chemformula

v4.15e 2017/03/23
typeset chemical compounds and reactions

Clemens Niederberger

http://www.mychemistry.eu/forums/forum/chemformula/

contact@mychemistry.eu

–
− 2e
0 0 I −I
+ –
2 Na + Cl2 2 Na + 2 Cl
–
+ 2e

Table of Contents
1. Introduction 2 7. Special Input Types 18
7.1. Single Token Groups . . . . . 18
2. Licence and Requirements 2 7.1.1. Addition Symbols . . . 18
7.1.2. Symbols . . . . . . . . 20
3. Setup 2 7.2. Option Input . . . . . . . . . . 20

4. The Basic Principle 3 8. Escaped Input 21

8.1. Text . . . . . . . . . . . . . . . 21
5. Stoichiometric Factors 4 8.2. Math . . . . . . . . . . . . . . 22

6. Compounds 7 9. Arrows 22
6.1. Adducts . . . . . . . . . . . . . 7 9.1. Arrow types . . . . . . . . . . 22
6.2. Subscripts . . . . . . . . . . . 7 9.2. Labels . . . . . . . . . . . . . . 24
6.3. Commands . . . . . . . . . . . 8 9.3. Customization . . . . . . . . . 25
6.4. Charges and Other Superscripts 9 9.4. Modify Arrow Types . . . . . 27
6.5. Bonds . . . . . . . . . . . . . . 11 9.5. Standalone Arrows . . . . . . 29
6.5.1. Native Bonds . . . . . 11
6.5.2. Flexible Bonds . . . . . 11 10. Names 29
6.6. Customization . . . . . . . . . 13 10.1. Syntax . . . . . . . . . . . . . 29
6.7. Standalone Formulae . . . . . 17 10.2. Customization . . . . . . . . . 30
6.8. Extend Compound Properties 17 10.3. Standalone Names . . . . . . . 30

1
 1. Introduction

11. Format and Font 31 15. Kröger-Vink Notation 36

12. Usage In Math Equations 33 A. History Since Version 4.0 37

13. Usage with TikZ or pgfplots and
externalization 34 B. References 39

14. Lewis Formulae 34 C. Index 39

1. Introduction
Probably every chemist using LATEX 2ε is aware of the great mhchem package by Martin Hensel.
There have always been some difficulties intertwining it with the chemmacros package,
though. Also, some other minor points in mhchem always bothered me, but they hardly
seemed enough for a new package. They weren’t even enough for a feature request to the
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 mhchem but is more strict as to how compounds,
stoichiometric factors and arrows are input. In the same time chemformula offers many
possibilities to customize the output.

2. Licence and Requirements

Permission is granted to copy, distribute and/or modify this software under the terms of the LATEX
Project Public License (LPPL), version 1.3 or later (http://www.latex-project.org/lppl.txt).
The software has the status “maintained.”
The chemformula package needs and thus loads the packages l3kernel [L3Pa], xparse,
l3keys2e and xfrac (all three are part of the l3packages bundle [L3Pb]), tikz1 [Tan13], ams-
text [MS00], nicefrac [Rei98] and scrlfile (from the KOMA - Script2 bundle [Koh15]).

3. Setup
If you’re using chemformula as a standalone package options are set up with the following
command:

\setchemformula{ hoptionsi }
Set up chemformula.

chemformula is tightly intertwined with the chemmacros package. If noth packages

are loaded together, chemformula is integrated into the chemmacros package. Then all of
chemformula’s options belong to chemmacros’ module chemformula. This means if you
load it via chemmacros or in addition to chemmacros they can be setup with
1. on CTAN as pgf: http://mirrors.ctan.org/graphics/pgf/
2. on CTAN as koma-script: http://mirrors.ctan.org/macros/latex/contrib/koma-script/

2
 4. The Basic Principle

\chemsetup[chemformula]{ hoptionsi }
Set up options for chemformula exclusively, or
\chemsetup{chemformula/ hoption1i ,chemformula/ hoption2i }
Set up options for chemformula together with others of chemmacros’ options.

