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Can ionic character also be construed as a poor sharing of electrons rather than simply as the taking of electrons? For example, NaCl is ionic, and that's because the chlorine takes sodium's one valence electron. On the other hand, C-Br and C-I are sometimes referred to as ionic (at least informally).

Is it proper to refer to C-Br and C-I as ionic because of the poor overlap between carbon and the two respective halides rather than any electron-withdrawing effect per se; the EN difference between C and I is less than the EN difference in the "non-polar" C-H bond.

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  • $\begingroup$ Is it proper to refer to C-Br and C-I as ionic because of the poor overlap between carbon and the two respective halides rather than any electron-withdrawing effect per se? No, they are certainly not ionic per se. Have a look here and here. $\endgroup$ – Philipp Sep 6 '14 at 22:23
  • $\begingroup$ Good point, ionic things have a crystal structure. $\endgroup$ – Dissenter Sep 6 '14 at 22:24
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Is it proper to refer to C-Br and C-I as ionic

I've never thought of those bonds as ionic. For example, consider electrophilic aromatic substitution in bromobenzene. The sigma bond between the bromine and benzene carbon allows for inductive withdrawal of electron density from the benzene ring, hence bromobenzene typically reacts slower than benzene. However, to explain the ortho-para directing effect of the halogen you also need to invoke resonance interaction between the halogen and the benzene carbon p orbital. So there is both sigma and pi interaction between a halogen substituent and an aromatic carbon, that doesn't sound ionic to me.

BTW, even in the case of sodium chloride the electron is not completely transferred from sodium to chlorine. Crude estimates using this methodology put it around 80%.

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  • $\begingroup$ Perhaps polar covalent is a better term? $\endgroup$ – Dissenter Sep 6 '14 at 22:29
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    $\begingroup$ Yes, that's a good way to describe it. $\endgroup$ – ron Sep 6 '14 at 22:34

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