# MO labelling schemes

Gold Member
2019 Award
Two different labelling schemes for MOs are shown on the left and right of this diagram:

I understand the LHS naming scheme, since the MOs are simply labelled according to the AOs from which they are derived (along with ##\sigma##/##\pi## and ##u##/##g## for the MO).

I don't understand the numbering scheme on the RHS. The book says that 'orbitals of the same symmetry are distinguished from one another by numbering them 1,2,...'. What does this mean? Thanks.

DrDu