CHEMICAL BONDING - COVALENT BOND PART-2

 COVALENT BOND:


INTRODUCTION:

    • Langmuir (1919) refined the Lewis postulation by abandoning the idea of the stationary cubical arrangement of the octet and by introducing the term covalent bond.
    •   The Covalent bond is also known as ELECTRON-PAIR BOND. 
    •  The attractive force between atoms created by sharing of an electron-pair.
    • The compound containing a covalent bond are called COVALENT  COMPOUND

CONDITION FOR FORMATION OF COVALENT BOND:



a.NUMBER OF VALENCE ELECTRON:

  (i.e).  Each of the atoms A and B should have 5,6, or 7 valence electrons so that both achieve the stable octet easily by sharing 3,2 or 1 electron.


 

b. EQUAL ELECTRONEGATIVITY:

The atom A will not transfer electrons to B if both have equal electronegativity, and hence electron sharing will take place. This can be strictly possible only if both the atoms are of the same elements.



 

c. EQUAL SHARING OF ELECTRON:

           The atom A and B should have equal (nearly equal) electron affinity so that they attract the bonding electron pair equally. Thus equal sharing of electrons will form a non-polar covalent bond. Of course, precisely equal sharing of element have exactly the same electron affinity



 CHARECTERISTIC OF COVALENT COMPOUND:

  

  •       The atom in a covalent molecule are firmly held by the shared electron pair, the individual molecules are attracted to each other by weak VAN DER WAAL FORCE. 
  •  The molecules can be separated easily as not required much energy to overcome the inter molecules attraction. The general properties of Covalent compound are


i) Gaseous, Liquid or Solid at room temperature:

    Due to weak inter molecular force between molecules, the covalent compound goes under ordinary condition when the are in any of three states (gas, liquid or solid). 



   Low melting point and boiling points:

      •    These compounds have low boiling point or melting point 
      • The molecules held together in the solid crystal lattice by weak force.
      •  As if we heat that crystal, it will convert into liquid rapidly and acquire kinetic energy for  free movements as in a liquid.
      •  Because the movement it can also easily converted from liquid to gas.

 

Neither hard nor brittle:

      • This compound is neither harder nor brittle then ionic compound.
      •  Here weak force holding the crystal lattice and there are no force of repulsion like ionic compound.

  

 

Soluble in organic solvent:

      • Generally it dissolve in nonpolar  organic solvent(benzene, ether etc..). 
      • The kinetic energy of the solvent molecules easily overcome the weak inter molecular forces
      • And these compound are insoluble in water. But very few compound are soluble in water because Hydrogen- bonding.

 

  

    Non-Conductors of electricity; 

      •    In covalent molecules there is absence of charge(“+” or  “-“).
      •    So it unable to conduct electricity in molten or solution state.


Exhibits Isomerism

      •   These compounds are rigid and directional.
      •  Hence the atom are held together by the shared electron pair and not by electrical lines of force.
      • This affords opportunity for various spatial arrangement and covalent compound exhibit stereoisomerism

  


Molecular Reaction:

      •  The molecules reactions are very slow because there is no electrical force which can speed up the reaction.
      •     Thus the reaction goes under whole changes




 















 



DDSS

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