The table below gives approximate Pauling electronegativity values for four elements. Element Electronegativity Na 0.9 Mg 1.2 Cl 3.0 O 3.5 Using these values, which pair of elements would be expected to form a bond with the greatest ionic character?

AS Chemistry 9701: Electronegativity Difference and Ionic Character (MCQ)

Element	Electronegativity
Na	$0.9$
Mg	$1.2$
Cl	$3.0$
O	$3.5$

Element

Electronegativity

0.9

1.2

3.0

3.5

Step 1: Recall the link between electronegativity difference and ionic character

A bond’s character depends on the electronegativity difference between the two atoms involved. A very small difference gives a non-polar covalent bond; a larger difference gives an increasingly polar covalent bond; a very large difference gives a bond with substantial ionic character, since one atom effectively pulls the bonding electrons almost entirely to itself. So the pair with the largest electronegativity difference has the greatest ionic character.

Step 2: Calculate the electronegativity difference for each pair

$\Delta\text{EN}(\text{Na, Cl}) = |0.9 - 3.0| = 2.1$

$\Delta\text{EN}(\text{Mg, O}) = |1.2 - 3.5| = 2.3$

$\Delta\text{EN}(\text{Mg, Cl}) = |1.2 - 3.0| = 1.8$

$\Delta\text{EN}(\text{Na, O}) = |0.9 - 3.5| = 2.6$

Step 3: Identify the greatest difference

Comparing the four values: $1.8 < 2.1 < 2.3 < 2.6$ . The largest difference, $2.6$ , belongs to the Na/O pair.

Why the other options are wrong

A (Na and Cl): a difference of $2.1$ is large enough to be considered ionic (as in real sodium chloride), but it is smaller than the Na/O difference.
B (Mg and O): a difference of $2.3$ is the second-largest, but oxygen is even more electronegative relative to sodium than to magnesium, so Na/O gives a bigger gap.
C (Mg and Cl): this has the smallest difference of the four ( $1.8$ ), so it has the least ionic character of the four pairs listed.

Final answer

Greatest ionic character: Na and O ( $\Delta\text{EN} = \boxed{2.6}$ ), option D.