A semi-empirical method that eliminates three- and four-center two-electron integrals is named for the “neglect” of one form of this phenomenon. For the H2+ (“H-2-plus”) ion, a pair of energies are given by “H-AA plus H-AB over quantity one plus” a measure of this phenomenon. Roothaan (“ROTE-hahn”) simplified the Hartree–Fock method into the equation “FC equals SC epsilon,” where S is a matrix named for this phenomenon. (10[1]-5[1])For two (10[1])wavefunctions, this phenomenon is described by the integral (-5[1])over all volume of “psi-A-star times psi-B,” (10[1]-5[1])which vanishes for orthogonal orbitals like p-x and p-y. A pair (10[1])of atomic orbitals (-5[1])for which this phenomenon (-5[1])is higher will have more stabilized (-5[1])bonding molecular (10[1])orbitals. (10[1])Sigma bonds form when this phenomenon (-5[1])is (10[1])end-on. (10[1]-5[1])For 10 points, (10[1])name this phenomenon (-5[1])in which (10[1])space is shared (10[1])by (-5[1])two orbitals. (10[2])■END■ (10[9]0[24])