# Why don't I get the same value of percentage ionic character of a particular molecule from different equations?

About the ionic character of a polar covalent compound Pauling gave two equations as

1. [1-$e^{.25(x_a - x_b)}]$%
1. [18$(x_a-x_b)^{1.4}$]%

Hanary and Smith gave the equation

1. [$16(x_a-x_b)+3.5(x_a-x_b)^2$]%

Where $x_a$ and $x_b$ stands for the electronegativity of $a$ and $b$ atom in bond $a-b$.

Now if I put $x_a-x_b = 2,$ The 1st, 2nd & 3rd equations respectively give the value as -.648%, 47.5% & 46%. What is the reason behind these different values of percentage ionic character of the same molecule? At where am I wrong?

• You are wrong in thinking that percentage of ionic character is a real observable thing, like mass or energy. It isn't. (Neither is electronegativity, BTW.) – Ivan Neretin May 8 '18 at 5:29
• @IvanNeretin then how Pauling gave the equations and how do we have an electronegativity table? – user187604 May 8 '18 at 11:01
• When Pauling gave the equations, he knew their limitations. As for the electronegativity table, we surely have not one, but many such tables, all subtly different. – Ivan Neretin May 8 '18 at 11:16