What is the Oxidation Number of Cyanide (CN)?

The Cyanide ion is a polyatomic ion with the chemical formula $CN^-$. Because it has a single negative charge, the overall oxidation number of the entire CN group is -1.

If a question asks for the specific oxidation states of the Carbon (C) and Nitrogen (N) atoms inside the cyanide ion, we must look at their electronegativity.

• Nitrogen is more electronegative than Carbon.
• In the $C \equiv N$ triple bond, Nitrogen pulls the shared electrons towards itself.
• Therefore, Nitrogen (N) has an oxidation state of -3.
• To make the total charge -1, Carbon must balance it out. Let Carbon's oxidation number be $x$. $x + (-3) = -1$ $x = +2$
• Therefore, Carbon (C) has an oxidation state of +2 in the cyanide ion.

In complex coordination compounds (like Potassium ferrocyanide, $K_4[Fe(CN)_6]$), the CN group acts as a strong-field ligand. When calculating the oxidation state of the central metal atom (like Iron), you will always use -1 as the oxidation number for each CN ligand.