Problem adding subscripts and superscripts [duplicate]

Question

Possible Duplicate:
Cursive text after _

I need to have some subscripted and superscripted text in my thesis document. But when I try to do it the way as H_{2O} or S^{2}. I get an error at that point and if I compile it anyway I get text with so white spaces for the rest of the line. Like,

H_{2O}helloworldwhyisthishappening

Do I need to use some package to have this functionality? I thought it was standard latex. Or may be it is due to conflict with some package. I'm using the university template so don't quite understand what the problem is. I have put the header section where the packages are called below. Please help.

\usepackage{fancyhdr}   
\usepackage{verbatim}    
\usepackage{acronym}
\usepackage{natbib}
\usepackage{color}
\usepackage[pdftex]{graphicx} 
\usepackage{url}
\usepackage{appendix}
\usepackage[font=small,format=plain,labelfont=bf,up,textfont=it,up]{caption}
\usepackage{tikz}
\usetikzlibrary{arrows,automata}
\usepackage{amsfonts,amssymb,amsbsy,amsmath} 
\usepackage{listings}

Answer 1

If you are typesetting chemical formula, look up the mhchem package. This allows you to typeset chemical formulae easily.

For example: \ce{CO2} has the "2" as a subscript. Neat.

\documentclass{article}
\usepackage{mhchem}
\begin{document}
\ce{H2SO4}
\end{document}

Yields:

Answer 2

The _ and ^ character only work in math-mode. For text you need to use \textsubscript (needs the fixltx2e package) and \textsuperscript instead.

The reason why all the whitespace after H_{2O} is missing is that TeX changing into math-mode at the _ and then all the letters afterwards are set as variables. Also I think you mean H_{2}O (BTW: the braces can be skipped when they include only one character).

Answer 3

No special package but you need to be in math-mode. Use $ $ or \ensuremath{}.

Answer 4

The easiest ways I have found to include super- and subscripts in text mode are shown below. The example is the chemical formula for silicon dioxide:

Method 1:

$\rm SiO_2$

Method 2:

SiO$_2$

I am using MikTeX 2.4 and dvips + ps2pdf, and my PDF output looks good: The letters are definitely in text mode, not math, and the results of the two methods look the same in PDF.

An addendum: If the super- or subscript is an expression, do the following:

C$n$H${2n+2}$

which yields the chemical formula for polyethylene.