IMAT 2012 Q66 [Covalent Bonds]

The positions of some elements in the Periodic Table are shown below.

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Which one of the following pairs of elements is most likely to form a covalent bond?

A. magnesium and bromine
B. strontium and oxygen
C. potassium and chlorine
D. calcium and chlorine
E. beryllium and iodine

The trick that comes with this question is that all the bonds are supposedly ionic, but the question is actually testing your knowledge on Electronegativity.

We know that the greater the difference in electronegativity would account for an ionic bond- so the smallest difference would give us a bond that could be considered covalent, or showing covalent characteristics.

If we know that electronegativity is strongest as so:

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Then the smallest difference in electronegativity, or the weakest, would be an element from the bottom right alongside an element from the top left.

A could be a viable option.
B is incorrect, as the difference in electronegativity would be larger, resulting in an ionic bond.
C and D also incorrect for the same reason.
E is another viable option.

So between A and E; Beryllium and Iodine have a more similar electronegativity and that could result in a covalent like bond. Therefore our answer is E.

For reference;

Beryllium has an electronegativity of 1.57 and Iodine has an electronegativity of 2.66. Their difference would be around 1.09.

Magnesium has an electronegativity of 1.31 and Bromine has an electronegativity of 2.96. Their difference would be around 1.65.