Electronegativity
Electronegativity is a measure of the attraction of an atom for electrons in a covalent bond.
Fluorine is the most electronegative atom, while Francium would be the least electronegative. The closer the electronegativity is the more covalent a compound is while I the electronegative difference is big, an ionic bond would be formed.
Intermediate Bonding
Although most compounds are either ionic or covalent there is also the possibility of intermediate bonding. These are compounds that contain atoms with a high charge to surface area ratio, such as Al3+, Be2+ and Li+. The charge: surface area is so big that it will actually polarise the electrons from an anion to form a partial covalent bond, hence the term intermediate bonding.
