S-Block Element(Alkali metal)

Notes-

Chapter-3 S-Block Element

First group and Second group element in collectively form known as S block element.

1.First group element known as Alkali metal
2.Second group element known as alkaline earth metal

Alkali Metal
Li, Na, K, Cs, Fr

Physical properties of Alkali Metal(A.M.)

1. Atomic and ionic radii has increases on moving down the group.

2. Ionization energy- They have low value of ionization energy due to greater size in period.

3. I.E. will decreases on moving down the group.

   I.E₁→ low                I.E₂→high

4.Metallic character-These are strong electro-positive metal and the metallic character is increases on moving down the group.

5. Physical state-These all are soft with Silvery white appearance and have BCC (body-centered cubic) structure normal temperature with co-ordination number is equal to the 8.

6.Melting and Boiling point- They have low M.P. and B.P. Due to weak metallic bonging.

M.P. and B.P. decreases on moving down the group due to further weakening  of metallic bonding size increases.

7. Enthalpy or Heat of atomization- 

The amount  of energy required to convert 1 mole of metal atom into gaseous atom is Enthalpy of atomization and it decreases on moving down the group due to decreases in metallic bonding,

8. Density- Alkali metal have low density due to larger atomic volume it increases on moving down the groupp.
  
    *Exception- Density of sodium is greater then potassium i.e. Na>K .

9. Photoelectric effect- Except Lithium they are all photosensitive metal
    
             Photoelectric ∝ 1/Ionization Enthalpy 
  * Photoelectric effect increases on moving down the group.

Hydration of M⁺ ions-



M^{+ (g) + H₂0(l)⟶}M^+(aq)⟶Hydrated ions

Stability  of M^+(aq) ∝H.E.H.E.

         H.E.∝ charge / size

*On moving down the group  Hydration energy will decreases.