Question

Which of the following statement is INCORRECT?

• A. The dipole moment of $BF_{3}$ is zero.
• B. The bond order of CO molecule is the same as the bond order in $NO^{+}$ ion.
• C. In ozone molecule, the two O-O bond lengths are equal.
• D. The dipole moment of $NF_{3}$ is much greater than that in $NH_{3}$
• E. Carbonate ion has three canonical forms.

Hint:

In $NH_{3}$, $\mu$ directions add up; in $NF_{3}$, they partially cancel.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
We need to evaluate five statements related to molecular geometry, bonding, dipole moments, and resonance to identify the incorrect one.
Step 2: Detailed Explanation:
Let's analyze each statement: - (A) The dipole moment of BF\(_3\) is zero: Boron trifluoride (BF\(_3\)) has a trigonal planar geometry. The B-F bonds are polar, but due to the symmetrical arrangement of the three bonds at 120° to each other, the individual bond dipoles cancel out completely. Thus, the net dipole moment of the molecule is zero. This statement is correct. - (B) The bond order of CO molecule is the same as the bond order in NO\(^+\) ion: Carbon monoxide (CO) has 6 + 8 = 14 electrons. The NO\(^+\) ion has 7 + 8 - 1 = 14 electrons. Species with the same number of electrons (isoelectronic) have the same molecular orbital configuration and thus the same bond order. The bond order for 14-electron species like N\(_2\), CO, and NO\(^+\) is 3. This statement is correct. - (C) In ozone molecule, the two O-O bond lengths are equal: The ozone molecule (O\(_3\)) exhibits resonance. It is a resonance hybrid of two structures: O=O-O\(^-\) \( \leftrightarrow \) \(^-\)O-O=O. Due to this resonance, the two O-O bonds are identical and have a bond length that is intermediate between a single and a double bond. This statement is correct. - (D) The dipole moment of NF\(_3\) is much greater than that in NH\(_3\): Both NF\(_3\) and NH\(_3\) have a trigonal pyramidal geometry with a lone pair on the central nitrogen atom. - In NH\(_3\), the N-H bond dipoles point towards the more electronegative nitrogen atom. The dipole of the lone pair also points "upwards". All these dipoles add up, resulting in a significant net dipole moment (approx. 1.47 D). - In NF\(_3\), fluorine is more electronegative than nitrogen. The N-F bond dipoles point away from the nitrogen, towards the fluorine atoms. The dipole of the lone pair still points "upwards". The bond dipoles and the lone pair dipole are in opposite directions, so they partially cancel each other out. This results in a much smaller net dipole moment (approx. 0.23 D) for NF\(_3\). Therefore, the statement that the dipole moment of NF\(_3\) is much greater than that of NH\(_3\) is incorrect. - (E) Carbonate ion has three canonical forms: The carbonate ion (CO\(_3^{2-}\)) has a central carbon double-bonded to one oxygen and single-bonded to two negatively charged oxygens. The double bond can be delocalized over all three oxygen atoms, leading to three equivalent resonance structures (canonical forms). This statement is correct. Step 4: Final Answer:
The incorrect statement is (D).