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Chapter: 11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes

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Applications of electronegativity

1) Nature of bond The concept of electronegativity can be used to predict whether the bond between similar or dissimilar atoms is non-polar covalent bond, polar covalent bond (or) ionic bond. 2. Percentage of ionic character in a polar covalent bond

Applications of electronegativity

1) Nature of bond

The concept of electronegativity can be used to predict whether the bond between similar or dissimilar atoms is non-polar covalent bond, polar covalent bond (or) ionic bond.

1.           When XA = XB, i.e. XA- XB = 0, then A-B bond is non polar covalent bond or simply covalent bond and is represented as A-B. eg. H-H bond in H2 molecule is a covalent bond and is represented as H-H bond.

2.           When XA is slightly greater than XB, i.e. XA - XB is small, the A-B bond is polar covalent bond and is represented as Ad--Bd+ . e.g. The O-H bonds in H2O molecule are polar covalent bonds and are represented as Od--Hd+, since XO> XH and XO - XH is small.

3.     When XA>> XB, i.e., XA - XB is very large, A-B bond is more ionic or polar bond and is represented as A--B+, Since XA>> XB. For example Na-Cl bond in Na Cl molecule is an ionic bond and is represented as Na+Cl- (Here Cl = A and Na = B).

 

 2) Percentage of ionic character in a polar covalent bond

Pauling estimated the percentage of ionic character in various Ad--Bd+ polar covalent bonds from known (XA-XB) values and has derived the following conclusions :

1.           When (XA-XB) = 1.7, the amount of ionic character in Ad--Bd+ bond is 50% and that of covalent character is also 50%. Thus A-B bond is 50%  ionic and 50% covalent.

2.           When (XA-XB) < 1.7, the amount of ionic character in Ad--Bd+ bond is less than 50% and that of covalent character is more than 50%. Thus Ad--Bd+  bond is predominantly covalent and hence is represented as A-B.

When (XA-XB) > 1.7, the amount of ionic character in Ad--Bd+ bond is more than 50% and that of covalent character is less than 50%. Hence Ad--Bd+ bond is predominantly ionic and hence is represented as A-B+.


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