Question

based on the lewis diagram for nh₃ shown above, the h - n - h bond angle is closest to which of the following?
a 60°
b 90°
c 109.5°
d 120°

Explanation:

Step1: Determine the electron - pair geometry and molecular geometry of \(NH_3\)

• The central atom \(N\) in \(NH_3\) has 4 electron - pairs (3 bonding pairs and 1 lone pair).
• According to VSEPR (Valence - Shell Electron - Pair Repulsion) theory, the electron - pair geometry is tetrahedral (ideal bond angle \(109.5^{\circ}\)).
• But due to the repulsion between the lone pair and bonding pairs, the molecular geometry is trigonal pyramidal. The lone pair - bond pair repulsion is stronger than bond pair - bond pair repulsion, so the bond angle is slightly less than \(109.5^{\circ}\).

Step2: Compare with the given options

• Option A (\(60^{\circ}\)) is too small.
• Option B (\(90^{\circ}\)) is incorrect as it does not match the trend of VSEPR - predicted angles for \(NH_3\).
• Option D (\(120^{\circ}\)) would be for a trigonal planar electron - pair geometry (which \(NH_3\) does not have).
• The bond angle in \(NH_3\) is close to \(109.5^{\circ}\) (slightly less due to lone - pair effects), and among the given options, \(109.5^{\circ}\) (Option C) is the closest based on VSEPR - predicted ideal tetrahedral electron - pair geometry before considering the slight distortion from the lone pair.

Answer:

C. \(109.5^{\circ}\)