Page 15 - Mechanism and Theory in Organic Chemistry

Example 1. NO,
STEP 1 17 valence electrons, 0 charge = 17 electrons
.. . ..
STEP 2 O=N-0 . . : . ..
(Formation of another bond, ~=N=O, would give nitrogen valence-
shell occupancy 9.)
STEP 3 Formal charge :
Left 0 Ownership 6 0 charge
Right 0 Ownership 7 - 1 charge
N Ownership 4 + 1 charge

Correct Lewis Structure:
.. . + .. -
O=N-0 . . :
Example 2. - Ion
STEP 1 22 valence electrons, + 2 electrons for charge, = 24 electrons.

(More bonds to C would exceed its valence-shell limit.)
STEP 3 Formal charge:
.
-
: 0- Ownership 7 - 1 charge
. .
. .
: 0- Ownership 7 - 1 charge
. .
=O Ownership 6 0 charge
. .
C Ownership 4 0 charge
Correct Lewis Structure:

Resonance
The Lewis structure notation is useful because it conveys the essential qualitative
information about properties of chemical compounds. The main features of the
chemical properties of the groups that make up organic molecules,
H
I I \ .. I ..
H-C-H -C-H 0 -C-0-H
I I / I
H

and so forth, are to a first approximation constant from molecule to molecule,
and one can therefore tell immediately from the Lewis structure of a substance
that one has never encountered before roughly what the chemical properties will
be.