would you expect the nonbonding electron pair domain in nh3 to be greater or less in size than for the corresponding one in PH3?
According to MasteringChemistry, it is lesser.
Less
Take your pick.
http://www.google.com/search?q=bond+angles+NH3+and+PH3&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
To determine whether the nonbonding electron pair domain in NH3 (ammonia) is greater or less in size than in PH3 (phosphine), we need to consider the atomic properties of nitrogen (N) and phosphorus (P) atoms.
The size or volume of an atom is determined by its atomic radius. Nitrogen (N) has a smaller atomic radius than phosphorus (P) because nitrogen has a smaller number of electrons and protons, resulting in a smaller electron cloud.
When ammonia (NH3) and phosphine (PH3) molecules are formed, a central atom (nitrogen or phosphorus) is bonded to three hydrogen atoms with an unshared pair of electrons. These unshared pairs are commonly referred to as nonbonding electron pairs or lone pairs.
Due to nitrogen's smaller atomic radius, the nonbonding electron pair domain in NH3 is expected to be relatively smaller compared to the corresponding one in PH3. The larger atomic radius of phosphorus allows for greater electron cloud size, leading to a larger nonbonding electron pair domain in PH3.
In summary, the nonbonding electron pair domain in NH3 is expected to be smaller in size compared to the corresponding one in PH3 due to the differences in atomic radius between nitrogen and phosphorus.