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authorNorbert Preining <norbert@preining.info>2020-02-02 03:02:06 +0000
committerNorbert Preining <norbert@preining.info>2020-02-02 03:02:06 +0000
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+% !arara: pdflatex
+% !arara: biber
+% arara: pdflatex
+% arara: pdflatex
+% --------------------------------------------------------------------------
+% the CHEMFORMULA package
+%
+% typeset chemical compounds and reactions
+%
+% --------------------------------------------------------------------------
+% Clemens Niederberger
+% --------------------------------------------------------------------------
+% https://github.com/cgnieder/chemformula/
+% contact@mychemistry.eu
+% --------------------------------------------------------------------------
+% If you have any ideas, questions, suggestions or bugs to report, please
+% feel free to contact me.
+% --------------------------------------------------------------------------
+% Copyright 2011--2020 Clemens Niederberger
+%
+% This work may be distributed and/or modified under the
+% conditions of the LaTeX Project Public License, either version 1.3
+% of this license or (at your option) any later version.
+% The latest version of this license is in
+% http://www.latex-project.org/lppl.txt
+% and version 1.3 or later is part of all distributions of LaTeX
+% version 2005/12/01 or later.
+%
+% This work has the LPPL maintenance status `maintained'.
+%
+% The Current Maintainer of this work is Clemens Niederberger.
+% --------------------------------------------------------------------------
+\documentclass{chemformula-manual}
+
+\addbibresource{cnltx.bib}
+
+\chemsetup{
+ greek = newtx ,
+ modules = {redox,reactions,units} ,
+ formula = chemformula ,
+ chemformula/format = \libertineLF
+}
+
+\usepackage[accsupp]{acro}
+\acsetup{
+ long-format = \scshape ,
+ short-format = \scshape
+}
+\DeclareAcronym{iupac}{
+ short = iupac ,
+ long = International Union of Pure and Applied Chemistry ,
+ pdfstring = IUPAC ,
+ accsupp = IUPAC
+}
+
+\sisetup{
+ detect-mode=false,
+ mode=text,
+ text-rm=\libertineLF
+}
+
+\usepackage{filecontents}
+
+\defbibheading{bibliography}{\section{References}}
+\addbibresource{\jobname.bib}
+\begin{filecontents*}{\jobname.bib}
+@book{iupac:greenbook,
+ author = {E. Richard Cohan and Tomislav Cvita\v{s} and Jeremy G. Frey and
+ Bertil Holmstr\"om and Kozo Kuchitsu and Roberto Marquardt and Ian Mills and
+ Franco Pavese and Martin Quack and J\"urgen Stohner and Herbert L. Strauss and
+ Michio Takami and Anders J Thor} ,
+ title = {``Quantities, Symbols and Units in Physical Chemistry'', \acs{iupac}
+ Green Book} ,
+ sorttitle = {Quantities, Symbols and Units in Physical Chemistry} ,
+ indexsorttitle = {Quantities, Symbols and Units in Physical Chemistry} ,
+ edition = {3rd Edition. 2nd Printing} ,
+ year = {2008} ,
+ publisher = {\acs{iupac} \&\ RSC Publishing, Cambridge}
+}
+\end{filecontents*}
+
+\DeclareInstance{xfrac}{chemformula-text-frac}{text}
+ {
+ scale-factor = 1 ,
+ denominator-bot-sep = -.2ex ,
+ denominator-format = \scriptsize #1 ,
+ numerator-top-sep = -.2ex ,
+ numerator-format = \scriptsize #1 ,
+ slash-right-kern = .05em ,
+ slash-left-kern = .05em
+ }
+
+\newpackagename\chemmacros{chemmacros}
+
+\newidxcmd\manual{\textsf{#1}}[\ (manual)]
+\newidxcmd\arrowtype{\code{#1}}[\ (arrow type)]
+
+\makeatletter
+\newcommand*\cf@arrow{%
+ \@ifstar
+ {\cf@arrow@star}
+ {\cf@arrow@nostar}%
+}
+\newrobustcmd*\cf@arrow@star[1]{%
+ \@ifnextchar[
+ {\cf@arrow@star@opt{#1}}
+ {\cf@arrow@star@opt{#1}[]}%
+}
+\newrobustcmd*\cf@arrow@nostar[1]{%
+ \@ifnextchar[
+ {\cf@arrow@nostar@opt{#1}}
+ {\cf@arrow@nostar@opt{#1}[]}%
+}
+\def\cf@arrow@star@opt#1[#2]{%
+ \ifblank{#2}
+ {\item\arrowtype*{#1}}
+ {\item\arrowtype*{#1}#2}%
+ \cnltx@checkdefault{\hfill\newline}%
+}
+\def\cf@arrow@nostar@opt#1[#2]{%
+ \ifblank{#2}
+ {\item\arrowtype{#1}}
+ {\item\arrowtype{#1}#2}%
+ \cnltx@checkdefault{\hfill\newline}%
+}
+
+\newenvironment{codedesc}
+ {%
+ \def\Code##1{\item\code{##1}\hfill\newline}%
+ \cnltxlist
+ }
+ {\endcnltxlist}
+
+\newenvironment{arrows}
+ {%
+ \let\arrow\cf@arrow
+ \cnltxlist
+ }
+ {\endcnltxlist}
+\makeatother
+
+\renewcommand*\AmS{\hologo{AmS}}
+
+\newcommand*\TikZ{Ti\textit{k}Z}
+
+\newname\hensel{Martin Hensel}
+
+\begin{document}
+
+\section{Introduction}
+Probably every chemist using \LaTeXe\ is aware of the great \pkg{mhchem}
+package by \hensel. There have always been some difficulties intertwining it
+with the \chemmacros\ package, though. Also, some other minor points in
+\pkg{mhchem} always bothered me, but they hardly seemed enough for a new
+package. They weren't even enough for a feature request to the \pkg{mhchem}
+author. The challenge and the fun of creating a new package and the wish for
+a highly customizable alternative led to \chemformula\ after all.
+
+\chemformula\ works very similar to \pkg{mhchem} but is more strict as to how
+compounds, stoichiometric factors and arrows are input. In the same time
+\chemformula\ offers \emph{many} possibilities to customize the output.
+
+\section{Licence and Requirements}
+\license
+
+The \chemformula\ package needs and thus loads the packages
+\bnd{l3kernel}~\cite{bnd:l3kernel}, \pkg{xparse}, \pkg{l3keys2e} and
+\pkg{xfrac} (all three are part of the \bnd{l3packages}
+bundle~\cite{bnd:l3packages}),
+\pkg{tikz}\footnote{\CTANurl[graphics]{pgf}}~\cite{pkg:pgf},
+\pkg{amstext}~\cite{pkg:amstext}, \pkg{nicefrac}~\cite{pkg:nicefrac} and
+\pkg{scrlfile} (from the \KOMAScript\footnote{\CTANurl{koma-script}}
+bundle~\cite{bnd:koma-script}).
+
+\section{Setup}
+
+If you're using \chemformula\ as a standalone package options are set up with
+the following command:
+\begin{commands}
+ \command{setchemformula}[\marg{options}]
+ Set up \chemformula.
+\end{commands}
+
+\chemformula\ is tightly intertwined with the \chemmacros\ package. If both
+packages are loaded together, \chemformula\ is integrated into the
+\chemmacros\ package. Then all of \chemformula's options belong to
+\chemmacros' module \module{chemformula}. This means if you load it via
+\chemmacros\ or in addition to \chemmacros\ they can be setup with
+\begin{commands}
+ \command{chemsetup}[\Oarg{chemformula}\marg{options}]
+ Set up options for \chemformula\ exclusively, or
+ \command{chemsetup}[\Marg{chemformula/\meta{option1},chemformula/\meta{option2}}]
+ Set up options for \chemformula\ together with others of \chemmacros'
+ options.
+\end{commands}
+
+\section{The Basic Principle}
+\chemformula\ offers one main command.
+\begin{commands}
+ \command{ch}[\oarg{options}\marg{input}]
+ \chemformula's main command.
+\end{commands}
+The usage will seem very familiar to you if you're familiar with \pkg{mhchem}:
+\begin{example}[side-by-side]
+ \ch{H2O} \par
+ \ch{Sb2O3} \par
+ \ch{H+} \par
+ \ch{CrO4^2-} \par
+ \ch{AgCl2-} \par
+ \ch{[AgCl2]-} \par
+ \ch{Y^{99}+} \par
+ \ch{Y^{99+}} \par
+ \ch{H2_{(aq)}} \par
+ \ch{NO3-} \par
+ \ch{(NH4)2S} \par
+ \ch{^{227}_{90}Th+} \par
+ $V_{\ch{H2O}}$ \par
+ \ch{Ce^{IV}} \par
+ \ch{KCr(SO4)2 * 12 H2O}
+\end{example}
+
+However, there are differences. The most notable one: \chemformula\
+distinguishes between different types of input. These different parts
+\emph{have} to be separated with blanks:
+\begin{commands}
+ \command{ch}[\Marg{part1 part2 part3 part4}]
+\end{commands}
+A blank in the input \emph{never} is a blank in the output. This role of the
+blank strictly holds and disregarding it can have unexpected results and even
+lead to errors.
