with negative electrons stuck in it.
This was called the Plum Pudding model where the electrons (blue balls)
were like plums stuck in a positive pudding (red ball).
Rutherford and Marsden fired very fast a-particles
into a very thin piece of gold sheet (called gold foil).
The foil was only a few atoms thick
and most of the a-particles went straight through it to the detector.
When the detector was moved around the foil
they were surprised to find that a small number of a-particles
seemed to have been scattered in all directions.
Some of the a-particles even came back towards the emitter.
Rutherford and Marsden suggested a structure for the atom
which would account for the scattering of a-particles
(continued).
