Lecture Notes: Determining the Formula of Ionic Compounds

Key Concept

• Ionic Compounds: Must have an overall charge of zero.
• Charges on Ions: The charges on the ions in a compound should cancel each other out.

Examples of Ionic Compounds

1. Sodium Chloride (NaCl)

   • Sodium ion: (Na^+)
   • Chloride ion: (Cl^-)
   • Formula: (NaCl)
   • One sodium ion cancels out the charge on one chloride ion.

2. Sodium Oxide (Na₂O)

   • Sodium ion: (Na^+)
   • Oxide ion: (O^{2-})
   • Formula: (Na_2O)
   • Two sodium ions are needed to cancel out the charge on one oxide ion.

3. Magnesium Iodide (MgI₂)

   • Magnesium ion: (Mg^{2+})
   • Iodide ion: (I^-)
   • Formula: (MgI_2)
   • Two iodide ions are required to cancel the 2+ charge on the magnesium ion.

4. Lithium Carbonate (Li₂CO₃)

   • Lithium ion: (Li^+)
   • Carbonate ion: (CO_3^{2-})
   • Formula: (Li_2CO_3)
   • Two lithium ions are needed to cancel the charge on one carbonate ion.

5. Calcium Hydroxide (Ca(OH)₂)

   • Calcium ion: (Ca^{2+})
   • Hydroxide ion: (OH^-)
   • Formula: (Ca(OH)_2)
   • Two hydroxide ions are needed to cancel the charge on one calcium ion.
   • Important: Use brackets ((OH)_2) to indicate two hydroxide ions.

6. Magnesium Nitrate (Mg(NO₃)₂)

   • Magnesium ion: (Mg^{2+})
   • Nitrate ion: (NO_3^-)
   • Formula: (Mg(NO_3)_2)
   • Two nitrate ions are needed to cancel the 2+ charge on the magnesium ion.
   • Use brackets ((NO_3)_2) to show two nitrate ions.

Important Tips

• Brackets Usage: Essential when multiplying a whole ion group by a number, e.g., ((OH)_2) or ((NO_3)_2).
• Exam Preparation: Similar level difficulty questions will appear in exams; no more complex than examples shown.
• Additional Practice: Available in the revision workbook (link provided in the lecture).

Conclusion

• By mastering the balance of ion charges, one can determine the formula of any ionic compound.
• Practice with exam-style questions to solidify understanding.<|vq_13348|>