Question

When a methyl radical is formed from \(\mathrm{CH}_{3} \mathrm{Cl}\), select the correct statement: (1) Bond angle of \(109^{\circ} 28\) ' is retained (2) Number of sigma bonds is three (3) Carbon undergoes geometric change from tetrahedral to planar (4) Hybridization changes \(\mathrm{sp}^{3}\) to \(\mathrm{sp}^{2}\) (a) 2,3 and 4 (b) 1,3 and 4 (c) 2 and 4 (d) 3 and 4

Short answer

The correct answer is (a) 2, 3, and 4.

Step-by-step solution

Understand the Structure of \(\mathrm{CH}_{3} \mathrm{Cl}\)

The molecule \(\mathrm{CH}_{3} \mathrm{Cl}\) is composed of a carbon atom bonded to three hydrogen atoms and one chlorine atom. Carbon has a tetrahedral geometry due to its \(\mathrm{sp}^{3}\) hybridization, giving a bond angle of approximately \(109^{\circ} 28'\).

Formation of the Methyl Radical

The formation of a methyl radical occurs when one of the bonds, usually the \(\mathrm{C-Cl}\) bond, is broken, leaving the \(\mathrm{CH}_3\) group with an unpaired electron, making it a radical.

Analyze the Geometric Change

As the chlorine atom is removed, carbon changes from \(\mathrm{sp}^{3}\) hybridization to \(\mathrm{sp}^{2}\) hybridization. This leads to a planar structure for the methyl radical instead of the original tetrahedral structure.

Evaluate the Hybridization Change

With the unpaired electron, the hybridization of carbon changes from \(\mathrm{sp}^{3}\) (tetrahedral geometry) to \(\mathrm{sp}^{2}\) (trigonal planar geometry). Thus, the bond angle is no longer \(109^{\circ} 28'\) but closer to \(120^{\circ}\).

Verify the Number of Sigma Bonds

In the methyl radical \(\mathrm{CH}_3\), the carbon is still bonded to three hydrogen atoms via sigma bonds. Hence, the structure retains three sigma bonds even after the conversion.

Select the Correct Statements

Based on the steps analyzed: (2) Number of sigma bonds is three, (3) Carbon undergoes geometric change from tetrahedral to planar, and (4) Hybridization changes \(\mathrm{sp}^{3}\) to \(\mathrm{sp}^{2}\) are correct.

Key concepts

sp3 hybridization

In \( \text{sp}^3 \) hybridization, the central atom forms four equivalent hybrid orbitals. This arrangement facilitates the creation of four sigma bonds, which occurs in molecules like methane (\( \text{CH}_4 \)). Each \( \text{sp}^3 \) hybridized orbital results from the mixing of one s orbital and three p orbitals from the carbon atom.

Key aspects of \( \text{sp}^3 \) hybridization include:

• Formation of a tetrahedral shape with bond angles of approximately \( 109.5^\circ \).
• Four equivalent and symmetric bonds around the central atom.
• Characteristic of carbon atoms in saturated hydrocarbons.

When \( \text{CH}_3\text{Cl} \) undergoes a change to form a methyl radical, the \( \text{sp}^3 \) hybridized state shifts due to the breaking of the \( \text{C{-}Cl} \) bond. This conversion is significant because the carbon atom’s hybridization state affects the molecule’s geometry and electron configuration.

tetrahedral geometry

Tetrahedral geometry refers to the shape formed when a central atom is symmetrically surrounded by four atoms or groups. It is a prevalent shape for molecules with \( \text{sp}^3 \) hybridization because the hybrid orbitals are oriented as far apart as possible in three dimensions. This geometry helps minimize electron pair repulsion, according to VSEPR theory.

Features of tetrahedral geometry include:

• A central atom bonded to four peripheral atoms.
• Bond angles of about \( 109.5^\circ \), ensuring optimal spacing.
• Exemplified by simple molecules like methane, \( \text{CH}_4 \).

In the original structure of \( \text{CH}_3\text{Cl} \), the carbon atom exhibits tetrahedral geometry. However, the removal of the chlorine atom to form a methyl radical alters this arrangement. As a result, tetrahedral geometry becomes disrupted, leading to changes in the overall molecular shape.

planar structure

A planar structure emerges in molecules that adopt a \( \text{sp}^2 \) hybridization configuration. This arrangement consists of three hybrid orbitals formed by mixing one s and two p orbitals, resulting in a trigonal planar shape. Such a structure means that the atoms are organized in a flat plane.

Characteristics of a planar structure include:

• A carbon atom bonded to three atoms and one unbonded or lone electron.
• Bond angles that approach \( 120^\circ \).
• Molecules such as ethylene (\( \text{C}_2\text{H}_4 \)) exhibit planar geometry.

As the methyl radical \( \text{CH}_3 \) is formed from \( \text{CH}_3\text{Cl} \), the carbon atom transitions from a tetrahedral to a planar configuration. This shift is crucial as it impacts both the shape and reactivity of the molecule. The planar nature allows for greater overlap of p orbitals, influencing interaction with other molecules or radicals.