S-Block Element (Reaction)

S-Block Element (Reaction)-

Notes-

Chemical properties of Alkali metal-

 Flame Coloration

    Li- Carmine

    Na- Golden yellow 

    K- Violet

    Rb- Red violet

    Cs-Blueish

 

Chemical Reactivity-

     Due to strong electro-positive character Alkali metal show high reactivity. The reactivity is due to following three character.

   1. Low Ionization energy.

   2. Low heat of atomization.

   3. High heat of Hydration energy. 

Low Ionization Energy-

 

     M(g) ➝ M⁺(g)

^{Low Heat of atomization}

          M(s)➝M(g)

High Heat of Hydration 

 M⁺(g)+H₂O➝  M⁺(aq)

In gaseous state-

 

Li<Na<K<Rb<Cs

In aqueous state-

Rb>K>Na ,    Cs<Li⁺(aq)

Reaction with oxygen-

Alkali metal form different type of oxide on Reaction with Oxygen

Li➝ Oxide ➝Li₂O

Na➝peroxide ➝ Na₂O₂

k, Rb, Cs➝ MO₂

* These metal when present in liquid NH₃ on reaction with Oxygen formed normal state.

* When we dissolve alkali metal in water the nature of the solution is basic

Reaction with water-

These metal on reaction with water librate hydrogen gas forming metal hydroxide.

M + H₂O(l)NH₃  MOH +H₂

* This reaction is high exothermic in nature.

* The metal react vigorously with water.

Li < Na < K < Rb < Cs

Note- All of group 1 element Lithium(Li), Sodium(Na), Potassium(k), Rubidium(Rb), Cesium(Cs) react vigorously or even explosively with cold water. In case the aqueous metal hydroxide and hydrogen gas are produce.

Reactivity-

 Li < Na < K < Rb < Cs

* Due to high  exothermic in nature Alkali metal are kept in Kerosene.

* Li are stored in paraffin waxed and Li are not stored in kerosene oil . Due to its low density.

LiOH, NaOH, KOH, RbOH, CsOH  

LiOH< NaOH< KOH< RbOH< CsOH  

Solubility in liquid Ammonia (NH₃)

All Alkali metal are soluble in liquid ammonia giving a deep blue color.

The blue color of the Solution is due to solvated ammoniated  electron 

When light is incident these Solvated electron can excite to higher energy level absorbing red color. When they fall back they emit blue color in the visible ray.

Na + NH₃(l)➝Na⁺(l)NH₃ + e⁻

 e⁻ + хNH₃ ➝ e(NH₃)x

e(NH₃)x- Solvated ammoniated

Na⁺ + e(NH₃)x ➝ Na[e(NH₃)x⁺]

Extraction of Mg and Ca