POLAR COVALENT BOND: (IONICCHARACTER IN COVALENT BONDS):,

 POLAR COVALENT BOND: (IONICCHARACTER IN COVALENT BONDS):

             The relative ability of a covalently bonded atom to attract shared pair of electrons more toward itself is called electro negativity. This factor increases due to increase in effective nuclear charge and decreases progressively in larger atoms. Hence electro negativity increases from left to right across a period and it decreases down the group in a periodic table. Out of non-metals fluorine is consider to be most electronegative element and cesium metal is the least electronegative. In non metals hydrogen is the least electronegative. In some cases it is almost similar. The increasing order of electro negativity in some common non metal is gain as;    

 CL <  N <  O < F

Increasing order of electro negativity causes a greater degree of bond polarity.

POLARITY IN DIATOMIC MOLECULES:

             Molecules consisting of two identical atoms such as H₂, CL₂, N₂, O₂ and F₂ are always purely covalent. Such molecules are called non-polar molecules. In these molecules the electron pair is equally shared between the two bonded atoms. This happens because the electro negativity difference between the two atoms is zero. However, when two different atoms are joined by a covalent bond the bonding electron pair is not equally shared due to the difference of electro negativity. Such molecules are called polar molecules. In such molecules more electronegative atom attracts shared pair of electron more toward itself and create partial negative charge (s-) on more electro negative atom. On the other side positive centre of less electro negative atom does not coincide with the centre of negative charge hence equal partial positive charge (s+) is created on the other end of molecule. As a result covalent molecule become polar. The reparation of positive and negative poles within a molecules is called dipole. The existence of dipole in covalent molecules shows ionic behavior in covalent molecules. The greater the difference in electro negativity between the two atoms joined by covalent bond, the greater the percentage of ionic character. Such molecules are called predominately ionic. A zero difference shows zero ionic character and bond is purely covalent.

                      Non – polar                                                                 Polar covalent bond

            A dipole is usually represented by an arrow with a cross base. The head of the arrow points towards the negative pole (end) of polar molecule.

                        S+                                S-

                     H                                 CL

 

 

DIPOLE IN MOLECULES CONTAININGMORE THAN TWO ATOMS:

 

            In polyatomic molecules shape (geometry) of molecule decides the polarity of the molecule.            Overall dipole of the molecule is the sum of all the individual dipoles. Equal dipole pointing in opposite directions cancel each other. Hence a symmetrical distribution of polar covalent bonds produces a non polar molecule. Polar molecules tend to arrange themselves ionic electric field so that the positive end of the molecule is toward the negative charge or negative end of the molecule is turned toward the positive charge. Non polar molecules are oriented randomly in an electronic field.

DIPOLE IN MOLECULES CONTAININGMORE THAN TWO ATOMS