+
+The most visible differences regard spacing and the shapes of the default
+arrows:
+\begin{example}[side-by-side]
+ \ch{A + B ->[a] C} \par
+ \ce{A + B ->[a] C}
+\end{example}
+
+This means that \cs{ch}\Marg{2H2O} is recognized as a \emph{single} part,
+which in this case is recognized as a compound.
+\begin{example}[side-by-side]
+ \ch{2H2O} \par
+ \ch{2 H2O}
+\end{example}
+This also means, that a part cannot contain a blank since this will
+automatically divide it into two parts. If you need an extra blank in the
+output you need to use \verbcode+~+ or \cs*{~}. However, since commands
+in most cases gobble a space after them a input like
+\cs{ch}\Marg{\cs*{command} ABC} will be treated as a single part. If you want
+or need to divide them you need to add an empty group:
+\cs{ch}\Marg{\cs*{command}\marg{} ABC}. The different input types are
+described in the following sections.
+
+\section{Stoichiometric Factors}
+A stoichiometric factor may only contain of numbers and the signs
+\verbcode+.,_/()+
+\begin{example}[side-by-side]
+ \ch{2} \par
+ \ch{12}
+
+ % decimals:
+ \ch{.5} \par
+ \ch{5,75}
+
+ % fractions:
+ \ch{3/2} \par
+ \ch{1_1/2}
+
+ % ``iupac'':
+ \ch{(1/2)}
+\end{example}
+
+As you can see if you input decimal numbers a missing leading zero is added.
+
+You have to be a little bit careful with the right syntax but I believe it is
+rather intuitive.
+\begin{sourcecode}
+ this won't work but will result in an error: \ch{1/1_1}
+\end{sourcecode}
+
+If stoichiometric factors are enclosed with parentheses the fractions are not
+recognized and missing leading zeros are not added. What's inside the
+parentheses is typeset as is.
+\begin{example}
+ \ch{(1/2) H2O} \ch{1/2 H2O} \ch{0.5 H2O}
+\end{example}
+You can find many examples like the following for stoichiometric factors in
+parentheses in the \acs{iupac} Green Book~\cite{iupac:greenbook}:
+\begin{reaction*}
+ (1/5) K "\ox{7,Mn}" O4 + (8/5) HCl == (1/5) "\ox{2,Mn}" Cl2 + (1/2) Cl2 + (1/5) KCl + (4/5) H2O
+\end{reaction*}
+
+There are a few possibilities to customize the output.
+\begin{options}
+ \keyval{decimal-marker}{marker}\Default{.}
+ The symbol to indicate the decimal.
+ \keychoice{frac-style}{math,xfrac,nicefrac}\Default{math}
+ Determines how fractions are displayed.
+ \keyval{frac-math-cmd}{command sequence}\Default{\cs*{frac}}
+ \sinceversion{4.1}Allows you to choose which command is used with
+ \keyis{frac-style}{math}. This needs to be a command sequence that takes
+ two arguments that are set in math mode.
+ \keyval{stoich-space}{skip}\Default{.1667em plus .0333em minus .0117em}
+ The space that is placed after the stoichiometric factor. A rubber
+ length.
+ \keybool{stoich-paren-parse}\Default{false}
+ If set to true stoichiometric factors enclosed by parentheses also are
+ parsed.
+ \keyval{stoich-print}{cs}\Default{\cs{chstoich}}
+ This option allows to redefine the macro that prints the stoichiometric
+ factors. \meta{cs} should be a macro that takes one mandatory argument.
+ \emph{Please note that using this option will disable \chemformula's
+ stoichiometric parsing as that is done by the default command
+ \cs{chstoich}.}
+\end{options}
+
+\begin{example}
+ \ch[decimal-marker={,}]{3.5} \ch[decimal-marker={$\cdot$}]{3,5}
+\end{example}
+
+The option \keyis{frac-style}{xfrac} uses the \cs*{sfrac} command of the
+\pkg{xfrac} package. The output strongly depends on the font you use.
+\begin{example}
+ \ch[frac-style=xfrac]{3/2} \ch[frac-style=xfrac]{1_1/2}
+\end{example}
+\chemformula\ defines the instance \code{chemformula-text-frac} which you can
+redefine to your needs. See the \pkg{xfrac} documentation for further
+information. The default definition is this:
+\begin{sourcecode}
+ \DeclareInstance{xfrac}{chemformula-text-frac}{text}
+ {
+ slash-left-kern = -.15em ,
+ slash-right-kern = -.15em
+ }
+\end{sourcecode}
+This document uses the font Linux Libertine~O and the following definition:
+\begin{sourcecode}
+ \DeclareInstance{xfrac}{chemformula-text-frac}{text}
+ {
+ scale-factor = 1 ,
+ denominator-bot-sep = -.2ex ,
+ denominator-format = \scriptsize #1 ,
+ numerator-top-sep = -.2ex ,
+ numerator-format = \scriptsize #1 ,
+ slash-right-kern = .05em ,
+ slash-left-kern = .05em
+ }
+\end{sourcecode}
+
+The option \keyis{frac-style}{nicefrac} uses the \cs*{nicefrac} command of the
+\pkg{nicefrac} package.
+\begin{example}
+ \ch[frac-style=nicefrac]{3/2} \ch[frac-style=nicefrac]{1_1/2}
+\end{example}
+
+The option \option{stoich-space} allows you to customize the space between
+stoichiometric factor and the group following after it.
+\begin{example}[side-by-side]
+ \ch{2 H2O} \par
+ \ch[stoich-space=.3em]{2 H2O}
+\end{example}
+
+\section{Compounds}\label{ssec:compounds}
+\chemformula\ determines compounds as the type that ``doesn't fit in anywhere
+else.'' This point will become more clear when you know what the other types
+are.
+\begin{example}[side-by-side]
+ \ch{H2SO4} \par
+ \ch{[Cu(NH3)4]^2+}
+\end{example}
+
+\subsection{Adducts}
+\chemformula\ has two identifiers which will create adducts.
+\begin{commands}
+ \command{ch}[\Marg{A.B}] \ch{A.B}
+ \command{ch}[\Marg{A*B}] \ch{A*B}
+\end{commands}
+\begin{example}[side-by-side]
+ \ch{CaSO4.H2O} \par
+ \ch{CaSO4*H2O}
+\end{example}
+Since numbers in a compound always are treated as subscripts (see
+section~\ref{ssec:subscripts}) you sometimes need to introduce stoichiometric
+factors for the right output:
+\begin{example}[side-by-side]
+ \ch{Na3PO4*12H2O} \par
+ \ch{Na3PO4* 12 H2O} \par
+ \ch{Na3PO4 * 12 H2O}
+\end{example}
+
+\subsection{Subscripts}\label{ssec:subscripts}
+\emph{All} numbers in a compound are treated as subscripts.
+\begin{example}[side-by-side]
+ \ch{H2SO4}
+\end{example}
+If you want a letter to be a subscript you can use the math syntax:
+\begin{example}[side-by-side]
+ \ch{A_nB_m}
+\end{example}
+The subscript recognizes groups. You can also use math inside it.
+\begin{example}[side-by-side]
+ \ch{A_{$n$}B_{$m$}} \par
+ \ch{NaCl_{(aq)}}
+\end{example}
+
+\subsection{Commands}
+Commands are allowed in a compound:
+\begin{example}[side-by-side]
+ \ch{\textbf{A2}B3} \ch{A2\color{red}B3}
+\end{example}
+
+However, if the commands demand numbers as argument, \eg, space commands or
+\chemmacros' \verbcode+\ox+ command the direct use will fail. This is
+because the numbers are treated as subscripts \emph{before} the command
+expands.
+\begin{sourcecode}
+ \ch{A\hspace{2mm}B} will raise an error because \hspace sees something like
+ this: \hspace{$_2$mm}. Actually not at all like this but equally bad\ldots
+\end{sourcecode}
+See section~\ref{ssec:text} for a way around this.
+
+Please also note that formulas are placed inside a group!
+\begin{example}[side-by-side]
+ \ch{A2\color{red}B3 C4}
+\end{example}
+
+\subsection{Charges and Other Superscripts}
+\paragraph{Basics}
+If a compound \emph{ends} with a plus or minus sign it will be treated as
+charge sign and typeset as superscript. In other places a plus is treated as
+a triple bond and a dash will be used as a single bond, see
+section~\ref{ssec:bonds}.
+\begin{example}[side-by-side]
+ \ch{A+B} \ch{AB+} \par
+ \ch{A-B} \ch{AB-}
+\end{example}
+
+For longer charge groups or other superscripts you can use the math syntax.
+It recognizes groups and you can use math inside them. Inside these groups
+neither \code{+} nor \code{-} are treated as bonds. If a dot \code{.} is
+inside a superscript it is treated as indicator for a radical. A \code{*}
+gives the excited state.
