question_answer

                                                          \[N{{F}_{3}}\]and\[N{{H}_{3}}\] are both pyramidal but differ widely in dipole moment values. Assign reason.

Answer:

                Both \[N{{F}_{3}}\] and \[N{{H}_{3}}\] molecules have pyramidal geometries and their bond angles are also quite close (102° and 107° respectively). But the dipole moment of \[N{{H}_{3}}\] is 1.49D while that of \[N{{F}_{3}}\] is only 0.24D. This is mainly due to the reason that the dipole moments of N-F bonds in \[N{{F}_{3}}\] molecule oppose the dipole moment because of lone pair while in \[N{{H}_{3}}\] molecule, the dipole moments of N-H bonds and lone pair reinforce. Thus, ammonia has more dipole moment than \[N{{F}_{3}}\]. Because of the same reason, \[N{{F}_{3}}\] cannot act as Lewis base just like \[N{{H}_{3}}\].