The Foundations of Chemistry

We can give the same VB description for the hybridization of the central atoms in

polyatomic ions. In NH 4 and SO 42 
, the N and S atoms, respectively, form four sp^3

hybrid orbitals directed toward the corners of a regular tetrahedron. Each of these sp^3

hybrid orbitals overlaps with an orbital on a neighboring atom (H in NH 4 , O in SO 42 
)

to form a bond.

322 CHAPTER 8: Molecular Structure and Covalent Bonding Theories

Problem-Solving Tip:Often There Is More Than One Central Atom

Many molecules contain more than one central atom, that is, there is more than one

atom that is bonded to several other atoms. We can analyze such molecules one central

atom at a time, to build up a picture of the three-dimensional aspects of the molecule.

An example is ethane, C 2 H 6 ; its Lewis formula is

H

H

HC

H

H

C H

sp^3 Hybridization occurs at the central atom whenever there are four regions of high

electron density around the central atom. AB 4 molecules and ions with no unshared

pairs on the central atom have tetrahedral electronic geometry, tetrahedral molec-

ular geometry, and sp^3 hybridization on the central atom.

Problem-Solving Tip:Use Periodic Relationships

Because F, Cl, Br, and I are all in the same group of the periodic table, we know that

their compounds would be similar. We expect that the detailed descriptions we have seen

for CF 4 would also apply to CCl 4 , CBr 4 , and CI 4 , and we do not need to go through

the entire reasoning for each one. Thus, we can say that each of the CX 4 molecules

(XF, Cl, Br, or I) also has tetrahedral electronic geometry, tetrahedral molecular geom-

etry, sp^3 hybridization on the carbon atom, zero dipole moment, and so on.

O

O

O

O

S

2–

H

H

H

H

N

H

1 s

2 p

Unshared

pairs on

O atoms are

not shown

NH 4 + SO 4 2–