+\begin{example}[side-by-side]
+ \ch{A^{x-}} \par
+ \ch{A^x-} \par
+ \ch{A^{x}-} \par
+ \ch{A^{$x-$}} \par
+ \ch{RNO2^{-.}} \par
+ \ch{^31H} \par
+ \ch{^{14}6C} \par
+ \ch{^{58}_{26}Fe} \par
+ \ch{NO^*}
+\end{example}
+
+Actually\changedversion{4.5a} a dot \code{.} is not always treated as
+indicator for a radical: if the dot in the superscript is followed by a number
+it is interpreted as a decimal sign. It is typeset according to the option
+\option{decimal-marker}. This may be a good place to mention that a comma
+\code{,} in a superscript is also typeset according to
+\option{decimal-marker}.
+
+\begin{example}[side-by-side]
+ \ch{^{22,98}_{11}Na}
+ \ch{^{22.98}_{11}Na}\par
+ \setchemformula{decimal-marker={,}}
+ \ch{^{22,98}_{11}Na}
+ \ch{^{22.98}_{11}Na}
+\end{example}
+
+Ions and ion composites with more than one charge can be typeset quite as
+easy:
+\begin{example}[side-by-side]
+ \ch{SO4^2-} \ch{Ca^2+ SO4^2-}
+\end{example}
+
+\paragraph{Charge Commands}
+You don't need to use \cs{mch} and related commands inside \cs{ch}. Indeed,
+you \emph{shouldn't} use them as they might mess with the subscript and
+superscript alignment. The \chemmacros\ option \code{circled} is obeyed by
+\cs{ch}.
+\begin{example}
+ \chemsetup[charges]{circled=all}
+ \ch{H+ + OH- <=> H2O}
+\end{example}
+
+\chemformula\ knows the options \option{circled} and \option{circletype} also
+on its own.
+
+\begin{example}
+ \setchemformula{circled=all}
+ \ch{H+ + OH- <=> H2O}
+\end{example}
+
+These options are coupled with \chemmacros\ options, \ie, setting \chemmacros'
+options will also set \chemformula's equivalents. The other way around the
+options act independently: setting \chemformula's options will \emph{not} set
+\chemmacros' options.
+\begin{options}
+ \keychoice{circled}{formal,\default{all},none}\Default{formal}
+ \chemformula\ uses two different kinds of charges which indicate the usage
+ of real ($+/-$) and formal (\fplus/\fminus) charges. The choice
+ \code{formal} distinguishes between them, choice \code{none} displays them
+ all without circle, choice \code{all} circles all.
+ % circletype
+ \keychoice{circletype}{\default{chem},math}\Default{chem}
+ This option switches between two kinds of circled charge symbols:
+ \cs{fplus} \fplus\ and \verbcode+$\oplus$+ $\oplus$.
+\end{options}
+
+\paragraph{Behaviour}
+The supercripts behave differently depending on their position in a compound,
+if there are super- and subscripts following each other directly.
+\begin{example}
+ \ch{^33B} \ch{{}^33B} \ch{3^3B} \ch{B^3} \ch{B3^3} \par
+ \ch{^{23}_{123}B} \ch{{}^{23}_{123}B} \ch{_{123}^{23}B}
+ \ch{B^{23}} \ch{B_{123}^{23}} \par
+ \ch{^{123}_{23}B} \ch{{}^{123}_{23}B} \ch{_{23}^{123}B}
+ \ch{B^{123}} \ch{B23^{123}}
+\end{example}
+\begin{itemize}
+ \item If a compound \emph{starts} with a sub- or superscript both sub- and
+ superscript are aligned to the \emph{right} else to the \emph{left}.
+ \item If a compound \emph{does not start} with a sub- or superscript and
+ there is both a sub- and a superscript, the superscript is shifted
+ additionally by a length determined from the option
+ \key{charge-hshift}{dim}, also see page~\pageref{desc:charge-hshift}f.
+\end{itemize}
+The second point follows \ac{iupac}'s recommendations:
+\begin{cnltxquote}[{\acs{iupac} Green Book {\cite[][p.\,51]{iupac:greenbook}}}]
+ In writing the formula for a complex ion, spacing for charge number can be
+ added (staggered arrangement), as well as parentheses:
+ \ch[charge-hshift=full]{SO4^2-}, \ch{(SO4)^2-}. The staggered arrangement
+ is now recommended.
+\end{cnltxquote}
+
+\subsection{Bonds}\label{ssec:bonds}
+\subsubsection{Native Bonds}
+There are three kinds of what I will call ``native bonds'':
+\begin{example}[side-by-side]
+ single: \ch{CH3-CH3} \par
+ double: \ch{CH2=CH2} \par
+ triple: \ch{CH+CH}
+\end{example}
+
+\subsubsection{Flexible Bonds}
+\paragraph{Predefined Bonds}
+In addition to the three native bonds there are a few more which can be called
+by
+\begin{commands}
+ \command{bond}[\marg{bond name}]
+ Prints the bond type specified by \meta{bond name}.
+\end{commands}
+The predefined bond types are shown in table~\vref{tab:bond_types}.
+
+\begin{table}
+ \centering
+ \caption{Bonds available with \cs*{bond}.}
+ \label{tab:bond_types}
+ \begin{tabular}{lcl}
+ \toprule
+ \bfseries name & \bfseries appearance & \bfseries aliases \\
+ \midrule
+ \code{single} & \bond{single} & \code{normal}, \code{sb} \\
+ \code{double} & \bond{double} & \code{db} \\
+ \code{triple} & \bond{triple} & \code{tp} \\
+ \code{dotted} & \bond{dotted} & \code{semisingle} \\
+ \code{deloc} & \bond{deloc} & \code{semidouble} \\
+ \code{tdeloc} & \bond{tdeloc} & \code{semitriple} \\
+ \code{co>} & \bond{co>} & \code{coordright} \\
+ \code{<co} & \bond{<co} & \code{coordleft} \\
+ \bottomrule
+ \end{tabular}
+\end{table}
+
+\begin{example}
+ \ch{C\bond{sb}C\bond{db}C\bond{tp}C\bond{deloc}C\bond{tdeloc}C\bond{co>}C\bond{<co}C}
+\end{example}
+
+\paragraph{Own Bonds}
+\chemformula{} offers commands to define own bond types:
+\begin{commands}
+ \command{NewChemBond}[\marg{name}\marg{code}]
+ \sinceversion{4.3}Define the new bond type \meta{name}. Issue an error if
+ a bond \meta{name} already exists.
+ \command{DeclareChemBond}[\marg{name}\marg{code}]
+ Define the new bond type \meta{name} or overwrite it if it already
+ exists.
+ \command{RenewChemBond}[\marg{name}\marg{code}]
+ Redefine the existing bond type \meta{name}. Issue an error if a bond
+ \meta{name} doesn't exist.
+ \command{ProvideChemBond}[\marg{name}\marg{code}]
+ \sinceversion{4.12a}Define the new bond type \meta{name} only if it
+ doesn't exist yet.
+ \command{NewChemBondAlias}[\marg{new name}\marg{old name}]
+ \sinceversion{4.3}Declare the bond type \meta{new name} to be an alias of
+ \meta{old name}. Issue an error if a bond \meta{new name} already
+ exists.
+ \command{DeclareChemBondAlias}[\marg{new name}\marg{old name}]
+ Declare the bond type \meta{new name} to be an alias of \meta{old name}.
+ \command{ShowChemBond}[\marg{name}]
+ Print the definition of bond type \meta{name}.
+\end{commands}
+The usage is best described with an example. So let's see how the
+\code{single} bond and the \code{co>} bond are defined:
+\begin{sourcecode}
+ \NewChemBond{single}
+ { \draw[chembond] (chemformula-bond-start) -- (chemformula-bond-end) ; }
+ \NewChemBond{coordright}
+ {
+ \draw[chembond,butt cap->]
+ (chemformula-bond-start) -- (chemformula-bond-end) ;
+ }
+ \NewChemBondAlias{co>}{coordright}
+\end{sourcecode}
+Two points are important: the names of the starting and the ending
+coordinates, \code{chemformula-bond-start} and \code{chemformula-bond-end},
+and the \TikZ\ style of the bonds \code{chembond}.
+
+So, let's say you want to define a special kind of dashed bond. You could do
+this:
+\begin{example}
+ \usetikzlibrary{decorations.pathreplacing}
+ \makeatletter
+ \NewChemBond{dashed}
+ {
+ \draw[
+ chembond,
+ decorate,
+ decoration={
+ ticks,
+ segment length=\chemformula@bondlength/10,amplitude=1.5pt
+ }]
+ (chemformula-bond-start) -- (chemformula-bond-end) ;
+ }
+ \makeatother
+ \setchemformula{bond-length=2ex}
+ \ch{C\bond{dashed}C}
+\end{example}
+
+The last example showed you another macro: \verbcode+\chemformula@bondlength+.
+It only exists so you can use it to access the bond length as set with
+\option{bond-length} directly.
+
+\subsection{Customization}\label{ssec:compounds:customization}
+These options allow you to customize the ouptut of the compounds:
+\begin{options}
+ \keyval{subscript-vshift}{dim}\Default{0pt}
+ Extra vertical shift of the subscripts.
+ \keychoice{subscript-style}{text,math}\Default{text}
+ Style that is used to typeset the subscripts.
