Atomic structure

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Alpha-particles scattering and the nucleus

(alpha particles - smaller than atoms and had high kinetic energies) - useful in experiments to find composition of atoms.

Rutherford noticed that most of alpha particles passed through - suggesting there might be a lot of empty space in atom.

Rutherford carried out further experiments with Geiger and Marsden using gold foil.

They directed parallel beams of alpha particles at a sheet of gold foil about 100 atoms thick.

Most alpha particles passed straight through, some were deflected and 1/20000 were deflected through an angle of more than 90 degrees.

Experimental set up:

source of alpha particles encased in metal with small aperture

vacuum so no air can interfere

gold foil about 100 atoms thick

zinc sulphide screen (glows when hit by alpha particle

detector (could be moved round to detect scattered a particles at different angles

source, vacuum, gold foil, screen, detector

Most alpha particles went straight through

Some particles were deflected at a small angle

A very small number of alpha particles were deflected at angles greater than 90