Group 2 Elements Revision Notes, Mnemonics and Trends

Group 2 Elements (Alkaline Earth Metals): Be, Mg, Ca, Sr, Ba, Ra

This quick revision Notes, Trends and Mnemonics are very important for CSIR-NET, GATE, SLET, NEET, JEE Main/Advanced, IIT-JAM.

Mnemonics: Be: Be | Mg: Magician | Ca: Can | Sr: Strong | Ba: Banana | Ra: Raita

1. General Electronic Configuration

ns² (two valence electrons → divalent, less reactive than Group 1)

2. Key Periodic Trends (Down the Group: Be → Ra)

Property	Trend	Exception/Important Note
Atomic & Ionic Radius	Increases	Be < Mg < Ca < Sr < Ba < Ra
Ionisation Energy	Decreases	Be > Mg > Ca > Sr > Ba > Ra Be has highest IE in group
Electronegativity	Decreases	Be (1.5) > Mg (1.2) > Ca ≈ Sr ≈ Ba
Electropositive Character	Increases	Be < Mg < Ca < Sr < Ba
Melting & Boiling Point	Decreases (generally)	Be > Mg > Ca > Sr > Ba (Stronger metallic bonding than Group 1)
Density	Increases	Be < Mg < Ca < Sr < Ba
Hydration Energy	Decreases	Be²⁺ > Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ (Higher charge density in smaller ions)
Flame Colour	—	Ca (brick red), Sr (crimson red), Ba (apple green), Mg & Be (no colour)
Reactivity	Increases	Be < Mg < Ca < Sr < Ba

3. Anomalous Behaviour of Beryllium

• Small size, high IE, high electronegativity, high polarising power (Fajans' rule)
• Compounds are predominantly covalent (amphoteric oxide/hydroxide)
• Does not react with water even at red heat
• Forms carbide Be₂C (methanide, gives CH₄ on hydrolysis)
• Diagonal relationship with Al (similar charge/radius ratio)
• BeCl₂ polymeric in solid, linear in vapour

4. Important Compounds & Reactions

• Oxides & Hydroxides:
  • BeO (covalent, amphoteric), MgO (ionic, basic)
  • CaO, SrO, BaO (strongly basic)
  • Solubility of hydroxides: Be(OH)₂ < Mg(OH)₂ < Ca(OH)₂ < Sr(OH)₂ < Ba(OH)₂
  • Thermal stability of carbonates: BeCO₃ < MgCO₃ < CaCO₃ < SrCO₃ < BaCO₃
• Carbonates & Bicarbonates:
  • All normal except BeCO₃ (unstable)
  • MgCO₃ (magnesite), CaCO₃ (limestone)
• Sulphates:
  • Solubility decreases: BeSO₄ > MgSO₄ > CaSO₄ > SrSO₄ > BaSO₄ (almost insoluble)
  • Thermal stability increases down the group
• Nitrates: All decompose to oxide + NO₂ + O₂
• Halides: BeX₂ covalent & polymeric; others ionic
• Reactions:
  • With water: Mg (slow/steam), Ca-Sr-Ba (cold water)
  • With O₂: All form MO (BeO amphoteric)

5. Exam Tricks & Mnemonics

Flame Test Colours:
Ca (Brick red), Sr (Crimson red), Ba (Apple green)
Mnemonic: Carmine Sreet Banana → Colours: Red, Crimson, Green.

Solubility Order of Hydroxides: Increases down group
Sulphates: Decreases down group
Remember: “Be Mg Ca Sr Ba – Hydroxides go up, Sulphates go down”.

Diagonal Relationship Be-Al:
Both amphoteric oxides, covalent chlorides, form carbide giving CH₄, similar hydration energy.

Thermal Stability Carbonates: BeCO₃ least stable → decomposes easily.

Hardness: Be & Mg compounds impart hardness to water (temporary for bicarbonates, permanent for sulphates).

Strongest Reducing Agent: Ba (in group), but Li (overall in s-block due to hydration).

6. Frequently Asked Exam Questions

• Why is beryllium anomalous?
• Order of solubility of sulphates/hydroxides/carbonates?
• Why Be compounds are covalent?
• Diagonal relationship of Be with Al?
• Flame colours and reason?
• Why Mg does not react with cold water readily?
• Which carbonate is most stable? (BaCO₃)
• Why BaSO₄ is used in barium meal?

7. Quick Revision One-Liners

• Beryllium: covalent, amphoteric, hardest, no flame colour.
• Magnesium: milk of magnesia (Mg(OH)₂), chlorophyll, Epsom salt (MgSO₄·7H₂O).
• Calcium: gypsum (CaSO₄·2H₂O), plaster of Paris (CaSO₄·½H₂O), lime (CaO).
• Strontium: used in fireworks (red flame).
• Barium: BaSO₄ in X-ray imaging (insoluble, high density).
• Radium: radioactive, used earlier in luminous paints.
• All stored under oil (except Be, inert).