Lecture Notes: Polyatomic Ions

Introduction

• Polyatomic Ions: Groups of atoms that carry a charge.
• Mostly anions except for ammonium, which is a cation.

Key Polyatomic Ions

• Ammonium (NH₄⁺): Only cation in the list.

Memorizing Strategies

'Ate' Ions

• Memorize ions ending in -ate:
  • Sulfate (SO₄²⁻)
  • Chlorate (ClO₃⁻)
  • Nitrate (NO₃⁻)
  • Phosphate (PO₄³⁻)

Conversion Rules

• -ite suffix: Same charge as 'ate' but one less oxygen.
  • Chlorite: ClO₂⁻
  • Sulfite: SO₃²⁻
  • Nitrite: NO₂⁻
• Prefixes:
  • Hypo-: One less oxygen than -ite (e.g., Hypochlorite: ClO⁻)
  • Per-: One more oxygen than -ate (e.g., Perchlorate: ClO₄⁻)

Hydrogen or Bi- Prefix

• Add H⁺ to the ion, increasing the charge by 1.
  • Bisulfate (HSO₄⁻): Derived from sulfate
  • Bisulfite (HSO₃⁻): Derived from sulfite
  • Hydrogen phosphate (HPO₄²⁻): Derived from phosphate
  • Dihydrogen phosphate (H₂PO₄⁻): Derived from two additions of H⁺
  • Bicarbonate (HCO₃⁻): Derived from carbonate (CO₃²⁻)

Important Ions

• Acetate (C₂H₃O₂⁻ or CH₃CO₂⁻): Structural formula is preferred.
• Hydroxide (OH⁻)
• Chromate (CrO₄²⁻) and Dichromate (Cr₂O₇²⁻)
• Cyanide (CN⁻)
• Peroxide (O₂²⁻)

Additional Notes

• Remember to work on the table of ions for future classes.
• Acetate is often written structurally as CH₃CO₂⁻.
• Ammonium formation: Ammonia (NH₃) with an added H⁺ becomes NH₄⁺.

Closing Remarks

• Utilize these tricks for memorization.
• Be prepared to use these ions in future lessons.
• Stay safe and keep cool. Goodnight!