+ \keyval{charge-hshift}{dim}\Default{.25em}
+ Shift of superscripts when following a subscript.\label{desc:charge-hshift}
+ \keyval{charge-vshift}{dim}\Default{0pt}
+ Extra vertical shift of the superscripts.
+ \keychoice{charge-style}{text,math}\Default{text}
+ Style that is used to typeset the superscripts.
+ \keychoice{circled}{formal,\default{all},none}\Default{formal}
+ \sinceversion{4.6}Like \chemmacros' package option but local to
+ \chemformula's \cs{ch}. That is: since \chemmacros' macros use
+ \chemformula's mechanism this is effectively an alias.
+ \keychoice{circletype}{\default{chem},math}\Default{chem}
+ \sinceversion{4.6}Like \chemmacros' package option but local to
+ \chemformula's \cs{ch}. That is: since \chemmacros' macros use
+ \chemformula's mechanism this is effectively an alias.
+ \keyval{adduct-space}{dim}\Default{.1333em}
+ Space to the left and the right of the adduct point.
+ \keyval{adduct-penalty}{num}\Default{300}
+ The\sinceversion{4.14} penalty inserted after the adduct point for
+ (dis-)allowing line breaks.
+ \keyval{bond-length}{dim}\Default{.5833em}
+ The length of the bonds.
+ \keyval{bond-offset}{dim}\Default{.07em}
+ Space between bond and atoms.
+ \keyval{bond-style}{\TikZ}\Default
+ \TikZ\ options for the bonds.
+ \keyval{bond-penalty}{num}\Default{10000}
+ \sinceversion{4.0a}The penalty that is inserted after a bond for
+ (dis-)allowing line breaks.
+ \keyval{radical-style}{\TikZ}\Default
+ \TikZ\ options for the radical point.
+ \keyval{radical-radius}{dim}\Default{.2ex}
+ The radius of the radical point.
+ \keyval{radical-hshift}{dim}\Default{.15em}
+ Horizontal shift before the radical point is drawn.
+ \keyval{radical-vshift}{dim}\Default{.5ex}
+ Vertical shift relative to the current baseline.
+ \keyval{radical-space}{dim}\Default{.15em}
+ Horizontal shift after the radical point is drawn.
+\end{options}
+
+Maybe you have noticed that charges of certain ions are shifted to the
+right.
+\begin{example}[side-by-side]
+ \ch{SO4^2-} \ch{NH4+} \ch{Na+}
+\end{example}
+They are shifted if they \emph{follow} a subscript which follows \ac{iupac}
+recommendations~\cite[][p.\,51]{iupac:greenbook}. The amount of the shift can
+be set with the option \option{charge-hshift}.
+\begin{example}
+ \ch{SO4^2-} \ch{NH4+} \ch{Na+} \par
+ \setchemformula{charge-hshift=.5ex}
+ \ch{SO4^2-} \ch{NH4+} \ch{Na+} \par
+ \setchemformula{charge-hshift=.5pt}
+ \ch{SO4^2-} \ch{NH4+} \ch{Na+}
+\end{example}
+
+Despite \ac{iupac}'s recommendation \chemformula\ does not make fully staggered
+arrangements in the default setting as I find it hard to read in some cases
+and ugly in others. Since this is a subjective decision \chemformula\ not only
+let's you define the absolute amount of the shift but also provides a
+possibility for full staggered arrangements. For this you have to use
+\keyis{charge-hshift}{full}.
+\begin{example}
+ \ch[charge-hshift=0pt]{C5H11+} \ch[charge-hshift=0pt]{SO4^2-} \par
+ \ch{C5H11+} \ch{SO4^2-} \par
+ \ch[charge-hshift=1ex]{C5H11+} \ch[charge-hshift=1ex]{SO4^2-} \par
+ \ch[charge-hshift=full]{C5H11+} \ch[charge-hshift=full]{SO4^2-}
+\end{example}
+
+If you don't want the charges to be typeset in text mode you can switch to
+math mode:
+\begin{example}
+ \ch{M^x+} \ch{SO4^2-} \par
+ \setchemformula{charge-style = math}
+ \ch{M^x+} \ch{SO4^2-}
+\end{example}
+
+The option \option{subscript-vshift} can be used to adjust the vertical shift
+of the subscripts:
+\begin{example}
+ \ch{H2SO4} \ch{Na3PO4} \par
+ \setchemformula{subscript-vshift=.5ex}
+ \ch{H2SO4} \ch{Na3PO4} \par
+ \setchemformula{subscript-vshift=-.2ex}
+ \ch{H2SO4} \ch{Na3PO4}
+\end{example}
+
+You can choose the mode subscripts are typeset in the same way as it is
+possible for the charges:
+\begin{example}
+ \ch{A_nB_m} \ch{H2SO4} \par
+ \setchemformula{subscript-style = math}
+ \ch{A_nB_m} \ch{H2SO4}
+\end{example}
+
+The option \option{adduct-space} sets the space left and right to the adduct
+symbol $\cdot$.
+\begin{example}
+ \ch{Na3PO3*H2O} \par
+ \setchemformula{adduct-space=.2em}
+ \ch{Na3PO3*H2O}
+\end{example}
+
+Changing the length of the bonds:
+\begin{example}
+ \setchemformula{bond-length=4mm}%
+ single: \ch{CH3-CH3} \par
+ double: \ch{CH2=CH2} \par
+ triple: \ch{CH+CH}
+\end{example}
+
+You can change the distance between bond and atom, too:
+\begin{example}
+ \ch{H-H + N+N + O=O} \par
+ \ch[bond-offset=1pt]{H-H + N+N + O=O}
+\end{example}
+
+\subsection{Standalone Formulae}
+\chemformula\sinceversion{4.0} offers a command that \emph{only accepts} the
+\enquote{compound} input type:
+\begin{commands}
+ \command{chcpd}[\oarg{options}\marg{compound}]
+ Typeset single compounds.
+\end{commands}
+
+\subsection{Extend Compound Properties}\label{sec:extend-comp-prop}
+
+It\sinceversion{4.10} is possible to extend the range of special input symbols
+within compounds. In the default setting those are \verbcode|*.-=+'| and
+arabic numerals. Others can be added or the existing ones be changed with one
+of the following commmands:
+\begin{commands}
+ \command{NewChemCompoundProperty}[\marg{token}\marg{replacement}]
+ \meta{token} will be replaced by \meta{replacement} within compounds. The
+ property is only added if \meta{token} is not yet part the compounds'
+ property list. Otherwise an error is issued.
+ \command{ProvideChemCompoundProperty}[\marg{token}\marg{replacement}]
+ \meta{token}\sinceversion{4.12a} will be replaced by \meta{replacement}
+ within compounds. The property is only added if \meta{token} is not yet
+ part the compounds' property list.
+ \command{RenewChemCompoundProperty}[\marg{token}\marg{replacement}]
+ \meta{token} will be replaced by \meta{replacement} within compounds. The
+ property is only added if \meta{token} is already part the compounds'
+ property list. Otherwise an error is issued.
+ \command{DeclareChemCompoundProperty}[\marg{token}\marg{replacement}]
+ \meta{token} will be replaced by \meta{replacement} within compounds. The
+ property silently overwrites any previously set \meta{replacement} for
+ \meta{token} if \meta{token} is already part the compounds' property
+ list.
+ \command{RemoveChemCompoundProperty}[\marg{token}]
+ Removes \meta{token} from the compounds' property list.
+\end{commands}
+
+For example you can use
+\begin{sourcecode}
+ \NewChemCompoundProperty{\}{\slash}
+\end{sourcecode}
+to allow line breaks after slashes in compounds.
+
+\section{Special Input Types}
+There are some \enquote{special type} input groups.
+
+\subsection{Single Token Groups}
+The first kind are groups which consist of only one token. They are again
+divided into two groups, \enquote{addition symbols} and \enquote{symbols}.
+
+\subsubsection{Addition Symbols}\label{sec:addition-symbols}
+\begin{commands}
+ \command{ch}[\Marg{ + } \ch{ + }]
+ Creates the plus sign between compounds with space around it:\\
+ \cs{ch}\Marg{2 Na + Cl2} \ch{2 Na + Cl2}
+ \command{ch}[\Marg{ - } \ch{ - }]
+ \sinceversion{4.3a}Creates the minus sign between compounds with space
+ around it:\\
+ \cs{ch}\Marg{M - H} \ch{M - H}
+\end{commands}
+Addition symbols are surrounded with space which can be customized according
+to options explained in a bit. There is also some penalty prohibiting a line
+break after them which also can be customized with an option.
+
+You can define/redefine your own addition symbols:
+\begin{commands}
+ \command{NewChemAdditionSymbol}[\marg{name}\marg{input}\marg{output}]
+ Defines\sinceversion{4.11} the addition symbol \meta{name} with input
+ symbol \meta{input} and output \meta{output}.
+ \command{ProvideChemAdditionSymbol}[\marg{name}\marg{input}\marg{output}]
+ Defines\sinceversion{4.12a} the addition symbol \meta{name} with input
+ symbol \meta{input} and output \meta{output} only no addition symbol with
+ then name \meta{name} doesn't exist.
