I have few questions trying to understand covalent bond in the simplest molecule H2 of two Hydrogen atoms. 1. Can covalent bond be created between two hydrogen atoms for which electrons have parallel spin? That is, electron in first hydrogen atom has spin UP and electron in the second hydrogen atom has also spin UP. 2. What determines whether covalent bond will be created with bonding or antibonding state? 3. Since antibonding state has higher potential energy than the two individual neutral hydrogen atoms, then how it can ever be created? 4. This final question is about covalent bond in multielectron atoms... Say we have nitrogen molecule N2 which has 3 covalent bonds. I understand that 3 pairs of electrons in the outer (valence) shell form three covalent bonds but are inner shell involved in covalent bonding as well? That is, 1s and 2s orbitals (nitrogen electron configuration is: 1s2 2s2 2p3). I am confused about this because at first I thought that only valence electrons form covalent bonds but in my book there is a graph for this molecule that shows that beside valence bonds there are also two sigma states (one bonding marked as σ1s and one antibonding marked as σ*1s).