GROUP-1 AND GROUP-2 -THE CHEMICAL PROPERTIES - PART -II

 PROPERTIES OF  S-BLOCK

CHEMICAL PROPERTIES







 

ALKALI METAL

 

ALKALINE EARTH METAL

 

  •         The alkali metal are highly reactivity due to their      large size and low ionisation.

 

  •  The reactivity of these metal increases down the group.

 

  •          The alkaline earth metal are less reactivity then the alkali metal because it takes more energy to remove two valence electrons from an atom then one valence electron
  •       The reactivity of these element increases going down the group.









    1.4.2.a   REACTION WITH HALOGEN:

 

 

ALKALI METAL

 

 

2M + X2          ®       2M+X-


  

[M= Li, Na, K, Rb, Cs]   

 [X= Halogen family’s Element]          

(i.e ) F,Cl,Br I ]

 

Alkaline metal + Halogen  ➡   Ionic halides

 

  •    Increase down the group because of corresponding  decreasing in ionisation enthalpy.
  •  All metal halides are ionic crystal.
  •   But Lithium Iodide shows covalent character ,because of its high polarization capability of lithium ion. [Li ion  small in size and high tendency to distort electron cloud around the negative halide ions.]

 

 

 

ALKALINE EARTH METAL

 

 

M  +   X2                                                        

           
 

  🔺
 ⟶     MX2


              

 


[ M = Be, Mg, Ca, Sr, Ba ,Ra]

         [X = Halogen family’s Element (i.e )F, Cl ,Br I]

                                    

                                                     🔺

Alkaline Earth Metal +Halogen   ➡       Halides   



 

 

      























NOTES:

ü  The distortion of electron cloud of the anion by the cation is called polarization


1.4.2.b REACTION WITH HYDROGEN[H2 ].

        

 

ALKALI METAL

 


        ⟶        2M  +   H2                          2 M+ H-

 

[M= Li, Na, K, Rb, Cs]

 

Alkali metal + H ⟶ Ionic Hydrides

 (IONIC SALT)


  •    All alkali metal reacts with Hydrogen at 673K [ 399.85 0C].      
  • But Lithium at 1073 K [799.85 0C] to  form Ionic hydrides.
  •  Reactivity decreases with down the group.[ Li to Cs] 
  • The ionic character of hydrides increases down the group. [Li to Cs]
  • But the stability  decreases down the group [Li to Cs]
  • Hydrides behave strong in reducing agent
  •  Their reducing agent decreases down the group [Li to Cs].

 

ALKALINE EARTH METAL

 


       ⟶        2M  +   H2                          2 M+ H-

 

       [ M = Be, Mg, Ca, Sr, Ba ,Ra]

 

   Alkali metal + H  ⟶ Ionic Hydrides 


 

Ø All the alkaline earth metal except Beryllium combines with hydrogen on heating to form their hydrides with general formula MH2

 


1.4.2.c  REACTION  WITH OXYGEN [ O2]:


ALKALI METAL

 

M  + O2       


[M= Li, Na, K, Rb, Cs]        

Alkali metal + Air        ⟶       Simple oxides                                          peroxide  and super                          oxides    

                             (METAL OXIDES)     


·        All Alkali metal on exposure to air or oxygen burn vigorously, forming oxides on the surface.

·        Lithium forms only  Monoxides 

·        Sodium forms only Monoxides and Peroxides

·        Remaining elements form Monoxides, peroxides and superoxides.

 ALKALINE EARTH METAL


 

 


 

 

Alkaline Earth Metal + O   ⟶                Metal Oxide


1.4.2.d. REACTION WITH WATER [ H2O]:

  

ALKALI METAL


⟶ 2M +  2H2O                2MOH    +    H2   

[M= Li, Na, K, Rb, Cs]    

Alkali metal + Water  ⟶  Corresponding H                                         + liberation of     H                                  (METAL HYDROXIDES) 

           

  • This metal also react with alcohols, alkynes which contains active hydrogen

           ALKALINE EARTH METAL

 


M       +      H2O          →          M (OH)2


[ M = Be, Mg, Ca, Sr, Ba ,Ra]

Alkali Earth Metals +  Water   ⟶    Metal                                                          Hydroxide



1.4.2.e  REACTION  WITH  LIQUID AMMONIUM [ NH3]:


ALKALI METAL

 

M  + [x+ y]NH3     ⟶       [M(NH3)X]+                                           +      [e(NH3)y]-  

 

[M= Li, Na, K, Rb, Cs]

v Alkali metal dissolve in liquid ammonium to give deep blue solution that are in the nature.

v This happens because the alkali metal atom readily losses its valence electron in ammonium.

v Both cation and the electron are ammoniated to give ammoniated cation and ammoniated electrons.

 

      M+  +   e-                  MNH2   + H2

             

 [M= Li, Na, K, Rb, Cs]

v The blue color of the solution is due to the ammoniated electron which absorbs the energy in the visible region of light and thus imparts blue color to the solution.

v  This solution are paramagnetic and  on standing  slowly liberate hydrogen resulting in the formation of an amide.

v In concentrate solution, the blue color changes the bronze color and become diamagnetic

 

  ALKALINE EARTH                 METAL













  








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