CHEMICAL BONDING - IONIC BOND PART-1

 2.CHEMICAL BONDING


  • The interatomic attractive forces which hold the constituent (atom/ ions) together in a molecules are called chemical bonds
  • The interatomic attractive forces which hold the constituent (atom/ ions) together in a molecules are called chemical bonds.
  • The chemical bonding can be classified on the nature of the interaction between the bond.
  • And it is mainly classified into two types
                                      a. Ionic Bond – (Metal + Non- Metal)

                                      b. Covalent Bond – (Compound of non-metal)


    
    2.1. INTRODUCTION:

  • A logical explanation for chemical bonding was proved by KOSSEL and LEWIS in 1916.
  • They approach to chemical bonding based on the inertness of the noble gas, which has little or no tendency to combine with other element
  •   Element then the noble gas try to attain the completely filled electronic configuration by losing, gaining or sharing one or more electrons from outer shell.  

                     
2.2.LEWIS DOT STRUCTURE:

     Lewis introduced a simple scheme to represent the chemical bond and electron present in the outer shell of an atom called LEWIS DOT STRUCTURE.

     As per their theory (Representing the dot structure):
  •   In this scheme, the valence electrons (outer electron) of an     element represent as small dot around the symbol .  
  •    The first four dot of valence are denoted a single dot around the symbol. 

 



      • And then fifth onwards the electron are denoted as pairs.  


    


    

2.3. OCTET RULE:

                          The atoms transfer or share electrons, so that all atoms involved in chemical bonding for obtaining 8 electron in their outer most shell (valence shell).

   HELIUM :   Only helium is exception which has only two electron in valence shell and it is represented in pair  of dot.  


2.4. IONIC BOND:  

                 2.4.a. INTRODUCTION: 

                                          From KOSSEL and LEWIS treatment of the formation of an ionic bond, it follows that the formation of ionic compound would primarily depend upon.

  • The ease of formation of the positive and negative ions from the respectively neutral atoms.
  • The arrangement of the positive and negative ions in the solids, that is the lattice of the crystalline compound.  


2.4.b. FORMATION OF INONIC COMPOUND:

        The ionic bond will be formed more easily between elements with comparatively low ionization enthalpies and element with comparatively high negative value of electron gain enthalpy.

Both cation and anion ions are held together by the electrostatic attraction force which is known as ionic bond.

  • Ionic compound in the crystalline state consist of orderly three-dimensional arrangement of cations and anion held together by coulombic interaction energies.
  • These compounds crystalline in different crystal structures determines by the size of ions, their packing arrangement and other factors.
  • In ionic solid, the sum of the electron gain enthalpy and the ionization enthalpy may be positive but still the crystal structures gets stabilized due to the energy release in the formation of the crystal lattice.
Qualitative measure of the stability of an ionic compound is provided by its enthalpy of lattice formation and not simply by achieving octet of electrons around the ionic species in gaseous state.



 

POSITIVE IONS 

(CATION) 

 

NEGATIVE IONS 

(ANION)  

 

·        Involves in formation of    IONIZATION

 

·        Involves in electron gain enthalpy 

 

·        Removal of electron from neutral atom 

 

·        Additional of electron from neutral atom 

 

·        Only involves in endothermic process only 

 

·        May Involves in both endothermic or exothermic process

 

·        Most of element are metallic  

 

·        Most of elements are non-metallic 







2.4.c.PROPERTIES / CHARECTERISTIC OF IONIC COMPOUND:


   There are many significant properties of ionic bond. Some of the valuable properties are...

 a) PHYSICAL STATE: 

  •    The ionic compound form crystals rather then amorphous.   

  • They are harder and brittle solid due to the strong electrostatic force of attraction 

b) ISOMORPHISM: 

  •  Ionic compound are isomorphism (corresponding or similar in form and relations but may be different in chemical properties)
  •      They have same number of electron (similar configuration of cation and anion) with same crystal structure.






 c .MELTING AND BOILDING POINT:

  • Ionic compound have high melting and boiling point due to strong electrostatic force of attraction oppositely charged ions.

  • They have higher enthalpies of fusion and vaporization than molecular compound



d. CONDUCTIVITY:

               Depend upon an ionic mobility

      •  In solid state - no free electron, so bad conductor.
      •  In fused state or aqueous solution – free electrons, so it is good conductor. 

Conductivity order:   Solid state> Fused state >  Aqueous State               


      e. REACTIVITY:  

  • Ionic compound undergoes ionic reaction which have very high reaction rates. 

  • They do not exhibit isomerism due to non-directional nature of the polar bonds present in their compound

 

  f. SOLUBILITY: 

      •  Higher soluble in water (polar solvent) with high value of dielectric constant but insoluble in non-polar solvent due to low dielectric constant.
      •  The solubility of ionic compound decrease with increase in covalent character of ionic compound.

      • The solubility is governed by  
          • Lattice Energy:
  Larger the lattice energy the lesser is the solubility.

          • Lattice energy refers to the energy which is released while two oppositely charged gaseous ions attract to each other and form an ionic solid.
          • Lattice energy is a measure of the strength of the ionic bonds in an ionic compound.


   g. HEAT OF HYDRATION:

Larger the heat of hydration, the more is the solubility of ionic compound.

        • Heat of hydration is defined as the amount of energy released when one mole of ions undergo hydration.
        •   It is a special type of dissolution energy where in the solvent is water .   

 NOTE:

  •  Isomorphs are quite distinct from isomers as they can exist in two or more different compounds while isomers are the same compounds. 

  • Isomorphs have similar structure but isomers have dissimilar structure.








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