I have a few questions on molecular orbital theory which I hope you guys can help me settle! So I understand orthogonality meaning that the molecular orbitals have zero overlap, due to the Pauli Exclusion Principle. How do a 2s and 3s molecular orbital achieve orthogonality? Is it due to a node? Does the 3s electron density penetrate the inner 2s at all? And how do 2p and 2s orbitals achieve orthogonality?