What is the hybridization of each carbon atom in the oxalate ion $C_2{O}_4{-}^2$?

• A. $\mathrm{sp}$
• B. ${\mathrm{sp}}^3$
• C. ${\mathrm{sp}}^2$
• D. One carbon is $\mathrm{sp}$ and the other is ${\mathrm{sp}}^2$

Answer: (C)

Verified step by step guidance

1. Draw the Lewis structure of the oxalate ion \( \mathrm{C_2O_4^{2-}} \), showing all atoms, bonds, and formal charges. Remember that the ion carries a -2 charge, which affects the total number of valence electrons.
2. Identify the bonding environment around each carbon atom by counting the number of atoms bonded to it and the number of lone pairs (if any). This will help determine the steric number, which is the sum of sigma bonds and lone pairs around the carbon.
3. Recall that the hybridization of a carbon atom depends on its steric number: \( sp \) for steric number 2, \( sp^2 \) for steric number 3, and \( sp^3 \) for steric number 4.
4. Examine the resonance structures of the oxalate ion to see if the bonding around the carbon atoms is equivalent or if there are differences that might lead to different hybridizations for each carbon.
5. Based on the steric number and resonance considerations, assign the hybridization to each carbon atom. Typically, in oxalate, each carbon is bonded to two oxygens and one carbon, with no lone pairs, leading to a trigonal planar geometry and \( sp^2 \) hybridization.