Question

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

Short answer

The carbon in phosgene is \(\mathrm{sp^2}\) hybridized, forming \(\sigma\) bonds with both chlorines and oxygen, and a \(\pi\) bond with oxygen.

Step-by-step solution

Determine Carbon Atom's Hybridization

To find the hybridization of the carbon atom in phosgene (ClyC=O), we examine how many attachment points the carbon atom has. There are two chlorine atoms and one oxygen atom connected to carbon. Count both single bonds and double bonds equally as one attachment each. Therefore, the carbon in phosgene has three total points of attachment, indicating \(\mathrm{sp^2}\) hybridization.

Description of \(\sigma\) Bonding

\(\sigma\) bonds are formed by the overlap of hybrid orbitals. In phosgene, the carbon atom is \(\mathrm{sp^2}\) hybridized, so it has three \(\mathrm{sp^2}\) orbitals available. These orbitals overlap with one 3p orbital from each chlorine atom and an \(\mathrm{sp^2}\) or \(\text{lone pair }2p\) orbital from the oxygen. Therefore, all three \(\mathrm{sp^2}\) hybrid orbitals from carbon form \(\sigma\) bonds: two with the chlorine atoms and one with the oxygen atom.

Description of \(\pi\) Bonding

\(\pi\) bonds are formed by the lateral overlap of unhybridized p orbitals. In phosgene, the carbon-oxygen double bond consists of one \(\sigma\) bond and one \(\pi\) bond. The \(\pi\) bond forms by the side-by-side overlap of a p orbital reserved on the carbon and a compatible p orbital on the oxygen atom.

Electron Geometry Verification

Verify \(\mathrm{sp^2}\) hybridization by examining the molecular geometry of phosgene. The carbon is central, bound to two chlorines and one oxygen, making the electron geometry trigonal planar when considering the three attachment points. This geometry is consistent with \(\mathrm{sp^2}\) hybridization.

Key concepts

Sigma and Pi Bonding

Understanding sigma (\( \sigma \)) and pi (\( \pi \)) bonding is crucial in hybridization. Sigma bonds are the primary bonds formed by direct overlap of orbitals. In phosgene, the carbon atom is \( \mathrm{sp^2} \) hybridized, which means it holds three \( \mathrm{sp^2} \) hybrid orbitals. These orbitals engage in sigma bonding with two chlorine atoms and one oxygen atom.

• Each \( \mathrm{C-Cl} \) bond is a sigma bond formed by the overlap of a carbon \( \mathrm{sp^2} \) orbital and a chlorine 3p orbital.
• The \( \mathrm{C=O} \) double bond consists of one sigma bond between a carbon \( \mathrm{sp^2} \) orbital and an oxygen \( \mathrm{sp^2} \) or lone pair 2p orbital.
• For the pi bond, the unhybridized p orbital of carbon overlaps laterally with a p orbital of oxygen.

Sigma bonds are stronger than pi bonds, as they involve head-on overlapping. Pi bonds, however, provide extra connection strength by adding a sideways overlap. Both bonding types work together to stabilize molecules.

sp2 Hybridization

Hybridization refers to the mixing of atomic orbitals to create new hybrid orbitals. In phosgene, carbon's \( \mathrm{sp^2} \) hybridization results from mixing one 2s and two 2p orbitals, forming three equivalent \( \mathrm{sp^2} \) orbitals. These are arranged around the carbon for optimal bonding, resulting in a trigonal planar formation typical of this hybridization type.

• The trigonal planar arrangement is due to the equal energy level and geometric spacing of these hybrid orbitals.
• This hybridization allows carbon to have one remaining unhybridized p orbital, available for \( \pi \) bonding with oxygen.
• Each \( \mathrm{sp^2} \) hybrid orbital forms a sigma bond with either chlorine or oxygen.

The concept of \( \mathrm{sp^2} \) hybridization helps explain the carbon's ability to form versatile compounds with different atoms.

Trigonal Planar Geometry

Trigonal planar geometry is a structural arrangement where a central atom, like carbon in phosgene, is connected to three atoms positioned at the corners of an equilateral triangle. These atoms, including two chlorine and one oxygen, create a 120-degree angle between each bond.

• Such a structure is indicative of \( \mathrm{sp^2} \) hybridization.
• Each peripheral atom in this setup lies in the same plane as the central atom.
• The consistent angles and planar arrangement are essential for molecular stability and reactivity.

Trigonal planar geometry ensures there is minimal repulsion between electrons in the bonds by maximizing their separation, which is crucial for understanding molecular shapes and electron distribution.

Electron Geometry Verification

Verifying electron geometry involves matching predicted and actual shapes of molecules. For phosgene, this verification confirms \( \mathrm{sp^2} \) hybridization through its trigonal planar electron arrangement.

• Carbon in phosgene maintains three points of attachment—two chlorines and one oxygen, consistent with \( \mathrm{sp^2} \) hybridization.
• The overall shape should correspond to the trigonal planar model, validating the calculated hybrid state.
• Observing bond angles also reinforces symmetry, further confirming the predicted geometry.

Accurate electron geometry verification is vital because it connects theoretical understanding with observable chemical behavior, ensuring correct predictions about molecular interactions and properties.