Electronegativity: A qualitative measure of the ability of an atom in a chemical compound to attract shared electrons to itself is called electro negativity. It is the property of an atom which increases with its tendency to attract the electrons of a bond.
Example: F, Cl, Br, S, O etc.​
Moving from left to right in any period, the electronegativity increases.
Moving from top to bottom in any group, the electronegativity decreases.