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I am trying to denote a 28Si isotope. I used $^{28}Si$. In the output, the chemical symbol is in italics, also there is an unnecessary space between the symbol and the nucleon number.

How do I get the chemical symbol 'Si' in roman, and the superscript and symbol a bit closer? I will use this code to denote a label in a Python code graph.

marked as duplicate by clemens, Stefan Pinnow, Zarko, Sean Allred, Andrew Aug 4 '16 at 12:02

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    Have you tried ${}^{28}$Si? – Mico Aug 3 '16 at 4:55
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    I have a feeling this posting is a dupe, but I haven't found a suitable earlier posting yet. – Mico Aug 3 '16 at 5:11
  • @Mico You mean this question: tex.stackexchange.com/questions/319325/… – Ross Aug 3 '16 at 7:15

I'm not sure how nobody has posted mhchem, the canonical chemistry package! Straight from the manual, section "Isotopes":





I have some \ce{^{227}_{90}Th+} lying around.



(\ce stands for "chemical equation" and can be used in either math or text mode.)

If you're doing other stuff with chemistry, this is the package you want. Check out the docs!

  • 11
    Please clear your desk of this Thorium and bin it appropriately within the next 18.68 days. – Joce Aug 3 '16 at 8:18

Smaller and lighter than mhchem is the isotope package.

Usage looks roughly like:


\isotope{Po} --- \isotope[56]{Fe} --- \isotope[13][6]{C}\\

$\isotope{n} + \isotope{H} \to \isotope{D} +
\gamma(2.2\,\mathrm{MeV})$ \\

$\isotope[13]{C} + \alpha(5.314\,\mathrm{MeV}) \to
\isotope[16]{O}^{**} + n$

resulting in

enter image description here


You may wish to define a macro to typeset isotopes, say,


Use the macro as follows: \isotope{Si}{28}.

This approach avoids the use of math mode and associated low-level solutions such as ${}^{28}$Si.


You could use any of the following:

  1. ${}^{28}$Si
  2. ${}^{28}\mbox{Si}$
  3. ${}^{28}\text{Si}$, you need to load amstext package.
  4. ${}^{28}\mathrm{Si}$
  5. ${}^{28}{\rm Si}$
  • You may wish to add a note that while the fifth method works with the "standard" LaTeX document classes (article, report, and book), it generates a warning message with the KOMA-Script document classes and crashes with the memoir document class. Since other, perfectly valid and general, solution methods are available, it may not be a good idea to even present method 5. – Mico Aug 3 '16 at 5:09
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    Acceptable are 2. and 4. In 1. and partially 3. a logic of expression is lost. In 5. we have \rm, deprecated in LaTeX. – Przemysław Scherwentke Aug 3 '16 at 5:20
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    @PrzemysławScherwentke 4 is probably how I'd do it for a one-off. But the logic is already broken assuming you write "I have a 4 Si wafers but only one of them is $^{28}\mathrm{Si}$" – Chris H Aug 3 '16 at 8:16
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    although method 3 may look attractive, if it happens to be embedded in a context that is in italic, the Si will also be set italic, which is wrong. using one of the "chemistry" packages is really the best way to approach this. – barbara beeton Aug 3 '16 at 21:44

If you can use additional packages:


More effective than

is (with tensor package):



Additional remarks are here: How to reduce the spacing in chemical symbols?

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