Writing Ionic Compounds

Key Concepts

• Ionic compounds are composed of metals and nonmetals.
• Charges must be balanced to write the correct formula.
• These are often referred to as binary ionic compounds because they consist of only two types of elements.

Example 1: Calcium Fluoride (CaF₂)

• Calcium (Ca) is a metal with a charge of 2+ (Ca²⁺).
• Fluorine (F) becomes Fluoride with a charge of 1- (F⁻).
• To balance charges:
  • Calcium: 2+
  • Fluoride: 1-
  • Two Fluorine atoms are needed to balance one Calcium atom: CaF₂.

Example 2: Magnesium Oxide (MgO)

• Magnesium (Mg) is a metal with a charge of 2+ (Mg²⁺).
• Oxygen becomes Oxide with a charge of 2- (O²⁻).
• Charges are already balanced:
  • Magnesium: 2+
  • Oxide: 2-
• Formula: MgO (without subscript means 1 atom each)

Example 3: Strontium Phosphide (Sr₃P₂)

• Strontium (Sr) is a metal with a charge of 2+ (Sr²⁺).
• Phosphorus becomes Phosphide with a charge of 3- (P³⁻).
• Balance charges:
  • Add more Phosphide to reach a total charge of 6-.
  • Add more Strontium to reach a total charge of 6+:
    • 3 Strontium (2+ each) = 6+
    • 2 Phosphide (3- each) = 6-
• Formula: Sr₃P₂

Notes on Binary Ionic Compounds

• Binary indicates two types of elements.
• Even if the compound contains more than two atoms, it only consists of two types of elements.
• Examples of binary ionic compounds include Sodium Chloride, Magnesium Oxide, Lithium Oxide, etc.

Further Study

• Explore formulas involving transitional metals.
• Investigate formulas for compounds with polyatomic ions.
• Continue learning about naming ionic compounds.