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I have heard that Avogadro's number, $N_\mathrm A=6.022 \times 10^{23}$, is the number of atoms contained in $12$ grams of $\ce{^{12}C}$. I think it should be an integer, but I couldn't find the exact number. Is it an integer?

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marked as duplicate by Mithoron, Nilay Ghosh, aventurin, Waylander, M.A.R. May 22 '18 at 21:22

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    $\begingroup$ There is no exact value. The value with something like a dozen decimal digits you might have seen in a textbook is as exact as it gets. $\endgroup$ – Ivan Neretin May 22 '18 at 15:15
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    $\begingroup$ It is nonetheless an integer, for sure. You can't have half an atom. $\endgroup$ – Felipe S. S. Schneider May 22 '18 at 15:37
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    $\begingroup$ @FelipeS.S.Schneider You're assuming that 12 g is such that an integral number of carbon-12 atoms go into it? $\endgroup$ – Zhe May 22 '18 at 15:41
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    $\begingroup$ The old (1971 I guess) definition of mole that you stated surely leads to floating point numbers (although only if you measure weights with more than 23 significant digits). The new definition (2018) fixes one mole to be exactly $6.02214076 \times 10^{23}$, which is an integer. $\endgroup$ – Felipe S. S. Schneider May 22 '18 at 16:09
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    $\begingroup$ I stand corrected. As @Felipe says, since very recently there is an exact value, and (not that it is of any slightest importance) it is an integer. $\endgroup$ – Ivan Neretin May 22 '18 at 17:07

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