modern periodic table
Electronegativity is the tendency of an atom to attract the shared pair of electrons in a chemical bond towards itself. In other words, it is measure of the ability of an atom in a molecule to attract electrons.
Basically, electronegativity increases from left to right across any period and from bottom to top in any group of periodic table.
When elements of different electronegativities combine, it results in ionic compound.
The electronegativity values of non-metals do not differ much.
The larger the elecronegativity difference, the more polar covalent bond will be.