How to figure out whether a bond is more ionic than covalent?

Apr 8, 2015

For example:

NaCl and ${H}_{2} O$

NaCl is an ionic compound because the difference in electronegatity is 2.1 (Cl is 3.0 and Na is 0.9). If the result is bigger than (around) 1.8 we are talking about ionic compound.

${H}_{2} O$ is a covalent compound because the difference in electronegatity is 1.3 (H is 2.2 and O is 3.5). If the result is smaller than (around) 1.8 we are talking about covalent compound. Of course, this compound is polar or it has covalent bond with ionic character (oxygen is negative pole, and hydrogen is positive pole).

Apr 8, 2015

If the electronegativity difference between the two elements is greater than or equal to 1.7, the bond is more ionic than covalent.

There are several formulas for calculating percent ionic character.

They give a fair correlation with ionic character as determined by dipole moments.

The formula proposed by Pauling is

"% ionic character" = (1 – e^(-1/4(χ_A – χ_B)^2)) × 100 %

Here's how it fits for a number of compounds. If |χ_A – χ_B| = 1.7, the predicted ionic character is 51 %.

The predicted ionic character for HF is 55 %.