The s-Block Elements (Group 1 and Group 2)
1. Introduction to s-Block Elements
The elements in which the last electron enters the s-orbital of the outermost shell
are called s-block elements.
The s-block consists of:
- Group 1 – Alkali Metals
- Group 2 – Alkaline Earth Metals
2. General Electronic Configuration
Group 1: $[Noble\ Gas]\,ns^1$
Group 2: $[Noble\ Gas]\,ns^2$
Group 2: $[Noble\ Gas]\,ns^2$
3. Group 1 – Alkali Metals
Group 1 elements include:
- Li, Na, K, Rb, Cs, Fr
4. Physical Properties of Alkali Metals
- Soft metals (can be cut with knife)
- Low density
- Low melting and boiling points
- Good conductors of heat and electricity
5. Chemical Properties of Alkali Metals
(a) Reaction with Oxygen
$4Li + O_2 \rightarrow 2Li_2O$
$2Na + O_2 \rightarrow Na_2O_2$
$K + O_2 \rightarrow KO_2$
$2Na + O_2 \rightarrow Na_2O_2$
$K + O_2 \rightarrow KO_2$
(b) Reaction with Water
$2Na + 2H_2O \rightarrow 2NaOH + H_2 \uparrow$
Reactivity increases down the group.
6. Oxidation State and Reducing Nature
Alkali metals show only +1 oxidation state.
They are strong reducing agents.
7. Important Compounds of Sodium
(a) Sodium Carbonate – Washing Soda
$Na_2CO_3 \cdot 10H_2O$
(b) Sodium Bicarbonate – Baking Soda
$NaHCO_3$
8. Biological Importance of Sodium and Potassium
- Sodium – nerve impulse transmission
- Potassium – muscle contraction
9. Group 2 – Alkaline Earth Metals
Group 2 elements include:
- Be, Mg, Ca, Sr, Ba, Ra
10. Physical Properties of Group 2 Elements
- Harder than alkali metals
- Higher melting points
- Denser than Group 1 elements
11. Chemical Properties of Group 2 Elements
Reaction with Water
$Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2$
Be does not react with water due to oxide layer.
12. Oxidation State of Group 2 Elements
Group 2 elements show +2 oxidation state.
13. Anomalous Behaviour of Beryllium
Beryllium differs from rest due to:
- Small size
- High ionization energy
- High electronegativity
14. Important Compounds of Calcium
(a) Calcium Oxide (Quick Lime)
$CaCO_3 \xrightarrow{\Delta} CaO + CO_2$
(b) Calcium Hydroxide (Slaked Lime)
$CaO + H_2O \rightarrow Ca(OH)_2$
15. Hardness of Water
Hardness is caused by presence of:
- $Ca^{2+}$ ions
- $Mg^{2+}$ ions
16. Comparison Between Group 1 and Group 2
| Property | Group 1 | Group 2 |
|---|---|---|
| Valency | 1 | 2 |
| Reactivity | Very high | Moderate |
| Oxidation State | +1 | +2 |
17. Flame Test
- Sodium – Golden yellow
- Potassium – Lilac
- Calcium – Brick red
- Barium – Apple green
18. Diagonal Relationship
Lithium shows diagonal relationship with Magnesium.
19. Uses of s-Block Elements
- Na – street lights
- Mg – fireworks
- Ca – cement
20. JEE Important Points
- Trends down the group are very important
- Anomalous behavior is frequently asked
- Reactions with oxygen and water are high-weightage