system
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human
Does a filled anti-bonding orbital signify a lone pair?

I was just wondering what these electrons were doing, if they weren't bonding. I mean I know they are anti-bonding, but are they also technically lone pairs since they don't bond to anything?
gpt
Electrons don't really 'do' anything. They just occupy orbitals. Some of which have density in-between the two atoms and are thus called bonding, and some which don't (for symmetry reasons) and are thus anti-bonding. 

An anti-bonding orbital doesn't necessarily correspond to a lone pair. And you'll liable to get confused more than anything if you mix Lewis theory with MO theory.

Look at HF and the fluorine atom, then its 2s electrons and four of its p-electrons don't participate in bonding. You have one sigma bonding orbital that's occupied and four _non-bonding_ orbitals, which are neither bonding or antibonding, but essentially still atomic orbitals as there's little overlap. It's a similar story with water, where one p orbital and the 2s orbital are non-bonding, while the other two p-orbitals are bonding to water.