GROUP-1 AND GROUP-2 OF PERIODIC TABLE- THE DAIGONAL RELATIONSHIP -PART-III

 



1.3 DIAGONAL RELATIONSHIP:

 

                                              The similarities properties between the first member of group 1 and the diagonally placed second members of group 2 is called the diagonal relationship. It is due to similar in

·        Atomic size

·        Electronic configuration

·        Physical and chemical properties

·        Etc..








1.3.a   LITHIUM AND MAGNESIUM :

 

                     The similar properties between Magnesium and beryllium are:

 

 

PROPERTIES

 

                 LITHIUM

 

            MAGNESIUM

 

ATOMIC SIZE

 

152 pm

 

160 pm

 

IONIC SIZE

 

76 pm

 

72 pm

 

 

ELECTRONEGATIVITY

 

1.0  ( Pauling scale)

 

1.2

 

 

v Both Lithium and Magnesium are harder than other elements in the respective group.

v Lithium and Magnesium react with slowly with water.

  •          2Li(s)      +      2H2O(L)          ⟶       2LiOH(aq)        +          H2(g)
  •           Mg(S)    +       2H2O(L)        ⟶        Mg(OH)2        +        3H2

 

v Their oxides and hydroxides are much less soluble and their hydroxides decomposes on heating.

v Both form a nitride by composition with nitrogen. ( Li2O,  and  MgO)    


  •          6Li(s)               +      N2(s)             ⟶              2Li3N(S)
  •                  Al2 (S)        +       N2(G)                ⟶            2AlN(S)

 

v They do not give any super oxides and form only oxides .  (Li2O  and MgO)

v The carbonates of lithium and magnesium decompose upon heating to form their respective oxides and CO2

v Lithium and Magnesium do not form bicarbonates.

vBoth LiCl and MgCl are soluble in ethanol and are deliquescent. They crystallise from aqueous solution as hydrates, [ LiCl.2H2O   and  MgCl.8H2O.




1.3.b BERYLLIUM AND ALUMINIUM:


                        The Be and Al shows the diagonally relationship between them. Some similar properties are

 

 

Properties

 

   BERYLLIUM

 

ALUMINIUM

 

Atomic radius

 

1.12  (A0)


1.18 (A0)

 

Ionic radius


0.27(0.31) (A0)


0.51 (A0) 

 

Electronegativity

 

1.6 (pauling scale)

 

1.5  (pauling scale)



®  CHLORIDE

ü Beryllium Chloride (BeCl2) forms a dimeric structure  like aluminium chloride (AlCl3)  with chloride bridges.

ü  Beryllium Chloride (BeCl2)  also form polymeric chain structure in addition to dimer.

ü Both are soluble in organic solvents and are strong Lewis acid.

®  HYDROXIDE

ü Beryllium Hydroxides [Be(OH)2]  dissolves in excess of alkali and gives beryllate ion and  [Be(OH)]2- and hydrogen as aluminium hydroxide [Al(OH)3]   which gives aluminate ions, [Al (OH)4]-.

 

®  COMPLEXES:

ü Beryllium and Aluminium ions have strong tendency to form complexes ,

                                                                  BeF42- , AlF63-

 

®  NATURE:

ü Beryllium and Aluminium Hydroxides are amphoteric in nature.

ü  

®  CARBIDES:

ü Carbides of Beryllium ( Be2C) like  Aluminnium carbides (Al4C3)  gives METHANE on hydrolysis.

 

®  ACID:

ü Both are rendered passive by nitric acid.

 

 

 

 

 





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