I wanted to ask a question about metallic bond - band electron theory.
Consider the diagram of Sodium below:
Circled are orbitals both containing $2$ electrons each which combine using LCAO to give a set of bonding and antibonding electrons.
However, the $4$ electrons involved in this bonding appear to only give $3$ electrons in the bonding and antibonding MO's produced.
This confuses me. Surely using $4$ electrons, I expect all $4$ of these electrons to also be present in the rectangle drawn.
Why are there only 3 electrons shown? Is one electron being used for the next addition of AOs?
Any answers would be greatful!