Writing Chemical Formulas for Ionic Compounds

Overview

• Use chemical names to formulate chemical formulas (e.g., Magnesium Chloride → MgCl2).
• Focus on identifying elements on the periodic table and balancing charges.

Key Process

Example: Lithium Oxide

1. Identify Elements

   • Lithium (Li) and Oxygen (O).
   • Lithium (Li) is a metal, and Oxygen (O) is a non-metal.
   • The periodic table's staircase separates metals from non-metals.

2. Determine Charges

   • Lithium is in the column with a 1+ charge: Li1+.
   • Oxygen is in the column with a 2- charge: O2-.

3. Balance Charges

   • Add lithium atoms to balance with oxygen.
   • Two lithium atoms are needed to balance one oxygen atom.
   • Write formula: Li₂O.

Example: Potassium Nitride

1. Identify Elements

   • Potassium (K) and Nitrogen (N).

2. Determine Charges

   • Potassium has a 1+ charge: K+.
   • Nitrogen has a 3- charge: N3-.

3. Balance Charges

   • Add three potassium atoms for one nitrogen atom.
   • Write formula: K₃N.

Example: Sodium Chloride (Table Salt)

1. Identify Elements

   • Sodium (Na) and Chlorine (Cl).

2. Determine Charges

   • Sodium has a 1+ charge: Na+.
   • Chlorine has a 1- charge: Cl-.

3. Balance Charges

   • Already balanced with one atom each.
   • Write formula: NaCl.

Example: Aluminum Oxide

1. Identify Elements

   • Aluminum (Al) and Oxygen (O).

2. Determine Charges

   • Aluminum has a 3+ charge: Al3+.
   • Oxygen has a 2- charge: O2-.

3. Balance Charges

   • Two aluminum and three oxygen atoms.
   • Write formula: Al₂O₃.

Common Mistakes

• Avoid Writing "1" in Formula: Instead of Li₂O₁, write Li₂O.
• Remove Charges in Final Formula: Do not include charges in the chemical formula (e.g., Li₂O²⁻ is incorrect).

Tips

• Use the periodic table to determine charge based on the element's column.
• Ensure ionic compounds always consist of metals and non-metals.