Why an atom can have nonzero toal angular momentum in the ground state?

1. Aug 24, 2012

wdlang

In its ground state, an atom has no net electric dipole momentum ,but it can have a nonzero angular momentum.

Is this a spontaneous symmetry breaking?

why the ground state is not of zero angular momentum?

2. Aug 24, 2012

Staff: Mentor

A classical, charged, rotating ring has no dipole moment, but nonzero angular momentum.
Why do you expect something special to get the same in quantum mechanics? There are orbitals with angular momentum, and if there are is a single electron in one of those orbitals you get a nonzero total angular momentum.

3. Aug 24, 2012

wdlang

intuitively, a non-rotating state is lower in energy than a rotating one

4. Aug 24, 2012

Staff: Mentor

Well, this is not true in quantum mechanics, at least not in general. And if the low-energy states with zero angular momentum are filled, electron have to use some with angular momentum.