Question

Predict the molecular structure (including bond angles) for each of the following. a. \(\mathrm{PCl}_{3}\) b. \(\mathrm{SCl}_{2}\) c. \(\mathrm{SiF}_{4}\)

Short answer

The molecular structures and bond angles for the given compounds are as follows: a. PCl3 has a tetrahedral shape with a bond angle slightly less than 109.5° due to the presence of a lone pair. b. SCl2 has a bent shape with a bond angle less than 109.5° due to the presence of two lone pairs. c. SiF4 has a tetrahedral shape with a bond angle of 109.5°.

Step-by-step solution

a. PCl3 molecular structure

To predict the molecular structure and bond angles of PCl3, follow these steps: 1. Draw the Lewis structure for PCl3: P is the central atom with 5 valence electrons and each Cl has 7 valence electrons. Lewis structure: P surrounded by 3 Cl atoms, with a single bond between P and each Cl atom. P has one lone pair of electrons. 2. Identify the shape of the molecule based on the number of electron domains P has 3 bond pairs (from P-Cl bonds) and 1 lone pair, which means there are 4 electron domains. According to the VSEPR theory, this molecular geometry is called tetrahedral. 3. Determine the bond angles based on the shape of the molecule The bond angles in a tetrahedral shape are idealistically 109.5°. However, the lone pair slightly increases the repulsion and decreases the bond angles. Therefore, the bond angle for PCl3 is slightly less than 109.5°.

b. SCl2 molecular structure

To predict the molecular structure and bond angles of SCl2, follow these steps: 1. Draw the Lewis structure for \(\mathrm{SCl}_{2}\): S is the central atom with 6 valence electrons and each Cl has 7 valence electrons. Lewis structure: S surrounded by 2 Cl atoms, with a single bond between S and each Cl atom. S has two lone pairs of electrons. 2. Identify the shape of the molecule based on the number of electron domains: S has 2 bond pairs (from S-Cl bonds) and 2 lone pairs, which means there are 4 electron domains. According to the VSEPR theory, this molecular geometry is called bent. 3. Determine the bond angles based on the shape of the molecule: The bond angles in a bent shape with four electron domains are idealistically 109.5°. However, the lone pairs increase the repulsion and decrease the bond angles. Therefore, the bond angle for \(\mathrm{SCl}_{2}\) is less than 109.5°.

c. SiF4 molecular structure

To predict the molecular structure and bond angles of \(\mathrm{SiF}_{4}\), follow these steps: 1. Draw the Lewis structure for \(\mathrm{SiF}_{4}\): Si is the central atom with 4 valence electrons and each F has 7 valence electrons. Lewis structure: Si surrounded by 4 F atoms, with a single bond between Si and each F atom. Si has no lone pairs of electrons. 2. Identify the shape of the molecule based on the number of electron domains: Si has 4 bond pairs (from Si-F bonds) and no lone pairs, which means there are 4 electron domains. According to the VSEPR theory, this molecular geometry is called tetrahedral. 3. Determine the bond angles based on the shape of the molecule: The bond angles in a tetrahedral shape are idealistically 109.5°. Thus, the bond angle for \(\mathrm{SiF}_{4}\) is 109.5°.