The Ionic Trading Floor
Topic 2.4.3: Complex Ionic Ratios
The Problem: Magnesium wants to give away 2 electrons. But Chlorine can only accept 1. What happens? Magnesium needs to find TWO Chlorine atoms to complete the trade. This is why ionic compounds have specific ratios—it's all about balancing the electron exchange!
Formula Balancer
Choose Metal (Electron Donor)
Choose Non-Metal (Electron Acceptor)
⚡ The Electron Trading Floor ⚡
Mg
Magnesium
Has 2 electrons to give
Charge: +2
Cl
Cl
2 × Chlorine
Each needs 1 electron
Total charge: -2
IONIC FORMULA
MgCl₂
Metal atoms:1
Non-metal atoms:2
Charge Balance Verification
Positive Charges
+2
1 × (+2)
Negative Charges
-2
2 × (-1)
Net Charge
0
✓ NEUTRAL!
Classic Examples
MgCl₂
Magnesium gives:2e⁻
Each Cl needs:1e⁻
Cl atoms needed:2
(+2) + 2(-1) = 0 ✓
Na₂O
Each Na gives:1e⁻
Oxygen needs:2e⁻
Na atoms needed:2
2(+1) + (-2) = 0 ✓
Al₂O₃
Each Al gives:3e⁻
Each O needs:2e⁻
Ratio (Al:O):2:3
2(+3) + 3(-2) = 0 ✓
🎯 Key Examination Points
✅ Remember
- The formula ratio ensures net charge = zero
- Group number tells you the charge: Group II = +2, Group VII = -1
- Use the swap-and-drop method: Mg²⁺ + O²⁻ → swap charges → Mg₂O₂ → simplify → MgO
⚠️ Examiner Traps
- Don't write Mg₁Cl₂ — the "1" is always omitted
- Simplify formulas: Al₂O₆ is WRONG → correct is Al₂O₃
- In dot-and-cross diagrams, show ALL electrons in the outer shell, not just transferred ones
Sign In to Keep Going
You've reached the end of the free preview. Sign in — and upgrade to Plus or Pro — to keep going with Chemistry.
Full Access
Unlock all 320 lessons