How many electrons can occupy a single orbit?

Answer 1

Electrons orbiting an atomic nucleus do not do so like planets round the sun, they do so in shells round the nucleus.

Each electron shell can accommodate 2n2 electrons, i.e. the first shell can accommodate 2 electrons, the second shell 8 electrons, the third shell 18 electrons, etc.

Electrons always fill the smallest shells (nearest the nucleus) first as this is the lowest energy configuration.

The shells do not have to be full - for instance a hydrogen atom has just one electron and thus the first shell has only one electron in it not two.

It is possible to push an inner electron up into a higher shell (by providing energy) if there is a vacancy - however it will fall back and when it does so it will emit a photon of light this is why things glow when they get hot.

Answer 2

2