Question

Bond angle of NH3 is 1070. Why?

Answer 1

In ammonia molecule, the central nitrogen atom (Z=7, 1s2 2s2 2p3) has five valence electrons. Three of these valence electrons share electrons with hydrogen atoms forming three bond pairs around the nitrogen atom. The remaining two electrons are present as lone pair. Thus, in ammonia, nitrogen is surrounded by four electron pairs (three bond pairs and one lone pair). These four electron pairs adopt tetrahedral geometry. But all the four electron pairs around nitrogen are not equivalent ​(three bond pairs and one lone pair). and therefore, ammonia has distorted tetrahedral geometry. The bond angle will not be 109.5° but it is 107° . This distortion is due to the presence of one lone pair in addition to bond pairs. As lone pair-bond pair repulsion is more than bond pair-bond pair repulsion. As a result, the lone pair electron will repel bond pairs strongly and bond angle decreases to 107°. The geometry of ammonia molecule is regarded as pyramidal.