+ \command{RenewChemAdditionSymbol}[\marg{name}\marg{input}\marg{output}]
+ Redefines\sinceversion{4.11} the addition symbol \meta{name} with input
+ symbol \meta{input} and output \meta{output}.
+ \command{DeclareChemAdditionSymbol}[\marg{name}\marg{input}\marg{output}]
+ (Re-)Defines\sinceversion{4.11} the addition symbol \meta{name} with input
+ symbol \meta{input} and output \meta{output} without checking if the
+ symbol exists or not.
+\end{commands}
+
+The space left and right of the plus and the minus sign and the signs
+themselves can be set with the following options:
+\begin{options}
+ \keyval{plus-space}{skip}\Default{.3em plus .1em minus .1em}
+ A rubber length.
+ \keyval{plus-penalty}{num}\Default{700}
+ \sinceversion{4.0a}The penalty that is inserted after the plus sign for
+ (dis-)allowing line breaks.
+ \keyval{plus-output-symbol}{code}\Default{+}
+ \sinceversion{4.9}The \meta{code} that is used for the plus sign.
+ \keyval{minus-space}{skip}\Default{.3em plus .1em minus .1em}
+ \sinceversion{4.9}A rubber length.
+ \keyval{minus-penalty}{num}\Default{700}
+ \sinceversion{4.9}The penalty that is inserted after the minus sign for
+ (dis-)allowing line breaks.
+ \keyval{minus-output-symbol}{code}\Default{\$-\$}
+ \sinceversion{4.9}The \meta{code} that is used for the minus sign.
+\end{options}
+The corresponding three options are defined when \cs{NewChemAdditionSymbol}
+or one of the variants is used, \code{\meta{name}-space} and
+\code{\meta{name}-penalty} both with the same defaults as above, and
+\code{\meta{name}-output-symbol}.
+
+\begin{example}[side-by-side]
+ \ch{A + B}\par
+ \ch[plus-space=4pt]{A + B}
+\end{example}
+
+\subsubsection{Symbols}\label{sec:symbols}
+\begin{commands}
+ \command{ch}[\Marg{ v } \ch{ v }]
+ Sign for precipitate: \cs{ch}\Marg{BaSO4 v} \ch{BaSO4 v}
+ \command{ch}[\Marg{ \textasciicircum\ } \ch{ ^ }]
+ Sign for escaping gas\footnotemark: \cs{ch}\Marg{H2 \textasciicircum}
+ \ch{H2 ^}
+\end{commands}
+\footnotetext{Is this the correct English term? Please correct me if it isn't.}
+
+You can define/redefine your own symbols:
+\begin{commands}
+ \command{NewChemSymbol}[\marg{input}\marg{output}]
+ Defines\sinceversion{4.11} the addition symbol with input \meta{input} and
+ output \meta{output}.
+ \command{ProvideChemSymbol}[\marg{input}\marg{output}]
+ Defines\sinceversion{4.12a} the addition symbol with input \meta{input} and
+ output \meta{output} only if no symbol with input \meta{input} exists.
+ \command{RenewChemSymbol}[\marg{input}\marg{output}]
+ Redefines\sinceversion{4.11} the addition symbol with input \meta{input}
+ and output \meta{output}.
+ \command{DeclareChemSymbol}[\marg{input}\marg{output}]
+ (Re-)Defines\sinceversion{4.11} the addition symbol with input
+ \meta{input} and output \meta{output} without checking if the symbol
+ exists or not.
+\end{commands}
+
+\subsection{Option Input}
+Sometimes you might want to apply an option only to a part of a, say,
+reaction. Of course you have the possibility to use \cs{ch} several times.
+\begin{example}
+ \ch{H2O +}\textcolor{red}{\ch{H2SO4}}\ch{-> H3O+ + HSO4-} \par
+ \ch{H2O +}\ch[subscript-vshift=2pt]{H2SO4}\ch{-> H3O+ + HSO4-}
+\end{example}
+This, however, interrupts the input in your source and \emph{may} mess with
+the spacing. That's why there is an alternative:
+\begin{commands}
+ \command{ch}[\Marg{ @\marg{options} }]
+ The options specified this way will be valid \emph{only} until the next
+ compound is set.
+\end{commands}
+\begin{example}
+ \ch{H2O +}\textcolor{red}{\ch{H2SO4}}\ch{-> H3O+ + HSO4-} \par
+ \ch{H2O + @{format=\color{red}} H2SO4 -> H3O+ + HSO4-} \par
+ or of course:\par
+ \ch{H2O + \textcolor{red}{H2SO4} -> H3O+ + HSO4-}\par\bigskip
+ \ch{H2O +}\ch[subscript-vshift=2pt]{H2SO4}\ch{-> H3O+ + HSO4-} \par
+ \ch{H2O + @{subscript-vshift=2pt} H2SO4 -> H3O+ + HSO4-}
+\end{example}
+
+\section{Escaped Input}
+In some cases it may be desirable to prevent \chemformula\ from parsing the
+input. This can be done in two ways.
+
+\subsection{Text}\label{ssec:text}
+If you put something between \verbcode+" "+ or \verbcode+' '+ then the input
+will be treated as normal text, except that spaces are not allowed and have to
+be input with \verbcode+~+.
+\begin{commands}
+ \command{ch}[\Marg{ "\meta{escaped text}" }]
+ One of two possibilities to \emph{escape} \chemformula's parsing.
+ \command{ch}[\Marg{ \textquotesingle\meta{escaped text}\textquotesingle\ }]
+ The second of two possibilities to \emph{escape} \chemformula's parsing.
+\end{commands}
+\begin{example}[add-sourcecode-options={literate=}]
+ \ch{"\ox{2,Ca}" O} \par
+ \ch{"\ldots\," Na + "\ldots\," Cl2 -> "\ldots\," NaCl} \par
+ \ch{'A~->~B'}
+\end{example}
+In many cases you won't need to escape the input. But when you get into
+trouble when using a command inside \cs{ch} try hiding it.
+
+\subsection{Math}
+If you especially want to input math you just enclose it with \verbcode+$ $+.
+This output is different from the escaped text as it is followed by a space.
+The reasoning behind this is that I assume math will mostly be used to replace
+stoichiometric factors.
+\begin{commands}
+ \command{ch}[\Marg{ \string$\meta{escaped math}\string$ }]
+ One of two possibilities to \emph{escape} \chemformula's parsing into math
+ mode.
+ \command{ch}[\Marg{ \string\(\meta{escaped math}\string\) }]
+ The second of two possibilities to \emph{escape} \chemformula's parsing
+ into math mode.
+\end{commands}
+\begin{example}[side-by-side]
+ escaped text: \ch{"$x$" H2O} \par
+ escaped math: \ch{$x$ H2O} \par
+ also escaped math: \ch{\(x\) H2O} \par
+ \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl}
+\end{example}
+
+The space that is inserted after a math group can be edited:
+\begin{options}
+ \keyval{math-space}{skip}\Default{.1667em plus .0333em minus .0117em}
+ A rubber length.
+\end{options}
+\begin{example}
+ \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl} \par
+ \setchemformula{math-space=.25em}
+ \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl} \par
+ \ch{$A->B$}
+\end{example}
+
+\section{Arrows}\label{sec:arrows}
+\subsection{Arrow types}
+Arrows are input in the same intuitive way they are with \pkg{mhchem}.
+There are various different types:
+\begin{arrows}
+ \arrow{->}[ \charrow{->}]
+ standard right arrow
+ \arrow{<-}[ \charrow{<-}]
+ standard left arrow
+ \arrow{-/>}[ \charrow{-/>}]
+ does not react (right)
+ \arrow{</-}[ \charrow{</-}]
+ does not react (left)
+ \arrow{<->}[ \charrow{<->}]
+ resonance arrow
+ \arrow{<>}[ \charrow{<>}]
+ reaction in both directions
+ \arrow{==}[ \charrow{==}]
+ stoichiometric equation
+ \arrow{<=>}[ \charrow{<=>}]
+ equilibrium arrow
+ \arrow{>=<}[ \charrow{>=<}]
+ \sinceversion{4.5}reversed equilibrium arrow
+ \arrow{<=>{}>}[ \charrow{<=>>}]
+ unbalanced equilibrium arrow to the right
+ \arrow{>=<{}<}[ \charrow{>=<<}]
+ \sinceversion{4.5}reversed unbalanced equilibrium arrow to the right
+ \arrow{<{}<=>}[ \charrow{<<=>}]
+ unbalanced equilibrium arrow to the left
+ \arrow{>{}>=<}[ \charrow{>>=<}]
+ \sinceversion{4.5}reversed unbalanced equilibrium arrow to the left
+ \arrow{<=o>}[ \charrow{<=o>}]
+ \sinceversion{4.15}quasi equilibrium arrow
+ \arrow{<=o>{}>}[ \charrow{<=o>>}]
+ \sinceversion{4.15}unbalanced quasi equilibrium arrow to the right
+ \arrow{<{}<=o>}[ \charrow{<<=o>}]
+ \sinceversion{4.15}unbalanced quasi equilibrium arrow to the left
+ \arrow{<o>}[ \charrow{<o>}]
+ isolobal arrow
+ \arrow{<==>}[ \charrow{<==>}]
+ \sinceversion{4.5}I've seen this one used. I'm not sure it actually has a
+ meaning in chemical equations. If you have some official reference for
+ this arrow type please feel free to contact me.
