebounded because they collided with something muchlarger and heavier and which contains a concentratedregion of positive charge.
ConclusionAs a result of his observations, Rutherford suggestedthat the atom had a positively charged centre whichcontained most of the mass. He called the heavy positively charged centre the nucleus.He went on to suggest that the nucleus was surroundedby orbiting electrons required for electrical neutrality.
Modern measurements show thatthe average nucleus has a radiusin the order of 10-15 m. This is 100,000 times smaller than the radiusof a typical atom.