How can you tell when atoms bond based on the valence electrons?

Answer 1

If I understand the theory correctly, then it is safe to assume that any molecular bond is based on the valence system. Valence bonding occurs when orbitals of electrons are slightly overlapped. Your question should rather be 'what kind of valence bond occured in the bond. There are 2 types namely sigma and pi. Sigma bonds occur when the orbitals of two shared electrons overlap head-to-head. Pi bonds occur when two orbitals overlap when they are parallel (wikipedia). So it is safe to assume that any bond that is covalent can be described using valence theory.