Question

NH3 has greater dipolemoment than NF3. why?

Answer 1

we know , in symmetrical structure dipolemoment is zero , because all charges cancelled each other .

now, see structure NH3 , and find out lone pair .
e.g no of lone pair = 1
we know, if any molecule have lone pair , it means this molecule isn't symmetry .e.g dipope moment isn't zero.

now, see structure of NF3 , and lone pair =1 , hence, this is symmetry. so, it's dipole moment isn't zero.
but according to VESPER theory, if any atom surrounded by more electronegative atoms then bigger bond angle , hence less dipole moment.
here in NF3 , N is surrounded by F and in NH3 , N is surrounded by H.F is more electronegative elements then H
so, NH3 has greater dipole moment then NF3

Answer 2

Answer:

In NH3 the orbital dipol due to lone pair and resultant dipol momentum os N-H bonds are in he same direction.

IN Nf3 orbitals dipole down to lone pair and  the  resut  dipole  moment of N-F bonds are in oppositr direction.