The series of oxyanions XO₄²⁻ (where X is a Group 6A or 7A element in its highest common oxidation state) includes SO₄²⁻, SeO₄²⁻, and ClO₄⁻. Pauling electronegativity values are: S 2.5, Se 2.4, Cl 3.0, and O 3.5.
(a) Calculate the average ΔEN for an X–O bond in each oxyanion.
(b) For each oxyanion, predict whether the X–O bond is better described as predominantly ionic or covalent. Provide a rationale that refers explicitly to the magnitude of ΔEN and to the non-metallic character of the central atom.
(c) The X–O bonds in these oxyanions are often described as having significant multiple-bond character, even though the Lewis structures are drawn with single bonds. Discuss how electronegativity considerations and resonance can together account for this description.
(d) Suppose an unknown oxyanion PO₄³⁻ is analyzed. Without performing additional calculations, compare the expected ionic character of a P–O bond to that of each X–O bond in parts (a)–(c) and justify your comparison based on periodic trends in electronegativity.