Question

Which of the following species has a molecular shape similar to that of ammonia, ${NH}_3$?

• A. ${BH}_3$
• B. $H_{2}O$
• C. $H_3{O}^{+}$
• D. ${CH}_4$
• E. ${NH}_4^{+}$

Answer 1

Answer: (C)

$H_3{O}^{+}$

Option C is the correct answer.

The number of valence electrons in $H_3{O}^{+}$ are ($3$ $+$ $6$ $-$ $1$), that is $8$. ($-1$ because the molecule contains a positive charge which means there is one electron less).

$N{H}_3$ also contains $8$ valence electrons.

Of the 8 valence electrons in $H_3{O}^{+}$, 6 are used up in making 3 single covalent bonds between oxygen and the hydrogen atoms. The remaining 2 electrons remain on the oxygen atom as a lone pair. The image is almost like ammonia.

Thus, three covalent bonds and one lone pair make the bond angle lesser than the usual tetrahedral angle. Hence, the molecule takes up the pyramidal shape like that of ammonia, because of the repulsion between bond pairs and lone pair. An image has been attached.