# Energy level of molecular orbitals in heteronuclear diatomic compounds

I have been studying the molecular orbital theorem. I read that the energy levels for the $$\ce{p}$$ orbitals in the first series of $$\ce{p}$$ block molecules are something to the tune of $$\pi_x=\pi_y<\sigma_z<\pi_x^*=\pi_y^*<\sigma_z^*$$

except for $$\ce{O2 and F2}$$, which have $$\sigma_z<\pi_x=\pi_y<\pi_x^*=\pi_y^*<\sigma_z^*$$

But it got me thinking: what order would the orbitals take in a compound such as $$\ce{CO, NO}$$?

(Also, out of curiosity, what about $$\ce{p-p}$$ bonds in higher series of the $$\ce{p}$$ block? Does $$\ce{Cl2}$$ have the same order as $$\ce{O2}$$?)

My guess was that since in heteronuclear orbitals more electronegative elements have lower energy orbitals, compounded with the fact that the $$\sigma$$ orbitals it forms tend to be lower energy, it should follow the latter’s order.