Sulfate ion template

SO₄²⁻: three of the six equivalent expanded-octet forms with two S=O and two S–O⁻ (the usual textbook drawing), and the octet form with S²⁺ and four S–O⁻ reached by moving the S=O π bonds onto oxygen.

What the template shows

• Textbook expanded-octet forms (two S=O) and the octet form with S²⁺
• expanded octet
• Resonance contributors
• Expanded-octet forms
• Textbook convention: two S=O, two S–O⁻ (3 of 6 forms)
• Octet form
• Moving the S=O π bonds onto O: S²⁺, four S–O⁻
• Convention: school and many university texts draw sulfate with two S=O bonds (twelve electrons on S), which minimises formal charges; there are six such equivalent forms.
• Modern bonding analysis favours the octet form (S²⁺, four S–O⁻) with very polar bonds; sulfur d orbitals play little part.
• Every description gives four equal S–O bonds (about 149 pm) in a tetrahedral ion, with each oxygen carrying −½ of the charge.
• Total charge is −2 in every form.
• Contributors are not in equilibrium: the real species is one hybrid of them · every part of this figure is editable

Drawn with 30 atoms, 10 arrows, 3 shapes – every one editable in MolDraw.

Sources

• Housecroft & Sharpe, Inorganic Chemistry, 5th ed., Pearson 2018 Textbook