Molecular orbital theory of heterodiatomics?

[Justhanging]

Homework Statement

What determines the order of the Molecular orbitals in heterodiatomics?

The Attempt at a Solution

In my book, I have NO with an order of

1s 2s 3s 1p 2p 4s

Where s means sigma and p means pi.

Also sometimes I see in the book the ordering being 1sigma, 1sigma*(antibonding) instead of 1sigma, 2 sigma like in NO. Is this difference caused by homodiatomics versus heterodiatomics?

I know the order of homodiatomic MO but I don't know how to find it for heterodiatomics. Can someone clarify this? Maybe its a convention or something.

 

[Justhanging]

I need straightforward answers not Quantum Mechanics.