Superposition/electron energy levels

[granpa]

when an electron in an atom transitions from one shell to another does it do it instantly or is there a time when it is partially in one and partially in the other. in other words in a superposition of both states.

 

[malawi_glenn]

In the framework of time-dependent perturbation theory, yes, the state will be a superposition of states, and there is a probability for it to decay to the ground state each unit time.