# Why are alkanes 'non-polar'

I am unsure with regards to the specific reason why alkanes are non-polar as I have heard different explanations. My teacher said that it is because, although there is a difference in electronegativity between carbon and hydrogen atoms, the carbon is shielded by the hydrogen atoms from reacting with the external environment and therefore, since only the hydrogen can react, it is non-polar (something along the lines of it is the difference between delta + and delta - ends that actually make a molecule polar). From searching on the internet, however, I have found the explanation that it is because the difference in electronegativity is so small (0.3) that it is non-polar, which makes sense, however it contradicts what my textbook states: That only bonds between elements with equal electronegativity are non-polar. Can someone clear this up for me? Thank you!

• It is just a matter of semantics. The difference in electronegativity between C and H is just so small that, for all intents and purposes, the bond (and the molecule) is practically non-polar. Dec 7 '15 at 12:48
• In addition, unsubstituted, symmetrical alkanes, e.g. methane, are even less polar (though there is still a small instantaneous dipole moment). See butane.chem.uiuc.edu/cyerkes/Chem104ACSpring2009/… Dec 8 '15 at 1:58
• so it does not have anything too do with the fact that carbon is 'on the inside' and therefore cant interact with the outside environment that it is not polar? Dec 8 '15 at 17:10
• @frostedcake No, it doesn't. Also, there is quite a set of polar hydricarbons like azulene Jan 14 '16 at 17:52
• This highlights a common theme throughout much of science. Very rarely are two things exactly equal. The question to ask is, "are they 'equal enough' that we can't really tell a difference between them?" In this case, the electronegativities of $\ce C$ and $\ce H$ are "equal enough" to make alkanes non-polar. Jan 14 '16 at 19:27