I'm reading up on molecular orbital theory and LCAO in Ian Fleming's "Molecular Orbitals and Organic Chemical Reactions" and I don't understand the logic here:
"When there are electrons in the orbital, the squares of the c-values are a measure of the electron population in the neighbourhood of the atom in question. Thus in each orbital the sum of the squares of all the c-values must equal one, since only one electron in each spin state can be in the orbital."
I get the first part but i don't see how c values are related to spin and wouldn't total spin in an orbital equal 0? Any help would be appreciated but, since I haven't studied quantum mechanics yet, a simple as possible explanation would be best.