# How do you determine how many electrons occupy the anti bonding orbitals?

For molecular orbital theory: How do you determine how many electrons occupy the anti bonding orbitals? Also, why does hydrogen gas have no anti bonding orbitals- if each atom's electrons form a molecular orbital, then their energy is reduced so where does the extra energy go ?

• Hydrogen has antibonding orbitals - just that it is unfilled. – t.c Oct 7 '14 at 19:55
• Why are they unfilled? Wouldnt the conservation of energy require an antibonding orbital and a molecular orbital to be both filled up? – user58953 Oct 7 '14 at 20:00
• Forming a bond makes the molecule more stable. So the "extra energy" is released to the system. That's the definition of an energetically favorable reaction ($\ce{H + H -> H2}$). – Geoff Hutchison Oct 8 '14 at 1:05
• Not necessarily @LDC3. The bond may just be weakened. – Dissenter Oct 8 '14 at 4:50
• @Dissenter OK, I'll clarify. If you promote an electron into an anti-bonding orbital, the bond weakens and may undergo a reaction. If the molecule obtains an electron which must go into the anti-bonding orbital, the bond will likely break, resulting in a radical. – LDC3 Oct 8 '14 at 4:53