Question

Explain why PH3 is a much weaker base than NH3

Answer 1

In NH3 central atom nitrogen has small size. So the repulsion between lone pair and bond pair is more in nitrogen.

Nitrogen easley donate lone pair of electrons. NH3 is strong lewis base.

In PH3 central atom phsophours has large size. So the the repulsion between lone pair and bond pair is less in phosphorous. Phsophorous not easley donate lone pair of electrons. PH3 is weak base.

NH3 is strong base than PH3.

VA group hydrides

   NH3

   PH3

   AsH3

SbH3

   BiH3

in group top to bottom central atom of hydrides increases. When size of the central atom is increases the donate capacity of lone pair of electrons decreases.So basecity of hydrides in a group top to bottom decreases.

PH3 is a much weaker base than NH3