+\end{arrows}
+All these arrows are drawn with \TikZ.
+\begin{example}
+ \ch{H2 + Cl2 -> 2 HCl} \par
+ \ch{H2O + CO3^2- <=> OH- + HCO3-} \par
+ \ch{A <- B} \par
+ \ch{\{[CH2=CH-CH2]- <-> {}[CH2-CH=CH2]- \}} \par
+ \ch{A <> B} \par
+ \ch{H+ + OH- <=>> H2O} \par
+ \ch{2 NO2 <<=> N2O4}
+\end{example}
+
+\subsection{Labels}
+The arrows take two optional arguments to label them.
+\begin{arrows}
+ \arrow*{->\oarg{above}\oarg{below}}
+ Add text above or under an arrow.
+\end{arrows}
+\begin{example}[side-by-side]
+ \ch{A ->[a] B} \par
+ \ch{A ->[a][b] B} \par
+ \ch{A ->[\SI{100}{\celsius}] B}
+\end{example}
+The label text can be parsed seperately from the arrow. The recipe is easy:
+leave blanks.
+\begin{example}[side-by-side]
+ \ch{A ->[H2O] B} \par
+ \ch{A ->[ H2O ] B} \par
+ \ch{A ->[ "\ox{2,Ca}" F2 ] B} \par
+ \ch{A ->[ $\Delta$,~ [ H+ ]] B}
+\end{example}
+
+If you leave the blanks \chemformula\ treats the groups inside the square
+brackets as seperated input types. The arrow reads its arguments
+\emph{afterwards}. As you can see the arrows \enquote{grow} with the length
+of the labels. What stays constant is the part that protrudes the labels.
+\begin{example}
+ \ch{A ->[a] B} \par
+ \ch{A ->[ab] B} \par
+ \ch{A ->[abc] B} \par
+ \ch{A ->[abc~abc] B} \par
+ % needs the `chemfig' package:
+ \setchemfig{atom sep =15pt}
+ \ch{A ->[ "\chemfig{-[:30]-[:-30]OH}" ] B} \par
+\end{example}
+
+\subsection{Customization}
+These are the options which enable you to customize the arrows:
+\begin{options}
+ \keyval{arrow-offset}{dim}\Default{.75em}
+ This is the length that an arrow protrudes a label on both sides. This
+ means an empty arrow's length is two times \code{arrow-offset}.
+ \keyval{arrow-min-length}{dim}\Default{0pt}
+ \sinceversion{3.6b}The minimal length an error must have unless two times
+ \option{arrow-offset} plus the width of the label is larger.
+ \keyval{arrow-yshift}{dim}\Default{0pt}
+ Shifts an arrow up (positive value) or down (negative value).
+ \keyval{arrow-ratio}{<factor>}\Default{.6}
+ The ratio of the arrow lengths of the unbalanced equilibrium. \code{.4}
+ would mean that the length of the shorter arrow is $0.4\times$ the length
+ of the longer arrow.
+ \keyval{compound-sep}{dim}\Default{.5em}
+ The space between compounds and the arrows.
+ \keyval{label-offset}{dim}\Default{2pt}
+ The space between the labels and the arrows.
+ \keyval{label-style}{font command}\Default{\cs*{footnotesize}}
+ The relative font size of the labels.
+ \keyval{arrow-penalty}{num}\Default{0}
+ \sinceversion{4.0a}The penalty that is inserted after an arrow for
+ (dis-)allowing line breaks.
+ \keyval{arrow-style}{\TikZ}\Default
+ \sinceversion{4.1a}Additonal \TikZ\ keys for formatting the arrows.
+\end{options}
+
+The following code shows the effect of the different options on the \verbcode+<=>>+
+arrow:
+\begin{example}
+ standard: \ch{A <=>>[x][y] B} \par
+ longer: \ch[arrow-offset=12pt]{A <=>>[x][y] B} \par
+ higher: \ch[arrow-yshift=2pt]{A <=>>[x][y] B} \par
+ more balanced: \ch[arrow-ratio=.8]{A <=>>[x][y] B} \par
+ labels further away: \ch[label-offset=4pt]{A <=>>[x][y] B} \par
+ larger distance to compounds: \ch[compound-sep=2ex]{A <=>>[x][y] B} \par
+ smaller labels: \ch[label-style=\tiny]{A <=>[x][y] B}
+\end{example}
+
+If you want to have different arrow tips\sinceversion{4.7} there is an easy
+way to use existing arrow tips (as defined by \TikZ). \chemformula\ uses
+three different arrow tips: \code{cf}, \code{left cf} and \code{right cf}. If
+you want them to match those of \pkg{chemfig}~\cite{pkg:chemfig} for example
+you could do:
+\begin{sourcecode}
+ \pgfkeys{
+ cf /.tip = {CF@full} ,
+ left cf /.tip = {CF@half}
+ }
+\end{sourcecode}
+\pkg{chemfig} has no equivalent of \code{right cf}. This mechanism relies on
+\TikZ\ version~3.0.0 and the new \code{arrows.meta} library.
+
+\subsection{Modify Arrow Types}\label{sec:arrows_modify}
+The arrows are defined with the commands
+\begin{commands}
+ \command{NewChemArrow}[\marg{type}\marg{\TikZ}]
+ Define the new arrow type \meta{type}. Issue an error if an arrow type
+ \meta{type} already exists.
+ \command{ProvideChemArrow}[\marg{type}\marg{\TikZ}]
+ Define\sinceversion{4.12a} the new arrow type \meta{type} only if it
+ doesn't exist, yet.
+ \command{DeclareChemArrow}[\marg{type}\marg{\TikZ}]
+ Define the new arrow type \meta{type} or overwrite it if it already
+ exists.
+ \command{RenewChemArrow}[\marg{type}\marg{\TikZ}]
+ Redefine the arrow type \meta{type}. Issue an error if an arrow type
+ \meta{type} doesn't exist.
+ \command{ShowChemArrow}[\marg{type}]
+ Print out the current definition of the arrow type \meta{type}.
+\end{commands}
+\meta{type} is the sequence of tokens that is replaced with the actual arrow
+code. For example the basic arrow is defined via
+\begin{sourcecode}
+ \NewChemArrow{->}{
+ \draw[chemarrow,-cf] (cf_arrow_start) -- (cf_arrow_end) ;
+ }
+\end{sourcecode}
+In order to define arrows yourself you need to know the basics of
+\TikZ\footnote{Please see the \manual{pgfmanual} for details.}. The
+predefined arrows use the arrow tips \code{cf}, \code{left cf} and \code{right
+ cf}. They also all except the net reaction arrow \code{==} use the
+\TikZ-style \code{chemarrow} that you should use, too, if you want the option
+\option{arrow-style} to have an effect.
+
+There are some predefined coordinates you can and should use. For
+completeness' sake the arrow tips and the \TikZ-style are also listed:
+\begin{codedesc}
+ \Code{(cf\_arrow\_start)}
+ The beginning of the arrow.
+ \Code{(cf\_arrow\_end)}
+ The end of the arrow.
+ \Code{(cf\_arrow\_mid)}
+ The mid of the arrow.
+ \Code{(cf\_arrow\_mid\_start)}
+ The beginning of the shorter arrow in types like \verbcode+<=>>+.
+ \Code{(cf\_arrow\_mid\_end)}
+ The end of the shorter arrow in types like \verbcode+<=>>+.
+ \Code{cf}
+ A double-sided arrow tip.
+ \Code{left cf}
+ A left-sided arrow tip.
+ \Code{right cf}
+ A right-sided arrow tip.
+ \Code{chemarrow}
+ \chemformula's \TikZ-style that is applied to the arrows and set with
+ \option{arrow-style}
+\end{codedesc}
+\begin{example}
+ \NewChemArrow{.>}{
+ \draw[chemarrow,-cf,dotted,red] (cf_arrow_start) -- (cf_arrow_end);
+ }
+ \NewChemArrow{n>}{
+ \draw[chemarrow,-cf]
+ (cf_arrow_start)
+ .. controls ([yshift=3ex]cf_arrow_mid) ..
+ (cf_arrow_end);
+ }
+ \ch{A .> B} \ch{A .>[a][b] B} \ch{A n> B}
+\end{example}
+
+\begin{example}
+ \texttt{\ShowChemArrow{->}} \par
+ \RenewChemArrow{->}{\draw[chemarrow,->,red] (cf_arrow_start) -- (cf_arrow_end) ;}
+ \texttt{\ShowChemArrow{->}} \par
+ \ch{A -> B}
+\end{example}
+
+\subsection{Standalone Arrows}
+\chemformula\ offers\sinceversion{4.0} a command that \emph{only accepts} the
+\enquote{arrow} input type:
+\begin{commands}
+ \command{charrow}[\marg{type}\oarg{above}\oarg{below}]
+ Print the arrow type \meta{type}.
+\end{commands}
+This command is internally used for the arrows, too, when \cs{ch} is parsed.
