where A1s is a 1s-orbital centered on one atom (A) and B1s is a 1s-orbital centered
on the other atom (B). The technical terms for adding together wavefunctions
(sometimes with different weighting coefficients) is called “forming a linear combination,”
and the molecular orbital in Eq. 1 is called a linear combination of
atomic orbitals (LCAO). A molecular orbital formed from a linear combination of
atomic orbitals on different atoms is called an LCAO-MO. Note that at this
stage there are no electrons in the molecular orbital: a molecular orbital is just
a combination—in this case, a simple sum—of wavefunctions. Like atomic orbitals,
the molecular orbital in Eq. 1 is a well-defined mathematical function that can
be evaluated at each point in space and pictured in three dimensions.