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Atomic structure

Evidence for atomic structure

You should be able to interpret information about Rutherford's scattering experiment.

The 'plum pudding' model of the atom

Plum pudding model

The plum pudding model

An early model (scientific idea) about the structure of the atom was called the plum pudding modelplum pudding model: The scientific idea that an atom is a sphere of positive charge, with negatively-charged electrons in it.. In this model, the atom was imagined to be a sphere of positive charge with negatively charged electrons dotted around inside it - like plums in a pudding.

Scientific models can be tested to see if they are wrong by doing experiments. An experiment carried out in 1905 showed that the plum pudding model could not be correct.

Rutherford's scattering experiment

A scientist called Ernest Rutherford designed an experiment to test the plum pudding model. It was carried out by his assistants Hans Geiger and Ernest Marsden.

A beam of alpha particlesalpha radiation: Radiation consisting of alpha particles, which are each made from two protons and two neutrons, and are identical to helium nuclei. was aimed at very thin gold foil and their passage through the foil detected. The scientists expected the alpha particles to pass straight through the foil, but something else also happened.

Some of the alpha particles emerged from the foil at different angles, and some even came straight back. The scientists realised that the positively charged alpha particles were being repelledrepel: Push apart. and deflecteddeflect: To cause an object to change direction. The object is 'deflected'. by a tiny concentration of positive charge in the atom.

As a result of this experiment, the plum pudding model was replaced by the nuclear model of the atom.

Check your understanding of the experiment by studying this activity:

Back to Atoms and radiation index

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