Why are bonds with less than a .3 difference in electronegativity nonpolar bonds? For example, if Fe and Co bond, there is a net difference of .1, which a chart in my chemistry book is telling me is considered non-polar covalent. I understand why a change of 1.5 is polar, and a change of 0 is non-polar, but I dont quite understand the .3 cap for non-polar. Do I have inaccurate information, or is there a reason behind this?

Question

Why are bonds with less than a .3 difference in electronegativity nonpolar bonds? For example, if Fe and Co bond, there is a net difference of .1, which a chart in my chemistry book is telling me is considered non-polar covalent. I understand why a change of 1.5 is polar, and a change of 0 is non-polar, but I dont quite understand the .3 cap for non-polar. Do I have inaccurate information, or is there  a reason behind this?

aaronq · Answer

my guess is that they don't have enough polarity to give the molecule a significant dipole moment, plus Co and Fe will probably not bond to each other in regular circumstances.

anonymous · Answer

It's totally arbitrary.   Someone just picked a number that divides bonds you can most usefully consider polar from those the polarity of which is usually too small to matter.