How many electrons in an orbital?

[Jules18]

I've always been confused about how many electrons are in an orbital ... is it one, or two?

Because orbital diagrams would lead me to believe there were two, since there are two arrows on each line, but illustrations make me think otherwise.

Thanks ahead of time

 

[diazona]

There is one electron in each quantum state.

In the orbital diagrams that show two electrons in an orbital, each of those orbitals actually represents two quantum states. Spatially, the two states (wavefunctions) have the same "shape," but their electron spins are pointing in opposite directions.

 

[Phrak]

To supplement diazona, by definition an atomic orbital can accommodate 2 electrons of opposite spin.