The charge/size ratio of a cation determines its polarizing power. Which one of the following sequences represents the increasing order of the polarizing power of the cationic species, K^{+},Ca^{2+},Mg^{2+},Be^{2+}

  • Option 1)

    Ca^{2+}< Mg^{2+}< Be^{+}< K^{+}

  • Option 2)

    Mg^{2+}< Be^{2+}< K^{+}<Ca^{2+}

  • Option 3)

    Be^{2+}< K^{+}<Ca^{2+}< Mg^{2+}

  • Option 4)

    K^{+}<Ca^{2+}< Mg^{2+}<Be^{2+}

 

Answers (2)

As we learnt in

Fajans Rules -

It accounts  for the covalent character in ionic compounds covalency is favoured by

1.  Small cation

2.  Large anion and 

3.  Large charge on either ion 

-

 

 

 

 

High charge and small size of the cations increases polarisation.

As the size of given cations decreases, polarisation power of cation increases. In order of polarisation power is

K^{+}< Ca^{2+}< Mg^{2+}< Be^{2+}

 


Option 1)

Ca^{2+}< Mg^{2+}< Be^{+}< K^{+}

This option is incorrect

Option 2)

Mg^{2+}< Be^{2+}< K^{+}<Ca^{2+}

This option is incorrect

Option 3)

Be^{2+}< K^{+}<Ca^{2+}< Mg^{2+}

This option is incorrect

Option 4)

K^{+}<Ca^{2+}< Mg^{2+}<Be^{2+}

This option is correct

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