Question

The hybridizations of the carbon and nitrogen atoms in \(\mathrm{CN}^{-}\) are: A. \(s p^{3}\) and \(s p^{3},\) respectively. B. \(s p^{3}\) and \(s p,\) respectively. C. \(s p\) and \(s p^{3},\) respectively. D. \(s p\) and \(s p,\) respectively.

Short answer

D. \(sp\) and \(sp\).

Step-by-step solution

- Determine the structure of \(\text{CN}^{-}\)

The cyanide ion \(\text{CN}^{-}\) consists of a carbon atom triple-bonded to a nitrogen atom, with a negative charge on the nitrogen.

- Examine the hybridization of the carbon atom

In the \(\text{CN}^{-}\) ion, the carbon atom forms two sigma bonds and has no lone pairs, implying it uses two hybrid orbitals, which corresponds to \(sp\) hybridization.

- Examine the hybridization of the nitrogen atom

In the \(\text{CN}^{-}\) ion, the nitrogen atom forms one sigma bond and has one lone pair, implying it uses two hybrid orbitals, which also corresponds to \(sp\) hybridization.

- Confirm the hybridization types

Both carbon and nitrogen in the \(\text{CN}^{-}\) ion use \(sp\) hybrid orbitals.

- Select the correct option

Based on the hybridization of both atoms being \(sp\), the correct answer is D. \(sp\) and \(sp\), respectively.

Key concepts

sp hybridization

In chemistry, hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals. These hybrid orbitals are different in energy and shape than the original atomic orbitals. To understand the hybridization in the cyanide ion \(\text{CN}^{-}\), let's focus on sp hybridization. This type occurs when one s orbital and one p orbital from the same atom mix to form two equivalent sp hybrid orbitals. Each of these orbitals has 50% s character and 50% p character.
When we look at carbon in \(\text{CN}^{-}\), it forms two sigma bonds with nitrogen, resulting in two unhybridized p orbitals being available for forming a triple bond. Thus, carbon uses sp hybrid orbitals.
Similarly, nitrogen, in \(\text{CN}^{-}\), forms one sigma bond with carbon and holds one lone pair of electrons, leading to sp hybridization.

sigma bonds

Sigma (\(\text{σ}\)) bonds are a type of covalent bond and are the strongest kind of bond in molecules. They occur when two atomic orbitals overlap directly between the bonding atoms' nuclei. This direct overlap allows the shared electrons to be as close to the nuclei as possible, which increases the bond's strength.
In the \(\text{CN}^{-}\) ion, both carbon and nitrogen atoms form sigma bonds. Carbon forms two sigma bonds with nitrogen. These sigma bonds are part of the triple bond between carbon and nitrogen—one sigma bond and two pi bonds. The strong sigma bond ensures that the \(\text{CN}^{-}\) ion is held together tightly, contributing to its stability.

lone pairs

Lone pairs are pairs of valence electrons that are not involved in chemical bonding. They are located on a specific atom and influence the shape and reactivity of a molecule. In the cyanide ion (\(\text{CN}^{-}\)), nitrogen has one lone pair.
Let's delve into its role in \(\text{CN}^{-}\). Because nitrogen has a lone pair, it will repel other electron pairs around it, affecting the molecule's geometry. The presence of the lone pair also means that nitrogen must use one of its sp hybrid orbitals to accommodate these electrons. This results in both carbon and nitrogen having sp hybridization.
Lone pairs can also be reactive points in a molecule. For instance, the lone pair on nitrogen in \(\text{CN}^{-}\) can participate in the formation of additional bonds or interact with other molecules during chemical reactions.