Writing Chemical Formulas for Ionic Compounds

Overview

• Aim: Convert chemical names like Magnesium Chloride to chemical formulas (e.g., MgCl₂)
• Approach: Identify elements, determine charges, balance charges, and write formulas

Example 1: Lithium Oxide

• Step 1: Identify Elements
  • Find Lithium (Li) and Oxygen (O) on a simplified periodic table
  • Note: Oxide is Oxygen with a charge
• Step 2: Determine Charges
  • Lithium is in the +1 charge column (Li⁺)
  • Oxygen is in the -2 charge column (O²⁻)
• Step 3: Balance Charges
  • One Li⁺ and one O²⁻ do not balance
  • Add another Li⁺ to balance: 2 Li⁺ and 1 O²⁻
• Step 4: Write Chemical Formula
  • Li₂O (2 Lithium, 1 Oxygen)

Definitions

• Ionic Compounds: Composed of metals and nonmetals
• Charges: Metals have positive charges, nonmetals have negative charges

Example 2: Potassium Nitride

• Step 1: Identify Elements
  • Potassium (K) and Nitrogen (N)
• Step 2: Determine Charges
  • Potassium is in +1 charge column (K⁺)
  • Nitrogen is in -3 charge column (N³⁻)
• Step 3: Balance Charges
  • Add more Potassium: 3 K⁺ balance 1 N³⁻
• Step 4: Write Chemical Formula
  • K₃N (3 Potassium, 1 Nitrogen)

Example 3: Sodium Chloride (Table Salt)

• Step 1: Identify Elements
  • Sodium (Na) and Chlorine (Cl)
• Step 2: Determine Charges
  • Sodium is in +1 charge column (Na⁺)
  • Chlorine is in -1 charge column (Cl⁻)
• Step 3: Balance Charges
  • One Na⁺ balances one Cl⁻
• Step 4: Write Chemical Formula
  • NaCl (1 Sodium, 1 Chlorine)

Example 4: Aluminum Oxide

• Step 1: Identify Elements
  • Aluminum (Al) and Oxygen (O)
• Step 2: Determine Charges
  • Aluminum is in +3 charge column (Al³⁺)
  • Oxygen is in -2 charge column (O²⁻)
• Step 3: Balance Charges
  • Add more Aluminum and Oxygen: 2 Al³⁺ (total +6) and 3 O²⁻ (total -6)
• Step 4: Write Chemical Formula
  • Al₂O₃ (2 Aluminum, 3 Oxygen)

Common Mistakes

• Mistake 1: Writing a number 1 after an element (e.g., LiO₁ instead of Li₂O)
• Mistake 2: Including charges in the chemical formula (e.g., Li⁺₂O²⁻ instead of Li₂O)

Additional Resources

• For further practice, explore writing formulas for compounds with transition metals and polyatomic ions.