Question

Predict the bond angles for these 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

The bond angles in BeCl2, BCl3, CCl4, CH3Cl, ClHgHgCl, SnCl2, H2O2, and SnH4 are 180, 120, 109.5, 109.5, 180, <120 (close to 109.5), <109.5, and 109.5 degrees respectively.

Step-by-step solution

Identify the geometry of BeCl2

Beryllium in BeCl2 has two bonded atoms and no lone pairs, which corresponds to a linear geometry. The bond angle in a linear molecule is 180 degrees.

Predict the bond angle in BCl3

Boron in BCl3 has three bonded atoms and no lone pairs, which corresponds to a trigonal planar arrangement. The bond angle in a trigonal planar molecule is 120 degrees.

Assess the geometry of CCl4

Carbon in CCl4 has four bonded atoms and no lone pairs, corresponding to a tetrahedral geometry. The bond angle in a tetrahedral molecule is 109.5 degrees.

Determine the bond angle in CH3Cl

Like Carbon in CCl4, Carbon in CH3Cl also has a tetrahedral geometry. Thus, the bond angle is also 109.5 degrees.

Understand the geometry of ClHgHgCl

Each Mercury in ClHgHgCl is connected to two atoms (one Hg and one Cl). This corresponds to a linear geometry. Thus, the bond angle is 180 degrees.

Discover the bond angle in SnCl2

Tin in SnCl2 has two bonded atoms and one lone pair, corresponding to a bent or V-shaped geometry. The expected bond angle is less than 120 degrees, due to the greater repulsion by the lone pair, but typically close to 109.5 degrees.

Analyze the geometry of H2O2

In H2O2, each Oxygen atom has two bonds (one to Hydrogen and one to another Oxygen) and two lone pairs, corresponding to a bent or V-shaped geometry. Thus, the bond angle is less than 109.5 degrees.

Conclude with SnH4

Tin in SnH4 has four bonded atoms and no lone pairs, so it has a tetrahedral geometry. Thus, the bond angle is 109.5 degrees.

Key concepts

Bond Angles

Bond angles are the angles formed between three atoms bonded together. They are crucial for understanding the shape and properties of molecules. For example, in a molecule like water (H₂O), the bond angle between the hydrogen atoms is around 104.5 degrees.
The bond angles depend on the molecular geometry and the presence of lone pairs of electrons.

• In linear geometries, such as BeCl₂, the bond angle is 180 degrees.
• In a tetrahedral geometry like CCl₄, the bond angle is 109.5 degrees.
• A bent or V-shaped geometry, seen in SnCl₂, has bond angles slightly less than 109.5 degrees due to lone pair repulsion.

Always remember that bond angles are affected by factors such as atomic size and lone pair interactions.

VSEPR Theory

The Valence Shell Electron Pair Repulsion (VSEPR) theory helps predict the shape of a molecule. It states that electron pairs around a central atom will arrange themselves to minimize repulsion. Hence, different shapes arise depending on the number of bonding and non-bonding electron pairs.
VSEPR theory provides a straightforward way to predict molecular geometry:

• Linear Geometry: Occurs when there are two regions of electron density, with the angle between them being 180 degrees.
• Tetrahedral Geometry: Occurs with four regions of electron density, resulting in bond angles of 109.5 degrees.
• Trigonal Planar: Happens with three electron regions, giving bond angles of 120 degrees.
• Bent or V-shaped: Results from lone pairs affecting the angle, often making it less than 120 or 109.5 degrees.

VSEPR theory is essential for understanding molecular shapes and predicting chemical behavior.

Linear Geometry

Linear geometry is a molecular shape where atoms are arranged in a straight line. This shape is typical when there are two areas of electron density around the central atom, forcing a 180-degree bond angle.
Some key features of linear geometry include:

• Bond angle is precisely 180 degrees.
• Examples include BeCl₂ and ClHgHgCl.
• There are usually no lone pairs on the central atom in linear molecules.

Linear geometry is typically seen in diatomic molecules and some triatomic molecules like carbon dioxide.

Tetrahedral Geometry

Tetrahedral geometry is a common molecular shape, where a central atom is connected to four other atoms. The atoms are spaced equally around the central atom, resulting in bond angles of 109.5 degrees. This distribution minimizes repulsion between electrons.
Important aspects of tetrahedral geometry are:

• The bond angle is a critical 109.5 degrees, as seen in methane (CH₄), which helps balance the repulsive forces.
• It is common in molecules like CCl₄ and SnH₄.
• There are no lone pairs on the central atom in a perfect tetrahedral structure.

Tetrahedral geometry is fundamental in chemistry, as it provides stability and symmetry in molecular structures.