Video Transcript
What is the oxidation number of
oxygen in O2?
In this question, we need to
determine the oxidation number of oxygen in diatomic oxygen molecules. Let’s first look at the structure
and bonding of diatomic oxygen and then explain the term oxidation number.
Diatomic oxygen, O2, has a double
bond between its two oxygen atoms. The diagram shows the two pairs of
electrons in the double bond. Each oxygen atom has the same
electronegativity or ability to draw or pull a bonding pair of electrons towards
itself. We assign an electronegativity
number according to the relative electronegativity of an atom.
Oxygen atoms are assigned an
electronegativity number of 3.44. Since both atoms have the same
electronegativity number, we know that neither oxygen atom can withdraw or pull a
disproportionately large amount of electron density from the oxygen–oxygen double
bond.
Now let’s consider oxidation
number, sometimes referred to as oxidation state. Oxidation numbers are values that
quantify the degree of oxidation of an atom in terms of counting electrons. Oxidation numbers can be negative,
zero, or positive. We give an atom in a compound a
negative oxidation number when it has been reduced. We give an atom an oxidation number
of zero when it is neither oxidized nor reduced, but in its elemental state. And we assign a positive oxidation
number to an atom in a compound when it has been oxidized.
We should appreciate that oxygen
atoms are neither oxidized nor reduced when they bond to form molecular oxygen. They are in their elemental
state. They have the same
electronegativity number and share the bonding electrons equally. And thus, we can say that atoms in
their elemental state, even when bonded to an identical atom, are neither reduced
nor oxidized and so have a zero oxidation number.
So, what is the oxidation number of
oxygen in O2? The answer is zero.
