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What is the structure of $\ce{Br3O8}$? It has an odd number of electrons; does that make it a free radical?

The structure given in my book shows

enter image description here

Where did the 7th electron of the central atom go?


Picture from book (Pg 265, NCERT Chemistry Part II, class 11):

Pic from book

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The electron didn't go anywhere. It's in an unhybridized p orbital on the central bromine, and yes, $\ce{Br3O8}$ is a free radical. That is why it decomposes above -80ºC.$^{[1]}$


$^{[1]}$ Cotton, F. A. Progress in Inorganic Chemistry - Volume 2; Interscience Publishers: New York, NY, 1960.

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    $\begingroup$ Thanks. That clarifies everything. Isn't it mandatory to mention a free radical to be so in the bond structure? $\endgroup$ – ghosts_in_the_code Feb 14 '17 at 14:18
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    $\begingroup$ Yes, @ghosts. If the structure drawing in your book doesn't indicate in some way that there is a free radical, then it is very likely a misprint. Look closely and make sure there isn't a dot somewhere around the Br atom! $\endgroup$ – Cody Gray Feb 14 '17 at 14:57
  • $\begingroup$ @CodyGray The asterisk has a different meaning indicated in the text. So no dot then :P $\endgroup$ – ghosts_in_the_code Feb 14 '17 at 15:13
  • $\begingroup$ Well, now that you've shown us the picture, I can see that it does give the oxidation states for the bromines. So this is not a misprint, the data is there, you just have to understand it. If this is a textbook, though, I would say that it could be substantially improved by not expecting the student to understand how atomic oxidation states work and explicitly indicating that there is a free radical. $\endgroup$ – Cody Gray Feb 14 '17 at 15:15
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    $\begingroup$ @zwol There are many questions and answers on our site that use NCERT texts. I find them insufficient and outdated at best, sometimes they are even outrageously wrong; it often looks like they have been effortlessly copy & pasted together from already bad sources. $\endgroup$ – Martin - マーチン Feb 15 '17 at 4:50

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