I have written a Chemical Bond Polarity Calculator application, which many students use for their homework. I sometimes get questions from these students as to why the cutoff I use is 2.0, and not some other number between 1.7 and 2.1. I understand that there is no hard and fast rule as to what the cutoff should be. I just want to know what a real chemist (I'm a computer programmer, not a chemist) would want this particular application to use for the cutoff. Conversely, would a real chemist want to be able to input the cutoff themselves?

This post indicates that 2.1 is a good cutoff, and this post indicates the number should be between 1.7 and 1.9. How would the real chemists out there recommend I modify this application?

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    $\begingroup$ I don't know to what extent this answers your question, but I'll just drop my 2 cents about "getting questions from these students". Just be honest. Tell them it's arbitrary. Tell them that someone just threw darts and decided that 2.0 is a good cutoff and that in reality there's a whole spectrum between ionic and covalent and if they want to use 1.7 as their cutoff, so be it. Just that the teacher will be using 2.0 so it's probably easier for them to stick to 2.0 so that they're on the same page as the rest of the class. $\endgroup$ Oct 2, 2015 at 17:16


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