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In covalent bonding, understanding how electrons are shared between atoms is crucial. Electrons are not static; they move and form a region known as the electron cloud. This cloud represents the area where there is a high probability of finding the shared electrons. The shape and size of this electron cloud play an essential role in the chemical properties of the molecule. When two atoms form a bond, they each contribute electrons to the shared pair. However, how these electrons are distributed between the two atoms depends significantly on their relative ability to draw electrons towards themselves. Hence, electron distribution in a covalent bond is not always equal and is influenced by a property called electronegativity, which we will explore next.

Electronegativity is a measure of an atom's ability to attract and hold on to shared electrons. Each element has an assigned electronegativity value, and these values can offer insight into how atoms will behave when forming compounds.
A higher electronegativity value means that the atom has a stronger tendency to attract electrons. For instance, elements like fluorine and oxygen have high electronegativities and tend to pull shared electrons closer to themselves.
In a covalent bond, if there is a significant difference in electronegativity between the two atoms involved, the electron distribution will not be equal. The more electronegative atom will attract the shared electrons more strongly, causing the electron cloud to skew towards it. This attraction affects the bond's properties and contributes to the formation of what is known as a polar covalent bond.

When a covalent bond forms between two atoms with differing electronegativities, the electrons are not equally shared. This results in the formation of a polar covalent bond. In such bonds, the electron cloud is distorted towards the more electronegative atom.
For example, in a water molecule ( H_2O ), oxygen is more electronegative than hydrogen. This difference results in the electron cloud being drawn closer to oxygen than to hydrogen, making the molecule 'polar.'
The term 'polar' implies that the molecule has a partial negative charge near the more electronegative atom and a partial positive charge near the less electronegative atom. Polarity in bonds plays a crucial role in determining the interactions and physical properties of the molecules, such as solubility and boiling points.