Question

Among the following which has trigonal pyramidal geometry?

• A. ${BH}_3$
• B. $H_{2}O$
• C. ${CH}_4$
• D. ${NH}_3$
• E. $Al{Cl}_3$

Answer 1

The correct option is D ${NH}_3$


An example of trigonal pyramid molecular geometry that results from tetrahedral electron pair geometry is $N{H}_3$. The nitrogen has 5 valence electrons and thus needs 3 more electrons from 3 hydrogen atoms to complete its octet. This then leaves a lone electron pair that is not bonded to any other atom. The three hydrogen atoms and the lone electron pair are as far apart as possible at nearly ${109}^o$ bond angle. This is tetrahedral electron pair geometry.
The lone electron pairs exerts a little extra repulsion on the three bonding hydrogen atoms to create a slight compression to a ${107}^o$ bond angle