Discussion Forum



1)

Which is the correct order of dipole moments  of $BF_{3},NF_{3} $ and $NH_{3}$?


A) $ NH_{3} > BF_{3}>NF_{3}$

B) $BF_{3} > NF_{3} > NH_{3}$

C) $NH_{3} > NF_{3} > BF_{3}$

D) $NF_{3} > NH_{3} > BF_{3}$

Answer:

Option C

Explanation:

 $BF_{3}$, has zero dipole moment

  1672021875_c1.PNG

In $NH_{3}$, N is more electronegative  than H. So, nitrogen  pulls the electron from H towards itself and the direction of moment is same due to N-H  bond as that of the lone pair of electrons on nitrogen

                       1672021186_c2.PNG                       

                                                                    $\mu _{net}=1.46 D$

  In $NF_{3}$ , F is more electronegative than N, All F atoms pull the electrons towards themselves and resultant dipole moment is opposite to the direction of that of the lone pair at N atom, Hence , net dipole moment decreases.

              1672021544_c3.PNG

                                   $\mu _{net}=0.24 D$

 Therefore, dipole ment of $NH_{3}$  is greater than $NF_{3}$  . Hence  , order  of dipole moment is 

$NH_{3} > NF_{3} > BF_{3}$