Question Video: Deducing the Oxidation Number of an Oxygen Atom in Molecular Oxygen | Nagwa Question Video: Deducing the Oxidation Number of an Oxygen Atom in Molecular Oxygen | Nagwa

Question Video: Deducing the Oxidation Number of an Oxygen Atom in Molecular Oxygen Chemistry • Second Year of Secondary School

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What is the oxidation number of oxygen in O₂?

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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.

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