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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    $\begingroup$ 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. $\endgroup$ May 22, 2018 at 15:15
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    $\begingroup$ It is nonetheless an integer, for sure. You can't have half an atom. $\endgroup$ May 22, 2018 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, 2018 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. $\endgroup$ May 22, 2018 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. $\endgroup$ May 22, 2018 at 17:07


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