Quick Summary
Groups 1 and 2 contain the most reactive metals. Their chemistry is dominated by strong reducing power, ionic compound formation, and important industrial compounds. NEET carries 1–2 questions from this chapter; board exams test industrial preparations of NaOH, Na₂CO₃, and lime compounds.
Key Concepts and Definitions
- Alkali metals (Group 1): Li, Na, K, Rb, Cs, Fr — ns¹ configuration
- Alkaline earth metals (Group 2): Be, Mg, Ca, Sr, Ba, Ra — ns² configuration
- Diagonal relationship: Li resembles Mg; Be resembles Al in properties
- Flame colours: Li (crimson), Na (yellow), K (violet), Ca (brick red), Sr (scarlet), Ba (apple green)
- Plaster of paris: CaSO₄ · ½H₂O — sets hard by absorbing water
- Portland cement: Mixture of CaO, SiO₂, Al₂O₃, Fe₂O₃
Physical Properties Comparison
| Property | Alkali Metals (Gp 1) | Alkaline Earth (Gp 2) |
|---|---|---|
| Valence electrons | 1 (ns¹) | 2 (ns²) |
| IE | Low (lowest in period) | Slightly higher than Gp 1 |
| Hardness | Very soft (cut with knife) | Harder than Gp 1 |
| Melting point | Low | Higher than Gp 1 |
| Reactivity | Very high | High (less than Gp 1) |
| Density | Li, Na, K float on water | Generally denser |
Important Compounds of Sodium
NaOH (Caustic soda):
- Made by: Chlor-alkali process — electrolysis of brine (NaCl solution)
- 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
- Used in soap making, paper industry, petroleum refining
Na₂CO₃ (Washing soda):
- Made by: Solvay process
- NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ → Na₂CO₃ (on heating)
- Used in glass making, cleaning agent, water softening
NaHCO₃ (Baking soda): Intermediate in Solvay process; used in baking, fire extinguishers
Important Compounds of Calcium
CaO (Quicklime): CaCO₃ → CaO + CO₂ (thermal decomposition of limestone) Ca(OH)₂ (Slaked lime): CaO + H₂O → Ca(OH)₂; used in mortar, whitewash CaCO₃ (Limestone): Building material; makes cement CaSO₄ · ½H₂O (Plaster of Paris): Sets to 2CaSO₄ · 2H₂O (gypsum) on adding water
Important Questions
One Mark (5)
- What is the flame colour of sodium?
- Name the process for industrial manufacture of NaOH.
- Write the formula of plaster of paris.
- Why is NaHCO₃ used in fire extinguishers?
- Which alkali metal has the highest ionisation energy?
Short Answer 3-mark (3)
- Explain why Li shows anomalous behaviour among alkali metals.
- Describe the chlor-alkali process with a balanced equation.
- What is the diagonal relationship? Give one example.
Long Answer 5-mark (2)
- Describe the Solvay process for the manufacture of sodium carbonate with equations. State its advantages.
- Compare the properties of alkali metals and alkaline earth metals (any five points).
Common Mistakes
- Writing Na₂CO₃ as a product of chlor-alkali process — it produces NaOH.
- Confusing quicklime (CaO) with slaked lime (Ca(OH)₂).
- Thinking all Group 1 metals react the same — Li is anomalous.
- Wrong flame colours: Na = yellow (not orange), K = violet (not purple).
Board Exam Tips
- Solvay process and chlor-alkali process are guaranteed 5-mark questions.
- Flame colours table appears as objective/1-mark questions every year.
- Diagonal relationships (Li-Mg, Be-Al) are favourite 3-mark questions.
- NEET: Focus on anomalous behaviour of Li and Be.
Revision Checklist
- [ ] Flame colours of all alkali and alkaline earth metals memorised
- [ ] Chlor-alkali process equations written
- [ ] Solvay process steps outlined
- [ ] Quicklime vs slaked lime distinction clear
- [ ] Li anomalous behaviour reasons listed (5 points)
Frequently Asked Questions
They form strongly alkaline hydroxides (e.g., NaOH, KOH) when dissolved in water, hence the name alkali metals.