Question

Statement I: Since fluorine is more electronegative than nitrogen, the net dipole moment of NF3 is greater than NH3.
Statement II: In NH3, the orbital dipole due to the lone pair and the dipole moment of NH bonds are in opposite directions, but in NF3, the orbital dipole due to the lone pair and the dipole moments of N-F bonds are in the same direction.
In light of the above statements, choose the most appropriate from the options given below:

• A. Statement I is true but Statement II is false.
• B. Both Statement I and Statement II are false.
• C. Statement I is false but Statement II is are true.
• D. Both statement I and Statement II is are true.

Answer 1

Answer: (C)

Statement I is false but Statement II is are true.

Answer 2

Analysis of Statement I: NF3 does have a significant dipole moment due to the electronegativity of fluorine; however, because of the geometry of the molecule, the dipole moment of NH3 is actually greater. Thus, the assertion that the net dipole moment of NF3 is greater than NH3 is false.

Analysis of Statement II: In NH3, the presence of a lone pair on nitrogen results in a net dipole that is directed upwards, counteracting the downward dipole contributions from the N-H bonds. Therefore, the dipole moments do indeed work against each other. In NF3, the N-F bonds have their dipole moments aligned in the same direction as the lone pair dipole, thus reinforcing the overall dipole moment of the molecule. Hence, this statement is true.

Considering both analyses: Statement I is false, while Statement II is true, leading to the conclusion.