Question

Identify the correct statements from the following.
(1) The dipole moment of $CO _{2}$ and $BF _{3}$ is zero.
(2) The dipole moment of $NF _{3}$ is higher than the dipole moment of $NH _{3}$.
(3) The dipole moment of $HI$ is lower than the dipole moment of $HCl$.

• A. 1,3
• B. 1,2
• C. 2,3
• D. 1,2,3

Answer 1

Answer: (A)

1 . The $BF _{3}$ molecule has a symmetrical trigonal planar geometry, the moment of any two $B - F$ dipoles is equal in magnitude but opposite in direction to the moment of the $BF _{3}$ molecule is zero. Same as $CO _{2}$.

2. In $NH _{3}, N$ is more electronegative than $H$ so, $N$ pulls the electrons from H towards itself so, the direction of moment due to the $N - H$ bonds is in the same direction as that of the lone pair of electrons on nitrogen.



But in case of $NF _{3}, H -\bullet$ [lone pair] moment is in the opposite direction to the $N - F$ bond moments.

Thus, has smaller net dipole moment.

3. $\because$ Size of I-atom is more than of Cl-atom and electronegativity of I-atom is less than of Cl-atom. Hence, HI has lower dipole-moment than HCl.