Which pair of Lewis structures is NOT a pair of resonance structures?

• A. Carbonate ion: O–C(=O)–O and O=C–O–O
• B. Ethene: H2C=CH2 and H3C–CH3
• C. Ozone: O=O–O and O–O=O
• D. Nitrite ion: O–N=O and O=N–O

Answer: (B)

Verified step by step guidance

1. Step 1: Understand what resonance structures are. Resonance structures are different Lewis structures for the same molecule or ion that differ only in the placement of electrons (usually pi electrons or lone pairs), not in the arrangement of atoms. The actual structure is a hybrid of these resonance forms.
2. Step 2: Examine each pair of Lewis structures to see if they have the same arrangement of atoms but differ only in electron placement. For example, in the carbonate ion (CO3^2-), the atoms remain connected in the same order, but the double bond shifts among the oxygen atoms, indicating resonance.
3. Step 3: Check the ethene (H2C=CH2) and ethane (H3C–CH3) pair. Notice that these two structures differ in the connectivity of atoms: ethene has a double bond between carbons, while ethane has a single bond and extra hydrogens. This means they are not resonance structures but different molecules.
4. Step 4: For ozone (O3), the two Lewis structures differ only in the placement of the double bond and lone pairs, with the same atom connectivity, so they are resonance structures.
5. Step 5: For the nitrite ion (NO2^-), the two Lewis structures differ in the position of the double bond and lone pairs but have the same atom connectivity, indicating resonance structures.