This lesson explores the properties, trends, reactions, and uses of s‑block elements—specifically Group 1 (alkali metals) and Group 2 (alkaline earth metals). These elements show strong periodic trends due to their similar electron configurations.

1. Core Concepts (Short Notes)

8.1 Location & Electron Configuration

• s‑Block elements occupy Groups 1 and 2 in the periodic table.

• Outer electron configuration:

  • Group 1: ns¹

  • Group 2: ns²

• Their chemical reactivity is mainly due to the ease of losing their outer electrons.

  
  

8.2 General Characteristics of Group 1 (Alkali Metals)

Examples: Li, Na, K, Rb, Cs

• Extremely reactive metals.

• Soft, can be cut with a knife.

• Low density (Li, Na, K float on water).

• Low melting and boiling points.

• Form +1 ions.

• React vigorously with water to form alkali + hydrogen gas.

  
  

8.3 General Characteristics of Group 2 (Alkaline Earth Metals)

Examples: Be, Mg, Ca, Sr, Ba

• Less reactive than Group 1, but still quite reactive.

• Harder, denser metals.

• Higher melting points.

• Form +2 ions.

• React with water to form hydroxides (Mg reacts slowly with cold water).

  
  

8.4 Reactivity Trends

• Group 1 reactivity increases down the group due to lower ionization energy.

• Group 2 also show increased reactivity down the group, but less dramatically.

  
  

8.5 Compounds of Group 1 & 2

Group 1 Compounds:

• NaOH, Na₂CO₃, NaCl, KNO₃

• Very soluble in water.

Group 2 Compounds:

• Mg(OH)₂, CaCO₃, CaSO₄

• Carbonates and sulfates often have low solubility.

  
  

8.6 Thermal Stability

• Group 2 carbonates and nitrates are more thermally stable than Group 1.

• Larger cation charge (+2) stabilizes the anion.

  
  

8.7 Flame Colors (Important for exams)

• Li → crimson red

• Na → bright yellow

• K → lilac

• Ca → brick red

• Sr → crimson

• Ba → green

2. Key Formulas & Reactions to Remember

Reactions of Group 1 with Water:

2M + 2H₂O → 2MOH + H₂ (Where M = Li, Na, K…)

Reactions of Group 2 with Water:

M + 2H₂O → M(OH)₂ + H₂ (Mg reacts slowly; Ca, Sr, Ba react more vigorously)

Thermal Decomposition:

• Group 1 nitrates → nitrites + O₂

• Group 2 nitrates → oxides + NO₂ + O₂

Solubility Trends:

• Group 1 hydroxides & carbonates: Highly soluble.

• Group 2 hydroxides: Solubility increases down the group.

• Group 2 sulfates: Solubility decreases down the group.

3. Tips & Tricks for Exams

• Group 1 metals must be stored in oil to prevent reaction with air/water.

• Identify unknown compounds using flame tests.

• Remember: Group 2 carbonates decompose more easily than Group 1.

• Down the group: melting points generally decrease (Group 1) or slightly decrease (Group 2).

• Do not confuse solubility trends between hydroxides and sulfates.

• For reactivity trends, always link to ionization energy.

4. Important Points to Remember

• Group 1 and 2 elements lose electrons easily → form positive ions.

• Group 1 metals are more reactive than Group 2.

• Solubility patterns of hydroxides and sulfates are frequently tested.

• Flame tests are a quick way to identify metal ions.

Increasing atomic radius and decreasing ionization energy down the group explain the reactivity pattern.