Chemistry - A Molecular Science

Chapter 6 Molecular Structure & Bonding

Example 6.6 Describe the bonding in and the structure of the following ions: a) Bromate ion, BrO

1-^3

The Lewis structure of the br

omate ion shows four electron

regions around the bromine

atom, so it is sp

3 hybridized. The three O atoms form the base of this trigonal pyramidal

ion. All BrO

1- 3

bonds are single bo

nds and, therefore,

σ bonds. The O-Br-O bond angles

are ~109

o. The negative charge of the ion is distri

buted equally over all of the oxygen

atoms. The ball-and-stick and space-filli

ng models are shown in the margin.

BrO

1- 3

ion

NO

1- ion 3

SO

2- 4

ion

OBr

O

O

+2

+2 Br

O

OO

b) Nitrate ion, NO

1- 3

The Lewis structure of NO

1- has three electron groups around the nitrogen, so it is sp 3

2

hybridized and the ion is planar. The

bond is shared by all three N-O bonds, which are π

equivalent with bond orders of

4 /^3

(four shared pairs spread equally over three bonding

regions). The O-N-O bond angles are all 120

o. Resonance places the negative formal

charge equally on all of the oxygens. Posi

tively charged species bond to one of the

oxygens but not to the nitrogen. For example, addition of H

1+ to NO

1- 3

results in HNO

, 3

nitric acid, which contains an O-H bond, not an N-H bond.

O N

OO

ON

O

O

c) Sulfate ion, SO

2- 4

The Lewis structure of the su

lfate ion indicates four elec

tron regions around the sulfur

atom, so the sulfur is sp

3 hybridized. The sulfate ion is tetrahedral. The S-O bonds are all

single bonds (that is,

bonds). The O-S-O bond angles are all 109σ

o. The negative charge

on the ion is distributed equally among the ox

ygens. Note that the sum of the formal

charges is -2, the charge on the io

n. When the sulfate ion bonds to H

1+ ions to form

covalent bonds, it does so through the oxygen atoms. Thus, sulfuric acid (H

SO 2

) has two 4

O-H bonds.

OS

O

O

O

O

O

S

OO

+2

+2

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