+
+\section{Names}
+\subsection{Syntax}
+\chemformula\ has a built-in syntax to write text under a compound. In a way
+it works very similar to the arrows.
+\begin{commands}
+ \command{ch}[\Marg{ !(\meta{text})( \meta{formula} ) }]
+ Writes \meta{text} below \meta{formula}.
+\end{commands}
+If an exclamation mark is followed by a pair of parentheses \chemformula\ will
+parse it this way:
+\begin{example}
+ \ch{!(ethanol)( CH3CH2OH )}
+\end{example}
+The same what's true for the arrows arguments holds for these arguments: if
+you leave blanks the different parts will be treated according to their input
+type before the text is set below the formula.
+\begin{example}
+ \ch{!(water)(H2O)} \quad
+ \ch{!( "\textcolor{blue}{water}" )( H2O )} \quad
+ \ch{!( $2n-1$ )( H2O )} \quad
+ \ch{!( H2O )( H2O )} \quad
+ \ch{!(oxonium)( H3O+ )}
+\end{example}
+If for some reason you want to insert an exclamation mark \emph{without} it
+creating a name you only have to make sure it isn't followed by parentheses.
+\begin{example}[side-by-side]
+ \ch{H2O~(!)} \par
+ \ch{A!{}()}
+\end{example}
+
+\subsection{Customization}
+\chemformula\ provides two options to customize the output of the names:
+\begin{options}
+ \keyval{name-format}{commands}\Default{\cs*{scriptsize}\cs*{centering}}
+ The format of the name. This can be arbitrary input.
+ \keychoice{name-width}{\meta{dim},auto}\Default{auto}
+ The width of the box where the label is put into. \code{auto} will detect
+ the width of the name and set the box to this width.
+\end{options}
+\begin{example}
+ \ch{!(acid)( H2SO4 ) -> B} \par
+ \ch[name-format=\sffamily\small]{!(acid)( H2SO4 ) -> B} \par
+ \ch[name-format=\scriptsize N:~]{!(acid)( H2SO4 ) -> B} \par
+ \ch[name-width=3em,name-format=\scriptsize\raggedright]{!(acid)( H2SO4 ) -> B}
+\end{example}
+
+\subsection{Standalone Names}
+\chemformula\ offers a command\sinceversion{4.0} that allows the usage of the
+\enquote{name} syntax in normal text. This is the command that a bang is
+replaced with in \chemformula's formulas, actually. Both arguments are
+mandatory.
+\begin{commands}
+ \command{chname}[\darg{text~1}\darg{text~2}]
+ The command that is useed internally for placing \meta{text~1} below of
+ \meta{text~2}.
+\end{commands}
+
+\section{Format and Font}\label{sec:format}
+In the standard setting \chemformula\ doesn't make any default changes to the
+font of the formula output. Let's take a look at a nonsense input which shows
+all features:
+\begin{example}[pre-output={\biolinumLF\libertineLF\setchemformula{format=}}]
+ \newcommand*\sample{%
+ \ch{H2C-C+C-CH=CH+ + CrO4^2-
+ <=>[x][y]
+ 2.5 Cl^{-.} + 3_1/2 Na*OH_{(aq)} + !(name)( A^n ) "\LaTeXe"}
+ }
+ \sample
+\end{example}
+\newcommand*\sample{%
+ \ch{H2C-C+C-CH=CH+ + CrO4^2-
+ <=>[x][y]
+ 2.5 Cl^{-.} + 3_1/2 Na*OH_{(aq)} + !(name)( A^n ) "\LaTeXe"}
+}
+
+Now we're going to change different aspects of the font a look what happens:
+\begin{example}[pre-output={\biolinumLF\libertineLF\setchemformula{format=}}]
+ \sffamily Hallo \sample \\
+ \ttfamily Hallo \sample \normalfont \\
+ \bfseries Hallo \sample \normalfont \\
+ \itshape Hallo \sample
+\end{example}
+As you can see most features adapt to the surrounding font.
+
+If you want to change the default format you need to use this option:
+\begin{options}
+ \keyval{format}{code}\Default
+ Adds \meta{code} before the output of \cs{ch}.
+ \keyval{atom-format}{code}\Default
+ This\sinceversion{4.13} adds \meta{code} before each formula. This
+ allows to specify a format for the chemical formulas only and have a
+ different format for the rest of the chemical equation.
+\end{options}
+\begin{example}[pre-output={\biolinumLF\libertineLF\setchemformula{format=}}]
+ \definecolor{newblue}{rgb}{.1,.1,.5}
+ \setchemformula{format=\color{newblue}\sffamily}
+ \sffamily Hallo \sample \\
+ \ttfamily Hallo \sample \normalfont \\
+ \bfseries Hallo \sample \normalfont \\
+ \itshape Hallo \sample
+\end{example}
+
+You can also specifically change the fontfamily, fontseries and fontshape of
+the output.
+\begin{options}
+ \keyval{font-family}{family}\Default
+ Changes the fontfamily of the output with \cs*{fontfamily}\marg{family}.
+ \keyval{font-series}{series}\Default
+ Changes the fontseries of the output with \cs*{fontseries}\marg{series}.
+ \keyval{font-shape}{shape}\Default
+ Changes the fontshape of the output with \cs*{fontshape}\marg{shape}.
+\end{options}
+\begin{example}[pre-output={\biolinumLF\libertineLF\setchemformula{format=}}]
+ \setchemformula{font-series=bx}
+ Hallo \sample \par
+ \sffamily Hallo \sample \normalfont \par
+ \setchemformula{font-family=lmss,font-series=m} Hallo \sample
+ \normalfont \par
+ \itshape Hallo \sample
+\end{example}
+
+If you're using \XeLaTeX\ or \LuaLaTeX\ and have loaded \pkg{fontspec} you
+have the possibilty to set the font with it:
+\begin{options}
+ \keyval{font-spec}{font}\Default
+ Use font \meta{font} for \chemformula's formulas.
+\end{options}
+or with options
+\begin{options}
+ \keychoice{font-spec}{\Marg{[\meta{options}]\meta{font}}}
+ Use font \meta{font} with options \meta{options} for \chemformula's
+ formulas.
+\end{options}
+Since this document is typeset with \pdfLaTeX\ the option cannot be
+demonstrated here.
+
+\section{Usage In Math Equations}
+The \cs{ch} command can be used inside math equations. It recognizes
+\verbcode+\\+ and \verbcode+&+ and passes them on. However, you can't use the
+optional arguments of \verbcode+\\+ inside \cs{ch}.
+\begin{example}
+ \begin{align}
+ \ch{
+ H2O & ->[a] H2SO4 \\
+ Cl2 & ->[x][y] CH4
+ }
+ \end{align}
+ \begin{align*}
+ \ch{
+ RNO2 &<=>[ + e- ] RNO2^{-.} \\
+ RNO2^{-.} &<=>[ + e- ] RNO2^2-
+ }
+ \end{align*}
+\end{example}
+
+\section{Usage with \TikZ\ or \pkg*{pgfplots} and externalization}
+Since \chemformula\ uses\sinceversion{4.1} \TikZ\ to draw reaction arrows
+and bonds they would be externalized, too, if you use that facility with
+\TikZ\ or \needpackage{pgfplots}~\cite{pkg:pgfplots}. This may not be
+desirable since they are very small pictures maybe containing of a single
+line. This is why \chemformula's default behaviour is to disable
+externalization for it's bonds and arrows. This can be turned on and off
+through the following option:
+\begin{options}
+ \keybool{tikz-external-disable}\Default{true}
+ dis- or enable \TikZ' externalization mechanism for \chemformula's arrows
+ and bonds.
+\end{options}
+
+If you should be using a formula that contains bonds or arrows inside of a
+\code{tikzpicture} that is externalized you should locally enable it for
+\chemformula, too:
+
+\begin{sourcecode}
+ \begin{tikzpicture}
+ \setchemformula{tikz-external-disable=false}
+ \begin{axis}[xlabel={\ch{2 H+ + 2 e- -> H2}}]
+ \addplot ... ;
+ \end{axis}
+ \end{tikzpicture}
+\end{sourcecode}
+
+\section{Lewis Formulae}\label{sec:lewis-formulae}
+\chemformula\ offers\sinceversion{4.2} a command to typeset Lewis formulae.
+This does not mean Lewis structures! Those can be achieved using the
+\pkg{chemfig} package~\cite{pkg:chemfig}. \chemformula\ provides the
+possibility to draw electrons as dots and pairs of dots or a line around an
+atom.
+
+\begin{commands}
+ \command{chlewis}[\oarg{options}\marg{electron spec}\marg{atom}]
+ Draws electrons around the \meta{atom} according to \meta{electron spec}.
+\end{commands}
+
+Electrons are specified by the angle to the horizontal in the couter-clockwise
+direction. The default appearance is a pair of electrons drawn as a pair of
+dots. Other specifications can be chosen. The specification follows the
+pattern \meta{angle}\meta{separator}. \meta{angle} is a positiv or negativ
+integer denoting the angle counter clockwise to the horizontal where the
+electrons should be drawn. \meta{separator} is either a dot (\code{.}, single
+electron), a colon (\code{:}, electron pair), a vertical line (\code{|},
+electron pair), an o (\code{o}, empty pair), or a comma (\code{,} default
+spec).
