question_answer

Which of the following molecules has the maximum dipole moment? [AIPMT 2014]

A)  \[C{{O}_{2}}\]           

B)  \[C{{H}_{4}}\]

C)  \[N{{H}_{3}}\]   

D)  \[N{{F}_{3}}\]

Correct Answer: C

Solution :

\[C{{O}_{2}}\]and \[C{{H}_{4}}\] have zero dipole moment as these are symmetrical in nature. Between \[N{{H}_{3}}\] and \[N{{F}_{3}},\,N{{F}_{3}}\] has greater dipole moment though in \[N{{H}_{3}}\]and \[N{{H}_{3}}\]both, N possesses one lone pair of electrons. This is because in case of \[N{{H}_{3}}\], the net N?H bond dipole is in the same direction as the  direction of dipole of lone pair but in case of \[N{{H}_{3}}\], the direction of net bond dipole of three ?N?F bonds is opposite the that of the dipole of the lone pair.                                   \[\because \]\[{{\mu }_{res}}={{\mu }_{1}}+{{\mu }_{2}}+{{\mu }_{3}}=-{{\mu }_{res}}=-{{\mu }_{4}}=0\]           \[\therefore \]\[{{\mu }_{net}}={{\mu }_{1}}+{{\mu }_{2}}+{{\mu }_{3}}+{{\mu }_{4}}\]       \[=-{{\mu }_{4}}+{{\mu }_{4}}=0\]