4. The Basic Principle

chemformula offers one main command.
\ch[ hoptionsi ]{ hinputi }
chemformula’s main command.
The usage will seem very familiar to you if you’re familiar with mhchem:

H2O
1 \ch{H2O} \par Sb2O3
2 \ch{Sb2O3} \par H+
3 \ch{H+} \par CrO42–
\ch{CrO4^2-} \par
4
AgCl2–
5 \ch{AgCl2-} \par
6 \ch{[AgCl2]-} \par
[AgCl2]–
7 \ch{Y^{99}+} \par Y99+
8 \ch{Y^{99+}} \par Y99+
9 \ch{H2_{(aq)}} \par H2(aq)
10 \ch{NO3-} \par NO3–
11 \ch{(NH4)2S} \par (NH4)2S
12 \ch{^{227}_{90}Th+} \par 227 +
90Th
13 $V_{\ch{H2O}}$ \par
VH2O
14 \ch{Ce^{IV}} \par
15 \ch{KCr(SO4)2 * 12 H2O}
CeIV
KCr(SO4)2 · 12 H2O

However, there are differences. The most notable one: chemformula distinguishes between
different types of input. These different parts have to be separated with blanks:
\ch{part1 part2 part3 part4}

A blank in the input 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.
Another notable difference: chemformula tries to avoid math mode whenever possible:

a
1 \ch{A + B ->[a] C} \par A+B C
a
2 \ce{A + B ->[a] C} A + B −−−→ C

3
 5. Stoichiometric Factors

This means that \ch{2H2O} is recognized as a single part, which in this case is recognized as
a compound.

1 \ch{2H2O} \par 2H2O

2 \ch{2 H2O} 2 H2O

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 ~. However, since commands in
most cases gobble a space after them a input like \ch{\command ABC} will be treated as a single
part. If you want or need to divide them you need to add an empty group: \ch{\command{}
ABC}. The different input types are described in the following sections.

5. Stoichiometric Factors
A stoichiometric factor may only contain of numbers and the signs .,_/()

1 \ch{2} \par
2 \ch{12}
3
2
4 % decimals:
5 \ch{.5} \par
12
6 \ch{5,75} 0.5
7 5.75
3
8 % fractions: 2
9 \ch{3/2} \par 1 12
10 \ch{1_1/2} (1/2)
11

12 % ``iupac'':
13 \ch{(1/2)}

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.

1 this won't work but will result in an error: \ch{1/1_1}

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.

4
 5. Stoichiometric Factors

1 \ch{(1/2) H2O} \ch{1/2 H2O} \ch{0.5 H2O}

(1/2) H2O 12 H2O 0.5 H2O

You can find many examples like the following for stoichiometric factors in parentheses in the
IUPAC Green Book [Coh+08]:

(1/5) KMnVII O4 + (8/5) HCl = (1/5) MnII Cl2 + (1/2) Cl2 + (1/5) KCl + (4/5) H2O

There are a few possibilities to customize the output.

decimal-marker = { hmarkeri } Default: .
The symbol to indicate the decimal.

frac-style = math|xfrac|nicefrac Default: math

Determines how fractions are displayed.

frac-math-cmd = { hcommand sequencei } Default: \frac

Introduced in Allows you to choose which command is used with frac-style = {math}. This needs to be a
version 4.1 command sequence that takes two arguments that are set in math mode.

stoich-space = { hskipi } Default: .1667em plus .0333em minus .0117em

The space that is placed after the stoichiometric factor. A rubber length.

stoich-paren-parse = true|false Default: false

If set to true stoichiometric factors enclosed by parentheses also are parsed.

stoich-print = { hcsi } Default: \chstoich

This option allows to redefine the macro that prints the stoichiometric factors. hcsi should
be a macro that takes one mandatory argument. Please note that using this option will disable
chemformula’s stoichiometric parsing as that is done by the default command \chstoich.

1 \ch[decimal-marker={,}]{3.5} \ch[decimal-marker={$\cdot$}]{3,5}

3,5 3·5

The option frac-style = {xfrac} uses the \sfrac command of the xfrac package. The
output strongly depends on the font you use.

5
 5. Stoichiometric Factors

1 \ch[frac-style=xfrac]{3/2} \ch[frac-style=xfrac]{1_1/2}

3⁄2 11 ⁄ 2

chemformula defines the instance chemformula-text-frac which you can redefine to your
needs. See the xfrac documentation for further information. The default definition is this:

1 \DeclareInstance{xfrac}{chemformula-text-frac}{text}
2 {
3 slash-left-kern = -.15em ,
4 slash-right-kern = -.15em
5 }

This document uses the font Linux Libertine O and the following definition:

1 \DeclareInstance{xfrac}{chemformula-text-frac}{text}
2 {
3 scale-factor = 1 ,
4 denominator-bot-sep = -.2ex ,
5 denominator-format = \scriptsize #1 ,
6 numerator-top-sep = -.2ex ,
7 numerator-format = \scriptsize #1 ,
8 slash-right-kern = .05em ,
9 slash-left-kern = .05em
10 }

The option frac-style = {nicefrac} uses the \nicefrac command of the nicefrac package.

