Question

For each of the following molecules or ions, indicate the bond angle expected between the central atom and any two adjacent chlorine atoms. a. \(\mathrm{Cl}_{2} \mathrm{O}\) b. \(\mathrm{NCl}_{3}\) c. \(\mathrm{CCl}_{4}\) d. \(\mathrm{C}_{2} \mathrm{Cl}_{4}\)

Short answer

a. In Cl₂O, the bond angle between the central oxygen atom and adjacent chlorine atoms is approximately 104.5°. b. In NCl₃, the bond angle between the central nitrogen atom and adjacent chlorine atoms is approximately 107°. c. In CCl₄, the bond angle between the central carbon atom and adjacent chlorine atoms is 109.5°. d. In C₂Cl₄, the bond angle between any two adjacent chlorine atoms and the central carbon atom is 120°.

Step-by-step solution

a. Cl₂O

First, draw the Lewis structure for Cl₂O with each chlorine atom bonded to the oxygen atom: ``` Cl \ O / Cl ``` The oxygen atom has two lone pairs of electrons, making it's electron configuration: \( A E_{2} V \) (2 bonding sites and 2 lone electron pairs). Using the VSEPR theory, Cl₂O has a bent molecular geometry with an angle close to 109.5°. However, due to the repulsion of the lone pairs, the bond angle slightly decreases to around 104.5° between the chlorine and oxygen atoms.

b. NCl₃

Draw the Lewis structure for NCl₃: ``` Cl \ N - Cl / Cl ``` The nitrogen atom has one lone pair of electrons, and its electron configuration is: \( A E_{1} V_{3} \) (3 bonding sites and 1 lone electron pair). Using the VSEPR theory, NCl₃ forms a trigonal pyramidal molecular geometry. The bond angle between the chlorine and nitrogen atoms is approximately 107°.

c. CCl₄

Draw the Lewis structure for CCl₄: ``` Cl \ C - Cl / Cl - Cl ``` The carbon atom has no lone pair of electrons, and its electron configuration is: \( A E V_{4} \) (4 bonding sites and 0 lone electron pairs). Using the VSEPR theory, CCl₄ has a tetrahedral molecular geometry. The bond angle between the chlorine and carbon atoms is 109.5°.

d. C₂Cl₄

Draw the Lewis structure for C₂Cl₄: ``` Cl - C = C - Cl | X | Cl - C = C - Cl ``` We only need to consider one of the carbons as the central atom, as the bond angles are the same for both carbons. The carbon atom has no lone pair of electrons, and its electron configuration is: \( A E_{3} V_{1} \) (3 bonding sites and 0 lone electron pairs). Using the VSEPR theory, each carbon in C₂Cl₄ has a trigonal planar molecular geometry. The bond angle between any two adjacent chlorine atoms and the central carbon atom is 120°.

Key concepts

Molecular Geometry

Molecular geometry is an important concept in chemistry. It describes the three-dimensional shape that is formed by the atoms in a molecule. This shape is determined by the number of bonding groups and lone pairs surrounding a central atom. Each molecular structure has a distinct geometry, influencing many physical and chemical properties of the compound.

• Cl₂O has a bent geometry.
• NCl₃ forms a trigonal pyramidal shape.
• CCl₄ has a tetrahedral structure.
• C₂Cl₄ possesses a trigonal planar form for each carbon atom.

These geometrical arrangements are predicted by the Valence Shell Electron Pair Repulsion (VSEPR) theory, which states that electron pairs around a central atom will arrange themselves to minimize repulsion.

Bond Angles

Bond angles are the angles formed between two adjacent bonds at an atom within a molecule. They provide insight into the molecule's shape and are directly related to molecular geometry. Bond angles may vary due to the presence of lone pairs, which can repel more strongly than bonding pairs, hence affecting the angles.

For example:

• In Cl₂O, the bond angle is around 104.5°, slightly less than the typical 109.5° due to lone pair repulsion.
• NCl₃ features a bond angle of approximately 107°.
• In CCl₄, the bond angle is exactly 109.5° as there are no lone pairs to distort it.
• In C₂Cl₄, around each carbon, the bond angle is 120° due to the trigonal planar geometry.

Lewis Structure

The Lewis structure is a visual representation that shows the valence electrons of atoms within a molecule. These diagrams help in understanding how atoms are bonded together and the arrangement of electrons. By predicting how many bonds an atom can form, Lewis structures help deduce the molecule's shape and its potential reactivity.

Here's how Lewis structures are applied:

• For Cl₂O: Oxygen is the central atom with two bonding Cl atoms and two lone pairs.
• For NCl₃: Nitrogen shoKheads as the central atom, attached to three Cl atoms and one lone pair.
• For CCl₄: Carbon takes the center with four Cl atoms bonded around it and no lone pairs.
• For C₂Cl₄: Each carbon is sp² hybridized, forming a structure with Cl atoms and double bonds between carbons.

Lone Electron Pairs

Lone electron pairs, also known as non-bonding pairs, are pairs of valence electrons that are not shared with another atom in a covalent bond. These electrons occupy more space around the central atom than bonding pairs, leading to deviations in ideal bond angles. Their presence is crucial in understanding molecular geometry, as they cause repulsion that distorts ideal bond geometries.

Consider the impact of lone pairs in the following:

• Cl₂O: Oxygen's two lone pairs push the chlorine atoms together, reducing the bond angle to around 104.5°.
• NCl₃: The single lone pair on nitrogen slightly pushes the Cl atoms, reducing the ideal bond angle to about 107°.
• CCl₄: Lacks lone pairs, so the bond angle remains at the typical 109.5°.
• C₂Cl₄: Focus is more on the bonding framework. The angles are influenced by the central carbon atom and double bonding.