Final answer:
The best Lewis structure for C₂H₃O⁻ features a double bond between carbon and oxygen, with the oxygen also carrying two lone pairs and the negative charge. The octet rule is satisfied for all atoms except hydrogen, which follows the duet rule.
Step-by-step explanation:
To choose the best Lewis structure for C₂H₃O⁻, we must first consider the total number of valence electrons. For this molecule, carbon atoms contribute 4 electrons each, hydrogen atoms contribute 1 electron each, and the oxygen atom contributes 6 electrons, with an additional electron due to the negative charge for a total of 16 valence electrons. In constructing the Lewis structure, place carbon atoms in the center, bind them to the oxygen and hydrogen atoms, satisfy the octet rule for carbon and oxygen, and ensure hydrogen atoms follow the duet rule.
An optimal Lewis structure might show a double bond between one of the carbon atoms and the oxygen atom, with the remaining bonds being single. This double bond is because oxygen typically forms double bonds with carbon to achieve a full octet. The final structure would have one carbon atom double-bonded to oxygen with two lone pairs on oxygen, and both carbon atoms single-bonded to hydrogen atoms. The negative charge is typically placed on the more electronegative atom, which is oxygen in this case.