CBSE Class 10 Answered

A covalent bond formed between two different atoms, with different electronegativities is known as polar covalent bond.

Or

In other words,  

Polar bonding results with an unequal sharing of electrons. A polar bond is a type of covalent bond between two atoms or more in which electrons are shared unequally. Because of this, one end of the molecule has a slight, relative negative charge and the other a slight, relative positive charge.

Larger the difference in electronegativity, more polar the bond will be. Due to this, the more electronegative element attains a partial negative charge and the other element has a partial positive charge.

For example: H₂O; here hydrogen has a slight positive charge and oxygen has a slight negative charge.

In the following example, green circle is oxygen atom and blue circles are hydrogen atoms. Due to lone pair of electrons, the water molecule takes an angled shape and the difference in the electronegativities make oxygen atom partially negative.

H^δ+---- O^2δ-

Another example is of HCl.

When a Covalent bond is formed between H and Cl, it is polar in nature because Cl is more electronegative than H atom. Therefore, electron cloud is shifted towards Cl atom. As a result, a partial negative charge appears on Cl atom and, an equal positive charge on H atom.

H^δ+---- Cl^δ-