Chemistry Reference
In-Depth Information
EXAMPLE 5.18
NO
3
Draw an electron dot diagram for the
ion.
Solution
The number of shared electrons is
32
24
8.
Here is the structure with only
Valence
Valence
the shared electrons shown:
electrons
electrons
Atoms
available
required
O
N
O
N
5
8
(Incomplete
)
3 O
18
24
O
Negative
charge
Here is the structure showing all the electrons:
1
Total
24
32
O
N
O
O
The double bond was arbitrarily placed between the nitrogen atom and the oxy-
gen atom below it. However, there is no difference between that oxygen and
the one to the left of the nitrogen atom or the one to its right. We could draw
the double bond between nitrogen and either of those atoms instead. All the fol-
lowing structures are equivalent:
O
N
O
O
N
O
O
N
O
O
O
O
In fact, the extra pair of electrons spends some time in each of the three posi-
tions, and the structures are said to be
resonance structures
of each other. Note
that in each one, all the
atoms
are in the
same positions;
only the electrons have
changed positions.
Practice Problem 5.18
Draw all resonance structures for the
NO
2
ion.
Hydrogen atoms very often bond with oxygen atoms but seldom bond with
oxygen atoms that are double-bonded to other atoms. Thus, if we have a choice
between putting a hydrogen atom on an oxygen atom connected by a single
bond to another atom or putting it on one connected by a double bond to another
atom, we choose the former.
EXAMPLE 5.19
HCO
3
,
Draw all resonance structures for
in which the hydrogen atom is
bonded to a single-bonded oxygen atom.
