S-BLOCK ANALYSIS:

THE ALKALI METAL:

Physical properties: General electronic configuration is ns^1.

^{General Oxidation State is : +1}

^{ATOMIC /IONIC SIZE : Li<Na<K<Rb<CS}

^{DENSITY: Li<Na<K<Rb<Cs}

IONISATION ENERGY: Li>Na>K>Rb>Cs

Flame Colour:

Li	Na	K	Rb	Cs
Crimson Red	Golden Yellow	Violet	Reddish Violet	Blue

Reducing Property (Molten state) : Li<Na<K<Rb<Cs

(Aquous) : Li>K=Rb>Cs>Na

Also Basic Nature increases Down the Group.

CHEMICAL PROPERTIES:

Reaction with O₂

Lithium form Normal oxide :Li₂O

Sodium Form Peroxide :Na₂O₂

Potassium, Rubidium, Cessium form Super Oxide : .MO2

Li₂O + H₂O → 2LiOH
2Na₂O₂ + 2H₂O → 4NaOH + O₂
2KO2 + 2H2O → 2KOH + H2O2 + O2 ( same for Rb and Cs)

Reaction With Water:
M2O + 2HX → 2MX + H2O                
MOH + HX → MX + H2O               
M2CO3 + 2HX → 2MX + CO2 + H2O (M = Li, Na, K, Rb or Cs)
(X = F, Cl, Br or I)
WITH AMMONIA :
Alkali metals dissolve in liquid ammonia or other donor solvents like aliphatic amines or hexamethylphosphoramide to give blue solutions. These solutions are believed to contain free electrons
Na + xNH₃ → Na⁺ + e(NH₃)_x⁻
^{Reaction with nitrogen:
Lithium is the only metal that combines directly with nitrogen at room temperature.}
^{3Li + 1/3N₂ → Li₃N}
^{Li₃N can react with water to liberate Ammonia.
Li₃N + 3H₂O → 3LiOH + NH₃
Reaction with hydrogen:
With hydrogen, alkali metals form saline Hydrides that Hydrolyse in water.
Na + H₂ → NaH (at high temperatures)
NaH + H₂O → NaOH + H₂
Reaction with carbon:
Lithium is the only metal that reacts directly with carbon to give dilithium acetylide. Na and K can react with acetylene to give acetylides.
2Li + 2C → Li₂C₂
Na + C₂H₂ → NaC₂H + 1/2H₂ (at 150⁰C)
Na + NaC₂H → Na₂C₂ (at 220⁰C)}
 SOME VERY IMPORTANT POINT TO REMEMBER:   
Small cation and large anion favours covalency.
Order: LiCl > NaCl > KCl > RbCl > CsCl & . LiI > LiBr > LiCl > LiF..
Higher  the charge on the cation higher will be its polarizing power and hence larger is the covalent character: Na⁺CI^- < Mg⁺²CI2 < AI⁺³ CI3  ..             
Higher the charge on the anion, more easily it gets polarized thereby imparting more covalent character to the compound formed  for example covalent character increase in the order. NaCI < Na2SO4 < Na3PO4 .
 Lattice Energies: IT Is the amount of energy required to separate one mole of solid ionic compound into its gaseous ions. 
More the lattice energy, higher is the melting point of the alkali metals halide and lower is its solubility in water
 Hydration Energy:  It is the amount of energy released when one mole of gaseous ions combine with water to form hydrated ions.
M⁺ (g) + aq → M⁺ (aq) + hydration energy .
X^- (g) + aq → X^- (aq) + hydration energy .    
Higher the hydration energy of the ions greater is the solubility of the compound in water.
The solubility of the most of alkali metal halides except those of fluorides decreases on descending the group since the decrease in hydration energy is more than the corresponding decrease in the lattice energy.
Due to high hydration energy of Li⁺ ion, Lithium halides are soluble in water except LiF which is sparingly soluble due to its high lattice energy.
For the same alkali metal the melting point decreases in the order
fluoride > chloride > bromide > iodide
For the same halide ion, the melting point of lithium halides are lower than those of the corresponding sodium halides and thereafter they decrease as we move down the group from Na to Cs.
The low melting point of LiCl (887 K) as compared to NaCl is probably because LiCl is covalent in nature and NaCl is ionic.
THE SOLVAY'S PROCESS: 
Also known as Ammonia soda process , Carbon dioxide is passed through a brine solution (containing about 28 % NaCl) which is saturated with ammonia to form Sodium Carbonate.
 $2 N H_{3} + H_{2} O + C O_{2} \to (N H_{4})_{2} C O_{3}$ 
 $(N H_{4})_{2} C O_{3} + H_{2} O + C O_{2} \to 2 N H_{4} H C O_{3}$ 
 $N H_{4} H C O_{3} + N a C l \to N a H C O_{3} ↓ + N H_{4} C l$ 

The precipitate of sodium bicarbonate is filtered , dried and ignited to form sodium carbonate..
 $2 N a H C O_{3} h e a t N a_{2} C O_{3} + C O_{2} + H_{2} O.$ 

The carbon dioxide required for the reaction can be obtained by heating limestone (calcium carbonate) to 1300 K in a lime klin . Lime dissolves in water to form calcium hydroxide which is then transferred to the ammonia recovery tower.
 $C a C O_{3} h e a t C a O + C O_{2}$ .
 $C a O + H_{2} O \to C a (O H)_{2}$ .

Ammonia required for the process can be prepared by heating ammonium chloride with calcium hydroxide.
 $2 N H_{4} C l + C a (O H)_{2} 2 N H_{3} + C a C l_{2} + H_{2} O.$ 

Hence, the only byproduct of the reaction is calcium chloride.
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