The oxalate ion, C2O42-, is an intriguing polyatomic ion that showcases resonance and unique bond orders. Here’s how to approach this question.
a) Drawing the Lewis Structure and Equivalent Resonance Structures
To draw the Lewis structure for the oxalate ion, we start by counting the total number of valence electrons. Carbon has 4 valence electrons, and oxygen has 6. For C2O42-:
- Valence electrons from 2 Carbon atoms: 2 x 4 = 8
- Valence electrons from 4 Oxygen atoms: 4 x 6 = 24
- Charge contribution: 2 electrons from the -2 charge
Thus, total valence electrons = 8 + 24 + 2 = 34 electrons.
Next, we arrange the molecules, placing the carbon atoms centrally conected to the oxygen atoms. A common structure would feature each carbon atom double-bonded to two oxygen atoms (two C=O) and single-bonded to another oxygen atom (two C–O). The two single-bonded oxygens carry negative charges.
Here’s one possible Lewis structure:
Resonance occurs as the placement of double bonds can shift between the different oxygen atoms. There are several equivalent resonance structures that can be drawn, each redistributing the double bond among the oxygen atoms while maintaining the overall charge and structure.
b) Are All Carbon-Oxygen Bonds the Same in This Ion?
No, not all carbon-oxygen bonds in the oxalate ion are the same. In the resonance structure, we have:
- Two C=O double bonds
- Two C–O single bonds
For the bond order:
- The bond order for each C=O bond is 2 (due to the double bond).
- The bond order for each C–O bond is 1 (due to the single bond).
To determine the bond order for the overall oxalate ion, we can average the bond types because of resonance:
- Each carbon is bonded to four oxygens total, consisting of 2 double bonds and 2 single bonds, leading to a calculated bond order of 1.5 for all four bonds when averaged.
In summary:
- Bond Order for C=O: 2
- Bond Order for C–O: 1
- Average Bond Order in C2O4^2-: 1.5
This illustrates the unique hybridization and bond characteristics within the oxalate ion.