Problem 29 - A Complete Resource Book in Chemistry for JEE Main

Question

The \(\mathrm{H}-\mathrm{O}-\mathrm{O}\) bond angle in \(\mathrm{H}_{2} \mathrm{O}_{2}\) is (a) \(97^{\circ}\) (b) \(106^{\circ}\) (c) \(104.5^{\circ}\) (d) \(109.28^{\circ}\)

Step-by-Step Solution

Answer

The H-O-O bond angle in H2O2 is (a) 97°.

Step 1: Understanding the Structure of Hydrogen Peroxide

To find the bond angle, first recognize hydrogen peroxide's molecular structure, which consists of two hydrogen atoms bonded to an oxygen atom each, with an 'O-O' single bond connecting the two oxygen atoms. The geometry around the oxygens determines the bond angle.

Step 2: Considering the Molecular Geometry

Each oxygen atom in hydrogen peroxide is sp3 hybridized, leading to a tetrahedral arrangement of bonds and lone pairs around each oxygen atom. However, the actual observed shape is skewed open due to steric and electronic factors.

Step 3: Analyzing Bond Angles in Hydroperoxides

In molecules like H2O2, the presence of lone pairs causes the bonded angle to decrease from the tetrahedral angle (109.5°). The lone pairs repel more strongly than bonding pairs, thus reducing the bond angles.

Step 4: Identifying the Answer from Options

Given the options, we know the bond angle in hydrogen peroxide is slightly less than the tetrahedral angle due to each oxygen atom's lone pairs. Commonly, the observed hydrogen peroxide H-O-O bond angle is approximately 97°.

Key Concepts

Hydrogen Peroxide Structure

Hydrogen peroxide (H₂O₂) is a simple compound that consists of two hydrogen atoms and two oxygen atoms. Each hydrogen atom is bonded to one of the oxygen atoms, forming a structure with an 'O-O' single bond at its center. This arrangement gives hydrogen peroxide a unique structure that can best be visualized as two bent H-O-O molecular units connected together by the O-O bond. The presence of this single oxygen-oxygen bond is atypical for most simple molecules and significantly affects the overall geometry and chemistry of the compound.

In order to comprehend its structure, it is helpful to recognize two key aspects. First, each hydrogen is only involved in one bonding interaction, which is with its corresponding oxygen. Second, the central 'O-O' bond introduces a degree of flexibility; unlike double or triple bonds, single bonds allow for rotations, affecting the spatial arrangement of the atoms involved.

Molecular Geometry

The molecular geometry of hydrogen peroxide can be somewhat confusing due to those lone pairs on the oxygen atoms. Despite the fact that an oxygen center that is sp³ hybridized would suggest a tetrahedral geometry, hydrogen peroxide's geometry is far from the perfect tetrahedron.

In reality, the molecule appears more tetrahedral but distorted. Each oxygen atom forms two bonds with hydrogen atoms and holds two lone pairs. This situation results in a geometry where the lone pairs strongly influence the shape by repelling each other and the bonded pairs.

• The strong repulsion from lone pairs makes the bond angle between the hydrogen-oxygen-oxygen ( 37;O-O) slightly smaller.
• This leads to the bent molecular shape, where the ideal 109.5° tetrahedral angle shrinks significantly, following the fundamental principles of VSEPR (Valence Shell Electron Pair Repulsion) theory.

Ultimately, this distorted version still honors the sp³ hybridization, though it manifests as a readable characteristic of the molecular electronic environment rather than an unperturbed structural model.

Hybridization

Hybridization is a concept that helps to explain the arrangement of electrons in an atom, which then determines molecule's shape and angle, as seen in hydrogen peroxide. Here, each oxygen atom in H₂O₂ undergoes sp³ hybridization. This means that one s orbital and three p orbitals mix to form four equivalent hybrid orbitals.

One of the crucial implications of hybridization is its impact on bond angles. With sp³ hybridization, one would expect a nearly perfect tetrahedral shape with 109.5° angles. However, due to lone pair-bond pair repulsions being stronger than bond-bond repulsions, these angles are distorted.

• In hydrogen peroxide, the greater space taken up by lone pairs compresses the bond angle.
• Actual bond angles end up being notably smaller than the predicted tetrahedral geometry.

The concept of hybridization provides an intuitive framework to help us understand how orbitals come together to create the electron geometry that impacts hydrogen peroxide's actual molecular structure.