Question

How is phosphine’s (${\mathbf{\text{PH}}}_{\mathbf{\text{3}}}$) structure different from that of ammonia?

Short answer

Phosphine and ammonia vary in that the lone pairs on the phosphorus atom take up more space than the lone pairs on the nitrogen atom. Furthermore, the interactions that separate the core atoms nitrogen and phosphorus from hydrogen make them distinct.

Step-by-step solution

Concept Introduction

A chemist specifies the molecular geometry and, where feasible and essential, the electronic structure of the target molecule or other solid during a chemical structure determination.

The angle created by three atoms across at least two bonds is known as a bond angle. The torsional angle is the angle produced between the first three atoms and the plane formed by the final three atoms for four atoms linked together in a chain.

Structure of Phosphine and Ammonia

To understand the difference of phosphine's structure with ammonia, let us consider the concept of the bondangles.

Phosphine or${\text{PH}}_3$has a molecular structure of a trigonal pyramidal having a bond angle of$93.5$degrees betweenhydrogen-phosphorus-hydrogen bonds.

On the other hand, in ammonia or${\text{NH}}_3$, it also has a trigonal pyramidal shape having a bond angle between thehydrogen-nitrogen-hydrogen bond of$107.3$degrees.

Therefore, the lone pairs that exists on the phosphorus atom will takeup more space in comparison to nitrogen's lone pairs.

Atomic Size of Phosphine and Ammonia

Also, we can consider the sizes of the central atom. For phosphine, the central atom is phosphorus and for ammonia, it isnitrogen.

Since phosphorus has a larger size in comparison to nitrogen, there will be a greater attraction in ammonia since there isnot a lot of atomic size difference resulting to nitrogen steadily holding its hydrogen atoms. This makes ammonia morestable than phosphine.

Therefore, the forces between the central atoms nitrogen and phosphorus to hydrogen respectively makes them differentfrom each other