# Using only electronegativity, which bond would have the greatest percent ionic character?

May 7, 2017

We know or should know that $\text{electronegativity}$ is defined as the ability of an atom involved in a chemical bond to polarize electron density towards itself. Electronegativity decreases across the Period, i.e. INCREASES across a row of the Periodic Table, from left to right as we face the Table, BUT DECREASES down a Group, a column of the Periodic Table. This is the result of progressively increasing nuclear charge that is shielded very poorly by INCOMPLETE valence electronic shells.
Now $c$ and $d$ both combine an alkali metal (an element that should be very POORLY electronegative!) with a Group 17 halogen, an atom that because of its nuclear charge and its Periodic position, should be VERY ELECTRONEGATIVE. Because potassium is LESS electronegative than sodium, $\text{option c.}$ is the required answer, because here the GREATEST difference in electronegativity is observed.