2.4b: recall that ionic and covalent bonding are the extremes of a continuum of bonding type and explain this in terms of electronegativity differences leading to bond polarity in bonds and molecules, and to ionic bonding if the electronegativity is large enough

The greater the difference between electronegativities, the greater the ionic character of the bond

The greater the similarity in electronegativities, the greater the covalent character of the bond