For instance, in h1 the s- and p-or

For instance, in h1 the s- and p-orbitals all have their usual signs and their amplitudes
add together where they are all positive. In h2, however, the signs of px and
py are reversed, and so the resulting interference pattern is different.
The four hybrid orbitals that we have constructed differ only in their orientation,
with one pointing toward each corner of a tetrahedron (FIG. 4.13); in all other
respects, they are identical. These four hybrid orbitals are called sp3 hybrids because
they are formed from one s-orbital and three p-orbitals. In an orbital-energy diagram,
we represent the hybridization as the formation of four orbitals of equal
energy. That energy lies between the energies of the s- and p-orbitals from which
the hybrid orbitals are constructed (37). The hybrids are colored green to remind
us that they are a blend of (blue) s-orbitals and (yellow) p-orbitals. An sp3 hybrid
orbital has two lobes, but one lobe extends farther than those of the contributing
p-orbitals and the other lobe is shortened. The fact that hybrid orbitals have their
amplitudes concentrated on one side of the nucleus allows them to overlap more
effectively with other orbitals, and as a result the bonds that they form are stronger
than in the absence of hybridization.
We are now ready to account for the bonding in methane. In the promoted,
hybridized atom, each of the electrons in the four sp3 hybrid orbitals can pair with
an electron in a hydrogen 1s-orbital. Their overlapping orbitals form four _-bonds
that point toward the corners of a tetrahedron (FIG. 4.14). The valence-bond
description is now consistent with experimental data on molecular geometry.
When there is more than one “central” atom in a molecule, we concentrate on
each atom in turn and match the hybridization of each atom to the shape at that
atom predicted by VSEPR. For example, in ethane, C2H6 (38), the two carbon