Three alternative Lewis diagrams have been proposed for the phosphate ion, PO₄³⁻
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Three alternative Lewis diagrams have been proposed for the phosphate ion, PO₄³⁻. Each description refers to the same central phosphorus atom surrounded by four oxygen atoms.
Diagram A:
• Four single P–O bonds.
• Phosphorus has one lone pair.
• Each oxygen has three lone pairs, and no formal charges are shown.
Diagram B:
• One P=O double bond and three P–O single bonds.
• Phosphorus has no lone pairs.
• The doubly bonded oxygen has two lone pairs; each singly bonded oxygen has three lone pairs and carries a negative formal charge.
Diagram C:
• Two P=O double bonds and two P–O single bonds.
• Phosphorus has no lone pairs.
• Each doubly bonded oxygen has two lone pairs; each singly bonded oxygen has three lone pairs and carries a negative formal charge.
Analyze the validity of these proposed structures.
(a) For each diagram, determine whether the total number of valence electrons depicted matches the required total for PO₄³⁻. Support your answer with calculations.
(b) For each diagram, state whether any atom violates the octet rule and identify the specific violation(s), if present.
(c) Select the diagram that provides the best single-structure representation of PO₄³⁻. Justify your selection by comparing formal charges and octet compliance across the three diagrams.
(d) Draw the complete set of equivalent resonance structures implied by the best diagram in part (c), and explain how resonance contributes to the observed equal P–O bond lengths in phosphate salts.