Question

Using the VSEPR theory, predict the molecular structure of each of the following molecules. a. \(\mathrm{CCl}_{4}\) b. \(\mathrm{H}_{2} \mathrm{S}\) c. \(\mathrm{Gel}_{4}\)

Short answer

The molecular structures of the given molecules according to VSEPR theory are: a. \(CCl_4\) - Tetrahedral b. \(H_2S\) - Bent or angular c. \(GeI_4\) - Tetrahedral

Step-by-step solution

Molecule a: CCl4

For CCl4, the central atom is Carbon (C), as it has the ability to form up to 4 bonds. Each surrounding Chlorine (Cl) atom contributes one bond, resulting in a total of 4 bond pairs and no lone pairs. According to VSEPR theory, a molecule with 4 bond pairs and no lone pairs on the central atom will have a tetrahedral geometry.

Molecule b: H2S

For H2S, the central atom is Sulfur (S), as Hydrogen (H) can only form one bond. Each surrounding H atom contributes one bond, resulting in a total of 2 bond pairs. Sulfur has 6 valence electrons, so there are also 2 lone pairs on the central atom. According to VSEPR theory, a molecule with 2 bond pairs and 2 lone pairs on the central atom will have a bent or angular geometry.

Molecule c: GeI4

For GeI4, the central atom is Germanium (Ge), as Iodine (I) usually forms a single bond. Each surrounding Iodine (I) atom contributes one bond, resulting in a total of 4 bond pairs and no lone pairs. According to VSEPR theory, a molecule with 4 bond pairs and no lone pairs on the central atom will have a tetrahedral geometry. So, the molecular structures of the given molecules according to VSEPR theory are: a. CCl4 - Tetrahedral b. H2S - Bent or angular c. GeI4 - Tetrahedral

Key concepts

Molecular Geometry

Molecular geometry describes the three-dimensional shape or arrangement of atoms in a molecule. This concept is crucial for understanding properties such as polarity, reactivity, and color. The VSEPR (Valence Shell Electron Pair Repulsion) theory is often used to predict molecular geometry. It posits that electron pairs around a central atom will organize themselves as far apart as possible to minimize repulsions. By knowing the number of bond pairs and lone pairs, one can predict the molecular shape.

• Non-bonding electrons influence the shape more significantly as they occupy more space.
• Geometry affects physical and chemical properties, including boiling and melting points.

Bond Pairs and Lone Pairs

Bond pairs are shared pairs of electrons that form bonds between atoms, while lone pairs are unshared electrons residing on the central atom. In terms of molecular shapes, the number and type of these pairs around the central atom dictate the molecular geometry.
VSEPR theory classifies molecular shapes based on these electron pairs:

• Bond pairs attract each other, forming bonds, whereas lone pairs repel, often altering angles in molecule structures.
• Lone pairs exert more repulsion than bond pairs, which can lead to distortions from expected geometrical shapes.

Tetrahedral Geometry

Tetrahedral geometry is a common molecular shape where one atom is positioned at the center with four other atoms at each corner of a tetrahedron. This results from having four bond pairs and no lone pairs on the central atom.
Examples include molecules like CCl\(_4\) and GeI\(_4\). In these molecules:

• The bond angle is approximately 109.5 degrees.
• This geometry is symmetrical, often resulting in non-polarity when all external atoms are identical.

Tetrahedral geometry allows for precise predictions of molecule behavior, especially in reactions.

Bent Molecular Shape

Bent molecular shape arises when a central atom has two bond pairs and one or more lone pairs. In molecules like H\(_2\)S, the presence of lone pairs on the central atom (Sulfur) causes a bent shape, deviating from a linear configuration.
Characteristics of bent shape include:

• An angle generally less than 120 degrees, often around 104.5 degrees for water-like structures.
• The presence of lone pairs pushes bond pairs closer, creating a distinct angle.

Understanding this shape is vital for grasping how molecular interactions occur, as it influences dipole moments and chemical reactivity.