What is electronegativity?

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. For example, fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegative at 0.7. The shared electron pair can be shared equally (nonpolar bond) or unequally (polar bond).