Author replies to Woolf
A. A. Woolf takes exception to my note on
balancing redox equations (J. Chem. Educ.
1996, 73, 507), remarking that oxidation numbers do have a "chemical
reality" in the CN- ion, for example. As Woolf mentions,
Gaussian orbital and perturbation calculations do show that
the N end of the ion is the more negative, but hardly by
a full electronic charge. My comment was that further information than would be available to a freshman
learning to balance equations would be needed to lead to
a preference in oxidation numbers. The beginning
student has seen N in the -3 and +3 oxidation states, and
carbon in the +2 and -4, but ordinarily would not have
met the concepts of either Lewis structures or
electronegativity so early in the course.
I consider it important that oxidation number
not be confused with charge; only the latter has physical
reality. (Surely the Mn atom in
MnO4- does not have a charge of +7; Coulomb's law would certainly not
permit such charge separation.) Students would get even
more confused later in the course when they see
formal charges if they were to consider them to be real as well.
Woolf rejects my use of nonintegral oxidation
numbers yet uses mean oxidation numbers, which are
nonintegral. I fail to see a difference.
I do mention using oxidation numbers as tools,
irrespective of whether they make "chemical sense" or
not. Similarly, almost everyone speaks of electrons in
orbitals, although, strictly, the orbital concept fails for
more than one electron system. Later in the course, when
the sophistication of the student has increased, we can
talk about models versus reality.
By the way, I use the ion-electron/half-reaction method when I teach balancing redox equations. I consider it closer to reality.
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