question_answer

The electronegativity difference between N and F is greater than that between N and H yet the dipole moment of \[N{{H}_{3}}\] (1.5 D) is larger than that of \[N{{F}_{3}}\] (0.2 D). This is because:            [AIPMT (S) 2006]

A)  in \[N{{H}_{3}}\] as well as in \[N{{F}_{3}}\] the atomic dipole and bond dipole are in the same direction

B)       in \[N{{H}_{3}}\] the atomic dipole and bond dipole are in the same direction whereas in \[N{{F}_{3}}\] these are in opposite directions

C)       in \[N{{H}_{3}}\] as well as \[N{{F}_{3}}\] the atomic dipole and bond dipole are in opposite directions

D)       in \[N{{H}_{3}}\] the atomic dipole and bond dipole are in the opposite directions whereas in \[N{{F}_{3}}\]these are in the same directions

Correct Answer: B

Solution :

Electronegativity of N is greater than that of H, but in \[N{{F}_{3}}\] electronegativity of F is greater than that of N. So, in \[N{{H}_{3}}\] the atomic dipole and bond dipole are in the same direction whereas in \[N{{F}_{3}}\] these are in opposite directions.