+
+\begin{commands}
+ \command{chlewis}[\Marg{\meta{angle1}\meta{type1}\meta{angle2}\meta{type2}}%
+ \marg{atom}]
+ For example: \cs{chlewis}\Marg{0,180}\Marg{O} gives \chlewis{0,180}{O} and
+ \cs{chlewis}\Marg{0.90.180.270.}\Marg{C} gives
+ \chlewis{0.90.180.270.}{C}.
+\end{commands}
+
+The appearance can be influenced by a number of options:
+\begin{options}
+ \keychoice{lewis-default}{.,:,|,o,single,pair,pair (dotted),pair
+ (line),empty}\Default{pair}
+ Sets the default type that is used when no type is given in \meta{electron
+ spec}.
+ \keyval{lewis-distance}{dim}\Default{1ex}
+ The distance of two electrons in a pair.
+ \keyval{lewis-line-length}{dim}\Default{1.5ex}
+ The length of the line representing an electron pair.
+ \keyval{lewis-line-width}{dim}\Default{1pt}
+ The thickness of a line representing an electron pair.
+ \keyval{lewis-offset}{dim}\Default{.5ex}
+ The distance of the symbols from the atom.
+\end{options}
+The dots are drawn according to the \option{radical-radius} option mentioned
+in section~\ref{ssec:compounds:customization}.
+
+The basic usage should be more or less self-explaining:
+\begin{example}[side-by-side]
+ \chlewis{0:90|180.270}{O}
+ \quad
+ \chlewis{45,135}{O}
+ \quad
+ \chlewis{0o}{Na}
+\end{example}
+
+The next example shows the effect of some of the options:
+\begin{example}
+ \chlewis[lewis-default=.]{23,68,113,158,203,248,293,338}{X}
+ \quad
+ \chlewis{0,90,180,270}{X}
+ \quad
+ \chlewis[lewis-distance=1.25ex]{0,90,180,270}{X}
+ \quad
+ \chlewis[lewis-distance=.75ex,radical-radius=.5pt]{0,90,180,270}{X}
+ \quad
+ \chlewis[
+ radical-radius=.5pt,
+ lewis-default=.
+ ]{23,68,113,158,203,248,293,338}{X}
+\end{example}
+
+\begin{example}
+ \ch{
+ !($1s^22s^1$)( "\chlewis{180.}{Li}" ) +
+ !($1s^22s^22p^5$)( "\chlewis{0.90,180,270}{F}" )
+ ->
+ !($1s^2$)( Li+ ) + !($1s^22s^22p^6$)( "\chlewis{0,90,180,270}{F}" {}- )
+ }
+\end{example}
+
+\section{Kröger-Vink Notation}\label{sec:kroger-vink-notation}
+
+\chemformula\ also supports the Kröger-Vink notation\sinceversion{4.5}.
+\begin{options}
+ \keybool{kroeger-vink}\Default{false}
+ Enable the Kröger-Vink notation. As most options this can be enabled
+ globally via the setup command or locally as option to \cs{ch}.
+\end{options}
+
+With this option enabled several changes come into effect: \verbcode|'|
+produces a prime, a \code{x} in a superscript produces $\times$, and both a
+\code{.} and a \code{*} produce a little filled circle. In the Kröger-Vink
+notation a prime denotes a negative relative charge, the circle a positive
+relative charge, and the cross denotes a neutral relative charge.
+
+\begin{example}[side-by-side,add-sourcecode-options={literate=}]
+ \setchemformula{kroeger-vink=true}
+ \ch{Al_{Al}^'}
+ \ch{Al_{Al}'}\par
+ \ch{Ni_{Cu}^{x}}\par
+ \ch{V_{Cl}^.}
+ \ch{V_{Cl}^*}\par
+ \ch{Ca_i^{..}}\par
+ \ch{e^'}\par
+ \ch{Cl_i^'}
+ \ch{Cl_i'}\par
+ \ch{O_i^{''}}
+ \ch{O_i''}
+\end{example}
+
+There are a number of options for customizations:
+\begin{options}
+ \keyval{kv-positive-style}{\TikZ}\Default
+ \TikZ\ code for positive charge dot.
+ \keyval{kv-positive-radius}{dim}\Default{.3ex}
+ Radius of positive charge dot
+ \keyval{kv-positive-hshift}{dim}\Default{.15em}
+ Horizontal shift of positive charge dot
+ \keyval{kv-positive-vshift}{dim}\Default{.5ex}
+ Vertical shift positive charge dot
+ \keyval{kv-positive-offset}{dim}\Default{.4em}
+ The offset of two consecutive positive charge dots
+ \keyval{kv-neutral-symbol}{\TeX\ code}\Default{\$\cs*{times}\$}
+ Symbol for neutral particles.
+\end{options}
+
+\appendix
+\newenvironment{changes}[2][]{%
+ \subsection*{Version #2\ifblank{#1}{}{ (#1)}}
+ \itemize\let\change\item
+}{\enditemize}
+
+\section{History Since Version~4.0}
+
+\begin{changes}{4.0}
+ \change Since version 4.0\sinceversion{4.0}, the \chemformula\ package is
+ distributed independently from \chemmacros.
+\end{changes}
+
+\begin{changes}{4.1}
+ \change New option \option{tikz-external-disable}.
+ \change New option \option{frac-math-cmd}.
+\end{changes}
+
+\begin{changes}{4.2}
+ \change New option \option{arrow-style}.
+ \change New command \cs{chlewis} that allows to add Lewis electrons to an
+ atom, see section~\ref{sec:lewis-formulae}.
+\end{changes}
+
+\begin{changes}{4.3}
+ \change New option \option{stoich-print}.
+ \change New command \cs{chstoich}.
+ \change The commands \cs*{DeclareChem\meta{...}} now don't give an error any
+ more if the command already exists. This is more consistent with \LaTeX's
+ \cs*{DeclareRobustCommand}. For all those commands a version
+ \cs*{NewChem\meta{...}} is introduced that \emph{does} give an error if
+ the new command is already defined.
+\end{changes}
+
+\begin{changes}{4.4}
+ \change A single dash \code{-} in \cs{ch} is now treated as a minus sign.
+ This is consistent with the behaviour of a \code{+}.
+\end{changes}
+
+\begin{changes}{4.5}
+ \change New arrow types \arrowtype{>=<}, \arrowtype{>=<{}<}, \arrowtype{>{}>=<}
+ and \arrowtype{<==>}.
+ \change Internal changes to \cs{ch} allow usage of optional arguments of
+ \cs*{\textbackslash} and \cs*{label} in \chemmacros' \env*{reactions}
+ environment.
+\end{changes}
+
+\begin{changes}{4.6}
+ \change New options \option{circled} and \option{circletype}. this allows to
+ set the behaviour as described on \chemmacros' manual for a specific usage
+ of \cs{ch}.
+\end{changes}
+
+\begin{changes}{4.7}
+ \change Dependency change: \chemformula\ now requires the \TikZ\ library
+ \code{arrows.meta} instead of the library \code{arrows}. This requires
+ \TikZ\ version~3.0.0.
+\end{changes}
+
+\begin{changes}{4.8}
+ \change The \chemformula\ package now is no longer part of the \chemmacros\
+ bundle but is distributed as a package of it's own.
+\end{changes}
+
+\begin{changes}{4.9}
+ \change New options \option{minus-space} and \option{minus-penalty} equivalent
+ to the existing \option{plus-space} and \option{plus-penalty}
+ \change New options \option{plus-output-symbol} and
+ \option{minus-output-symbol} for customizing the plus and minus signs in
+ the output.
+\end{changes}
+
+\begin{changes}{4.10}
+ \change New macro set \cs{NewChemCompoundProperty}, see
+ section~\ref{sec:extend-comp-prop} for a description.
+\end{changes}
+
+\begin{changes}{4.11}
+ \change New macro set \cs{NewChemAdditionSymbol}, see
+ section~\ref{sec:addition-symbols}.
+ \change New macro set \cs{NewChemSymbol}, see section~\ref{sec:symbols}.
+\end{changes}
+
+\begin{changes}{4.12}
+ \change Change package requirement: \chemformula\ now not loads complete
+ \pkg{amsmath} but only \pkg{amstext}.
+\end{changes}
+
+\begin{changes}{4.13}
+ \change Check for blank input parts and don't process them.
+ \change Drop support for \cs*{[} and \cs*{]} as replacement for \code{[} and
+ \code{]} inside arrow captions.
+ \change New option \option{atom-format}.
+\end{changes}
+
+\begin{changes}{4.14}
+ \change New option \option{adduct-penalty}.
+\end{changes}
+
+\begin{changes}{4.15}
+ \change The order of arrow definitions doesn't matter any more.
+ \change New quasi equilibria arrows.
+ \change Require \pkg{amsmath}.
+ \change Allow \option{name-format} to end with a macro that takes an
+ argument.
+ \change Various bug fixes.
+\end{changes}
+
+\end{document}