What is the bond order of the phosphate–oxygen bonds within the phosphate ion, PO₄^3–?

• A. 1.25
• B. 2
• C. 2.5
• D. 1

Answer: (A)

Verified step by step guidance

1. Understand that bond order is the number of chemical bonds between a pair of atoms. In the case of resonance structures, bond order is the average number of bonds between the atoms across all resonance structures.
2. Recognize that the phosphate ion, \( \text{PO}_4^{3-} \), has resonance structures. Each phosphorus atom is bonded to four oxygen atoms, and the negative charge is distributed among the oxygen atoms.
3. Draw the resonance structures for \( \text{PO}_4^{3-} \). In each structure, one of the P-O bonds is a double bond, while the others are single bonds. There are four possible resonance structures.
4. Calculate the bond order by averaging the bond types across the resonance structures. Since there are four resonance structures, and each has one double bond and three single bonds, the total number of bonds is 5 (1 double bond + 3 single bonds) per structure.
5. Divide the total number of bonds by the number of resonance structures to find the bond order: \( \text{Bond Order} = \frac{5}{4} = 1.25 \).