Question

What is the hybridization of the carbon atom in phosgene, \(\mathrm{Cl}_{2} \mathrm{CO}\) ? Give a complete description of the \(\sigma\) and \(\pi\) bonding in this molecule.

Short answer

The carbon atom in phosgene is \(sp^2\) hybridized with three \(\sigma\) bonds and one \(\pi\) bond.

Step-by-step solution

Determine the Central Atom

In phosgene, \(\text{Cl}_2\text{CO}\), the central atom is the carbon atom. This is because carbon typically forms four bonds and acts as the central atom when it is present in the compound.

Calculate the Steric Number

The steric number is the sum of the number of atoms bonded to the central atom and the number of lone pairs on the central atom. In phosgene, carbon is bonded to two chlorine atoms and one oxygen atom, with no lone pairs on carbon. Therefore, the steric number is 3.

Determine the Hybridization

The hybridization of the central atom can be determined from its steric number. A steric number of 3 indicates \(sp^2\) hybridization. Thus, the carbon atom in phosgene is \(sp^2\) hybridized.

Describe the Sigma (\(\sigma\)) Bonding

In an \(sp^2\) hybridized carbon, there are three \(sp^2\) orbitals available for sigma bonding. In phosgene, each \(sp^2\) orbital on carbon forms a sigma bond: one with the oxygen atom and one with each chlorine atom. Thus, there are a total of three \(\sigma\) bonds in phosgene.

Describe the Pi (\(\pi\)) Bonding

The remaining unhybridized \(p\) orbital on the \(sp^2\) hybridized carbon atom can overlap with a \(p\) orbital on the oxygen atom to form a \(\pi\) bond, resulting in a double bond between carbon and oxygen. Thus, there is one \(\pi\) bond involving the carbon atom in phosgene.

Key concepts

Phosgene

Phosgene, represented by the chemical formula \( ext{Cl}_2 ext{CO}\), is a toxic compound that is colorless and has a musty odor. It was historically used during World War I as a chemical weapon. In chemical bonding, phosgene is an important example of a molecule with both single and double bonds.
Its structure consists of a carbon (C) atom bonded to two chlorine (Cl) atoms and one oxygen (O) atom. The carbon atom serves as the central atom in this molecule. When we're examining the bonds, each type of atom plays a specific role:

• The central carbon atom can form a total of four bonds.
• Two single bonds are formed with each chlorine atom.
• A carbon-oxygen double bond is established, contributing significance to phosgene’s reactivity and properties.

Understanding the structure and bonding in phosgene is crucial for grasping its hybridization characteristics and the specific wave features of sigma and pi bonds.

Sigma bonding

Sigma (\(\sigma\)) bonding refers to the head-on overlap of orbitals, which creates the strongest type of covalent bond due to its direct overlap along the bond axis. In the case of phosgene, the carbon atom is \(sp^2\) hybridized. This means it forms three \(sp^2\) hybrid orbitals.

• One \(sp^2\) hybrid orbital overlaps with an \(s\) orbital from the oxygen atom to form a \(\sigma\) bond.
• Each of the remaining \(sp^2\) orbitals forms a \(\sigma\) bond with the \(3p_z\) orbitals of the two chlorine atoms.

This results in a total of three \(\sigma\) bonds in phosgene. Because these bonds involve the overlap of hybrid orbitals with atomic orbitals, they are positioned in a trigonal planar arrangement around the carbon atom, which minimizes repulsion and stabilizes the molecule.

Pi bonding

Pi (\(\pi\)) bonding occurs through the side-by-side overlap of the unhybridized \(p\) orbitals, which happens above and below the bonding axis of the atoms. In phosgene, after forming three \(\sigma\) bonds using \(sp^2\) orbitals, the carbon atom retains one unhybridized \(p\) orbital.
This \(p\) orbital on carbon can overlap with a \(p\) orbital on the oxygen atom, facilitating the formation of a \(\pi\) bond as part of the carbon-oxygen double bond.

• This \(\pi\) bond is what allows the molecule to exhibit characteristics associated with double bonding, such as restricted rotation and a shorter bond length compared to a single bond.

The pi bond, therefore, plays a crucial role in the chemical behavior and stability of phosgene, making it a molecule rich in chemical interactions.

Chemical bonds

Chemical bonds are the connections between atoms in a molecule that define its structure and influence its properties. In phosgene, both \(\sigma\) and \(\pi\) bonds are present, each contributing differently to the molecule's characteristics.

• \(\sigma\) bonds offer molecular stability and strength by allowing tight orbital overlap along the bond axis.
• \(\pi\) bonds add to the molecule’s reactivity by providing additional overlap avenues, which can alter bond angles and lengths.

The interplay between these types of bonds affects everything from physical properties to reactivity and environmental behavior. By understanding the nature of these bonds, chemists can predict how phosgene might behave in various scenarios, helping to anticipate its impact as well as how to mitigate any harmful effects it may have.