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March 26, 2017

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Is a C-H bond polar or non-polar?
Is a C-Cl bond polar or non-polar?

I have different sources giving me different ranges. One says that anything with an electronegetivity of 0.5 or less is non-polar and I have anothre source saying anything 0.3 and less is non-polar. Which one is it?

  • Chem - ,

    The truth is zero.zero is non polar, however, life is on a continium. Most classify .5 or less as "non-polar", however, there is still an electronegativity difference, and there is a polar moment. For other purposes, some use .3 and call that difference "non-polar". I would go with .5, but don't argue the point with your instructor if he says it is .3
    Remember the arguments in Alice in Wonderland? They were very animated, but did not signify much.

  • Chem - ,

    Ok. Thank you :)

  • Chem - ,

    To add to what Bob Pursley has written, let me re-emphasize that from a true perspective only the difference of ZERO give a non-polar bond; however, I have a good friend at the local university (an organic chemist) who tells me that organic chemists consider the difference between C and H to be too small to be considered so he doesn't consider the C-H bond to be polar, even to a small extent. When pressed I can get him to agree that there is a difference but then he returns to the "but it is too small to matter" approach. From a personal standpoint, I call a difference of 1.9 a 50% point, Everything over 1.9 I call ionic and that less than 1.9 I call covalent. Of course those are polar covalent and if we wish to try to cut it closer than that, I suggest to the student that if approximately 2.0 is 50%, then a difference of 1.0 should be about 25% ionic/75% covalent, 0.5 should be about 90% covalent/10% ionic (more or less) and zero should be 100% covalent. Of course this assumes a completely linear relationship for the graph and that isn't quite so but the graph of % ionic character versus electronegativity difference agrees fairly well with those numbers.

  • Chem - ,

    Thank you :)

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