Understanding the Oxidation Number of CN: Detailed Insights and Applications

Introduction to the Cyanide Ion (CN-)

The cyanide ion, denoted as CN-, is a monovalent anion that consists of a carbon atom (C) single-bonded to a nitrogen atom (N). It plays a significant role in various chemical reactions and environments due to its unique electronic and structural properties. The determination of the oxidation number of each atom in the cyanide ion is crucial for understanding its behavior and interactions.

Diagonal Determination of Oxidation States

The normal oxidation states of the constituent atoms in a molecule or ion can be used to find their specific oxidation states. For CN-, the oxidation state of nitrogen (N) is typically -3, and carbon (C) is 4 when bonded to less electronegative elements. However, in the cyanide ion, nitrogen is more electronegative than carbon, leading to a different arrangement.

A Mathematical Approach

Let's denote the oxidation number of carbon as x. The overall charge of the cyanide ion is -1. According to the sum of oxidation states principle:

x - 3 -1

Solving for x gives us:

x - 3 -1
cancel -3 on both sides: x -1 3
x 2

Hence, the oxidation number of carbon (C) in CN- is 2, and the oxidation number of nitrogen (N) is -3. This can also be verified with the idea that nitrogen gets the six electrons of the triple bond due to its higher electronegativity, giving it a formal -3 charge.

Application in Complex Compounds

The understanding of oxidation states in CN- is particularly relevant when dealing with more complex compounds where the ion acts as a ligand. For instance, in the coordination compound X4[Fe(CN)6], where X is any alkali metal, the oxidation states can be determined as follows:

The oxidation state of the cyanide ion (CN) is -1. The oxidation state of iron (Fe) is 2. The oxidation state of the alkali metal (X) is 1. The weighted sum of oxidation numbers equals the overall charge of the ion: 4( 1) 1( 2) 6(-1) 4 2 - 6 0

This confirms that the overall charge on the ion is neutral, as expected in a stable complex.

Additional Nuances and Context

The cyanide ion CN- is also observed in its gaseous form, hydrogen cyanide (HCN), where it dissociates into a hydrogen ion (H ) and a cyanide ion (CN-). In this form, the cyanide ion retains its -1 charge.

It is important to understand that the oxidation states are context-specific and depend on the elements involved and their electronic configurations. In the case of CN-, the strong interaction between carbon and nitrogen, with nitrogen being more electronegative, defines their formal charges.