Naming Ionic Compounds with Polyatomic Ions

Introduction

• Monatomic Ions: Previously learned naming and deducing formulas for compounds made from one-atom ions (monatomic).
• Polyatomic Ions: Ions composed of more than one atom.
  • "Mono" means one, "Poly" means many.
  • Examples: Hydroxide, sulfate, nitrate, phosphate, carbonate, ammonium.
  • Except for ammonium (cation), listed polyatomic ions are anions.

Important Concepts

• Remember the formula and charges of common polyatomic ions.

Examples

Example 1: Sodium Nitrate

1. Ions: Sodium Ion (Na⁺) and Nitrate Ion (NO₃⁻)
2. Method: Crisscross charges to deduce formula.
   • Formula: NaNO₃
3. Naming: Combine names as they are.
   • Name: Sodium Nitrate

Example 2: Magnesium Hydroxide

1. Ions: Magnesium Ion (Mg²⁺) and Hydroxide Ion (OH⁻)
2. Method: Crisscross charges, ensure two hydroxide ions balance the +2 charge.
   • Use brackets for polyatomic ions when more than one is needed.
   • Formula: Mg(OH)₂
3. Naming: Maintain structure of hydroxide ion.
   • Name: Magnesium Hydroxide

Example 3: Potassium Sulfate

1. Ions: Potassium Ion (K⁺) and Sulfate Ion (SO₄²⁻)
2. Method: Two potassium ions needed to balance -2 charge.
   • Formula: K₂SO₄
3. Naming: Combine names.
   • Name: Potassium Sulfate

Special Cases: Transition Metals

• Multivalent Metals: Can have multiple possible charges.
  • Example: Copper can be Cu⁺ or Cu²⁺.
• Naming: Specify valency using Roman numerals.
  • Example: For CuCl₂, name is Copper (II) Chloride.

Practice

• Find the formula and name for combinations like potassium and sulfate.
• Use crisscross method to ensure neutral overall charge in compounds.

Conclusion

• Understanding and remembering polyatomic ions and applying crisscross method is crucial for naming and deducing formulas of ionic compounds.