Question

For which of the following molecules, resonance structures are necessary to describe the bonding satisfactorily?

• A. Ozone
• B. Boron trifluoride
• C. Water
• D. Acetylene
• E. Phosphorus trichloride

Hint:

Resonance structures are required for molecules where the bonding cannot be accurately described by a single structure. Ozone is a key example of a molecule that needs resonance to account for its electron delocalization.

Answer 1

The Correct Option is A

Resonance structures are used to represent molecules that cannot be accurately described by a single classical structure. They are necessary when a molecule has delocalized electrons, where the bonding cannot be fully captured by one single structure.
A) Ozone (O₃):
Ozone is a classic example where resonance structures are necessary. The bonding in ozone is best described by two resonance structures, where the double bond and single bond are delocalized, and the actual molecule is a hybrid of these structures. This delocalization of electrons cannot be described by just one structure, making resonance structures essential.
B) Boron trifluoride (BF₃):
Boron trifluoride does not require resonance structures. It has an electron-deficient boron atom, but it does not exhibit resonance because the bonding can be adequately described by a single structure.
C) Water (H₂O):
Water does not require resonance structures. The bonding in water can be described with a single structure where the oxygen atom is bonded to two hydrogen atoms via single bonds.
D) Acetylene (C₂H₂):
Acetylene (ethyne) does not require resonance structures. The bonding in acetylene is straightforward with a triple bond between the two carbon atoms and single bonds to hydrogen atoms.
E) Phosphorus trichloride (PCl₃):
Phosphorus trichloride does not require resonance structures. The bonding in PCl₃ can be described with a single structure where phosphorus is bonded to three chlorine atoms via single bonds.
Thus, the correct answer is option (A), Ozone.