Steve Marsden’s

Chemical bonding is actually a continuum, from very ionic (i.e., complete electron transfer) to pure covalent (i.e., equal electron sharing):

Very ionic¬¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾®Pure Covalent
CsF                                                                                                             I2
Increasing bond "strength"¬¾¾¾®Decreasing bond "strength"

 

One way to express this is as a difference in electronegativity. Similar to electron affinity, this periodic property represents the tendency of an atom to attract electrons shared in a bond .

The trend for electronegativity is the same as for electron affinity and it is quantified with a numerical scale developed by the American chemist Linus Pauling.