Question

Predict the bond angles for the following molecules: (a) \(\mathrm{BeCl}_{2}\), (b) \(\mathrm{BCl}_{3}\) (c) \(\mathrm{CCl}_{4}\) (d) \(\mathrm{CH}_{3} \mathrm{Cl}\) (e) \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\) (arrangement of atoms: \(\mathrm{ClHgHgCl}\) ), (f) \(\mathrm{SnCl}_{2}\), (g) \(\mathrm{H}_{2} \mathrm{O}_{2},\) (h) \(\mathrm{SnH}_{4}\).

Short answer

Bond angles: BeCl2: 180°, BCl3: 120°, CCl4: 109.5°, CH3Cl: 109.5°, Hg2Cl2: 180°, SnCl2: 95°-100°, H2O2: 94.8°, SnH4: 109.5°.

Step-by-step solution

Analyze Molecular Geometry for BeCl2

Beryllium chloride (\(\mathrm{BeCl}_{2}\)) forms a linear geometry due to the central beryllium atom forming only two bonds and having no lone pairs. Thus, the bond angle is \(180^\circ\).

Determine Geometry for BCl3

Boron trichloride (\(\mathrm{BCl}_{3}\)) forms a trigonal planar structure with boron at the center. The absence of lone pairs on boron leads to equal bonding angles of \(120^\circ\).

Evaluate CCl4 Geometry

Carbon tetrachloride (\(\mathrm{CCl}_{4}\)) encompasses a tetrahedral geometry around the carbon atom with bond angles of approximately \(109.5^\circ\).

Assess Geometry for CH3Cl

Methyl chloride (\(\mathrm{CH}_{3}\mathrm{Cl}\)) adopts a tetrahedral shape around the carbon, with bond angles close to \(109.5^\circ\), owing to the carbon atom bonding to four other atoms or groups.

Geometry for Hg2Cl2

Mercury(I) chloride (\(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\)) has a linear arrangement due to two Hg atoms sharing a pair of electrons, leading to a \(180^\circ\) bond angle.

Determine Geometry for SnCl2

Tin(II) chloride (\(\mathrm{SnCl}_{2}\)) features bent geometry due to lone pair repulsion on tin, resulting in bond angles less than \(120^\circ\). Approximate bond angle is \(95^\circ - 100^\circ\).

Analyze Bond Angle in H2O2

Hydrogen peroxide (\(\mathrm{H}_{2}\mathrm{O}_{2}\)) forms a skewed structure with the O-O-H bond angle estimated to be around \(94.8^\circ\) due to repulsion involving the unpaired electron clouds.

Geometry for SnH4

Tin(IV) hydride (\(\mathrm{SnH}_{4}\)) forms a regular tetrahedral structure, with bond angles about \(109.5^\circ\) due to the shape accommodating four hydrogens around tin.

Key concepts

Bond Angles

Bond angles are the angles between two covalent bonds that share a common atom, typically the central atom in a molecule. The size of bond angles plays a crucial role in determining molecular geometry and influences the molecule's physical and chemical properties. Generally, the bond angle depends on:

• The number of bonds formed by the central atom.
• The presence of lone pairs of electrons.
• The repulsion forces according to VSEPR (Valence Shell Electron Pair Repulsion) theory.

In a linear molecule like \(\mathrm{BeCl}_{2}\), with two bonded atoms and no lone pairs, the bond angle measures \(180^\circ\). In contrast, molecules like \(\mathrm{CCl}_4\) have tetrahedral geometry giving a bond angle of approximately \(109.5^\circ\). This illustrates how geometry plays a part in defining bond angles, contributing to the molecule's overall shape.

Linear Geometry

Linear geometry refers to a molecular shape where the atoms are aligned in a straight line. Typically, this geometry results when the central atom forms only two bonds with no lone pair electrons exerting extra repulsive forces. In these molecules, like \(\mathrm{BeCl}_{2}\) and \(\mathrm{Hg}_{2}\mathrm{Cl}_{2}\), the bond angle is \(180^\circ\).Linear geometry is prevalent in various diatomic molecules due to the absence of any central atom. However, for triatomic molecules like \(\mathrm{BeCl}_{2}\), the central atom's valence electrons are occupied in bond formation, ensuring the structure remains linear. This streamlined shape minimizes electron pair repulsions, facilitating a stable and predictable geometrical structure. Understanding linear geometry is essential to predicting and explaining the molecular angles and overall configuration.

Trigonal Planar

Trigonal planar geometry occurs when a central atom is bonded to three other atoms or groups and has no lone pairs. This shape allows molecules to have bond angles of \(120^\circ\), distributing the bonding pairs equally around the central atom.A classic example is \(\mathrm{BCl}_3\), with boron as the central atom and three chlorine atoms arranged symmetrically. The lack of lone pairs leads to equal attraction between the bonding electrons, creating a plane and ensuring the bond angles remain at \(120^\circ\). Trigonal planar geometry is significant in understanding how lone pair absence simplifies the molecular shape and stabilizes bond angles, influencing reactivity and molecular polarity.

Tetrahedral Shape

The tetrahedral shape is a common molecular geometry where a central atom is bonded to four other atoms, with bond angles close to \(109.5^\circ\). This shape occurs because of symmetrical distribution around the central atom, balancing repulsion forces to achieve maximal stability. Examples include \(\mathrm{CCl}_4\) and \(\mathrm{CH}_3\mathrm{Cl}\), where carbon at the center is bonded to four groups. The tetrahedral arrangement accommodates four pairs of shared electrons, which space out evenly in three-dimensional space, thereby minimizing electron pair repulsion. Understanding tetrahedral geometry aids in predicting physical properties such as boiling and melting points, as these structures impact intermolecular forces and, ultimately, the molecule's physical state at various temperatures.