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When describing the ground-states of neutral molecules, it is desirable that the
formal charges be small in magnitude, i.e. less than unity. This requirement should
be particularly appropriate when atoms A and B have fairly similar neutral atom
electronegativities.
In Chapter 11, we have found that fluorine atoms could stabilize appreciably
the Pauling “3-electron bond(s)” of NO, O 2 , SO and S 2 , and that “increasedvalence” structures (9) and (11) are suitable valence-bond structures for FNO and
F 2 O 2 . Therefore, if we write down the standard Lewis structures (8) and (10), the
fluorine atom(s) must induce appreciable delocalization of oxygen lone-pair
electron(s) into the N-O and O-O bonding orbitals. We have indicated these delocalizations in structures (8) and (10). On the other hand, hydrogen atoms do not
generate appreciable stabilization of Pauling “3-electron bonds” (Sections 11-3
and 11-4) of 4-electron 3-centre bonding units in neutral molecules, and similar
oxygen delocalizations for HNO and H 2 O 2 must occur only to a very small extent.
We have found that the standard Lewis structures (12) and (13) alone are adequate
simple representations of the electronic structures of these molecules.
Figure 12-1: Generation of “increased-valence” structures from standard Lewis structures by
delocalizing lone-pair electrons into vacant bonding orbitals.
Chapter 12
Constructed from Lewis Structures
“Increased-Valence” Structures
When describing the ground-states of neutral molecules, it is desirable that the
formal charges be small in magnitude, i.e. less than unity. This requirement should
be particularly appropriate when atoms A and B have fairly similar neutral atom
electronegativities.
In Chapter 11, we have found that fluorine atoms could stabilize appreciably
the Pauling “3-electron bond(s)” of NO, O 2 , SO and S 2 , and that “increasedvalence” structures (9) and (11) are suitable valence-bond structures for FNO and
F 2 O 2 . Therefore, if we write down the standard Lewis structures (8) and (10), the
fluorine atom(s) must induce appreciable delocalization of oxygen lone-pair
electron(s) into the N-O and O-O bonding orbitals. We have indicated these delocalizations in structures (8) and (10). On the other hand, hydrogen atoms do not
generate appreciable stabilization of Pauling “3-electron bonds” (Sections 11-3
and 11-4) of 4-electron 3-centre bonding units in neutral molecules, and similar
oxygen delocalizations for HNO and H 2 O 2 must occur only to a very small extent.
We have found that the standard Lewis structures (12) and (13) alone are adequate
simple representations of the electronic structures of these molecules.
Figure 12-1: Generation of “increased-valence” structures from standard Lewis structures by
delocalizing lone-pair electrons into vacant bonding orbitals.
Chapter 12
Constructed from Lewis Structures
“Increased-Valence” Structures