Cursive text after _

Question

I would like to write H2O with a small 2 below the H.

H_2 O (water)

However, all text after _2 becomes cursive. It appear that something obvious is wrong but, I cant find what it is.

Anyone how have had the same problem?

it is hard to tell, however, the _ needs to be in a math mode to be subscripted. So do H$_2$O. — nickpapior, Dec 16 '12 at 20:09
Besides the fact that _ is only valid in math-mode (and LaTeX probably used math-mode from _2 on and didn’t know where to stop), \textsubscript{2} also works mostly. If you find yourself often using chemical formulae you might be interested in certain packages. — Qrrbrbirlbel, Dec 16 '12 at 20:11
@RollerBoy, you probably (as Gonzalo also indicates) use the mhchem package. It is much inferior in use and can do a lot of stuff! :) — nickpapior, Dec 16 '12 at 20:57

Gonzalo Medina · Answer 1 · 2012-12-16T21:31:03.753

13

Hard to tell without seeing the actual code you are using; anyways, I'd suggest you the mhchem package:

\documentclass{article}
\usepackage{mhchem}

\begin{document}

\ce{H2O}

\end{document}

enter image description here

Another option would be to use the chemmacros package:

\documentclass{article}
\usepackage{chemmacros}

\begin{document}

\ch{H2O}

\end{document}

However, for just one or two formulae, using a package might be overkill, and you could simply say something like

\documentclass{article}

\begin{document}

$\mathrm{H}_2\mathrm{O}$

\end{document}

Or using a command, as cgnieder suggested,

\documentclass{article}
\newcommand*\chem[1]{\ensuremath{\mathrm{#1}}}

\begin{document}

\chem{H_2O}

\end{document}

edited Dec 16 '12 at 21:31

answered Dec 16 '12 at 20:09

Gonzalo Medina

2

Similar with chemmacros (\ch{H2O}). The package is probably overkill, though, if one only needs one or two chemical formulas. – cgnieder Dec 16 '12 at 20:12
I not having too much chemical formulas to write so $_2$ will do, but anyway Thanks – RollerBoy Dec 16 '12 at 20:26
@RollerBoy I added another options to my answer; I wouldn't use just $_2$ please see my last example. – Gonzalo Medina Dec 16 '12 at 20:27
3

@RollerBoy how about saying \newcommand*\chem[1]{\ensuremath{\mathrm{#1}}} in the preamble and then use it like \chem{H_2O}? – cgnieder Dec 16 '12 at 20:32
@cgnieder I've added your two suggestions to my answer; thank you! – Gonzalo Medina Dec 16 '12 at 21:23
@cgnieder This is indeed a place where \ensuremath can be really useful. – egreg Dec 16 '12 at 21:25
@egreg They're rare but there are use cases ;) – cgnieder Dec 16 '12 at 21:40

1 Answers1