1 \ch[frac-style=nicefrac]{3/2} \ch[frac-style=nicefrac]{1_1/2}

3/2 11/2

The option stoich-space allows you to customize the space between stoichiometric factor
and the group following after it.

6
 6. Compounds

1 \ch{2 H2O} \par 2 H2O

2 \ch[stoich-space=.3em]{2 H2O} 2 H2O

6. 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.

1 \ch{H2SO4} \par H2SO4

2 \ch{[Cu(NH3)4]^2+} [Cu(NH3)4]2+

6.1. Adducts
chemformula has two identifiers which will create adducts.

\ch{A.B}
A·B

\ch{A*B}
A·B

1 \ch{CaSO4.H2O} \par CaSO4 · H2O

2 \ch{CaSO4*H2O} CaSO4 · H2O

Since numbers in a compound always are treated as subscripts (see section 6.2) you sometimes
need to introduce stoichiometric factors for the right output:

1 \ch{Na3PO4*12H2O} \par Na3PO4 · 12H2O

2 \ch{Na3PO4* 12 H2O} \par Na3PO4 · 12 H2O
3 \ch{Na3PO4 * 12 H2O} Na3PO4 · 12 H2O

6.2. Subscripts
All numbers in a compound are treated as subscripts.

7
 6. Compounds

1 \ch{H2SO4} H2SO4

If you want a letter to be a subscript you can use the math syntax:

1 \ch{A_nB_m} AnBm

The subscript recognizes groups. You can also use math inside it.

1 \ch{A_{$n$}B_{$m$}} \par An Bm
2 \ch{NaCl_{(aq)}} NaCl(aq)

6.3. Commands
Commands are allowed in a compound:

\ch{\textbf{A2}B3} \ch{A2\color{red}B
1
A2B3 A2B3
3}

However, if the commands demand numbers as argument, e. g., space commands or chem-
macros’ \ox command the direct use will fail. This is because the numbers are treated as
subscripts before the command expands.

1 \ch{A\hspace{2mm}B} will raise an error because \hspace sees something like

2 this: \hspace{$_2$mm}. Actually not at all like this but equally bad\ldots

See section 8.1 for a way around this.

Please also note that formulas are placed inside a group!

1 \ch{A2\color{red}B3 C4} A2B3C4

8
 6. Compounds

6.4. Charges and Other Superscripts

Basics If a compound 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 6.5.

1 \ch{A+B} \ch{AB+} \par A B AB+

2 \ch{A-B} \ch{AB-} A B AB–

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 + nor - are treated as
bonds. If a dot . is inside a superscript it is treated as indicator for a radical. A * gives the
excited state.

Ax–
1 \ch{A^{x-}} \par
2 \ch{A^x-} \par
Ax–
3 \ch{A^{x}-} \par Ax–
4 \ch{A^{$x-$}} \par Ax –
5 \ch{RNO2^{-.}} \par RNO2–
3
6 \ch{^31H} \par 1H
\ch{^{14}6C} \par 14
6C
7

8 \ch{^{58}_{26}Fe} \par 58
26Fe
9 \ch{NO^*}
NO*

Changed in Actually a dot . is not always treated as indicator for a radical: if the dot in the superscript is
version 4.5a followed by a number it is interpreted as a decimal sign. It is typeset according to the option
decimal-marker. This may be a good place to mention that a comma , in a superscript is also
typeset according to decimal-marker.

1 \ch{^{22,98}_{11}Na}
2 \ch{^{22.98}_{11}Na}\par 22.98 22.98
11Na 11Na
3 \setchemformula{decimal-marker={,}} 22,98 22,98
4 \ch{^{22,98}_{11}Na} 11Na 11Na
5 \ch{^{22.98}_{11}Na}

Ions and ion composites with more than one charge can be typeset quite as easy:

1 \ch{SO4^2-} \ch{Ca^2+ SO4^2-} SO42– Ca2+SO42–

9
 6. Compounds

Charge Commands You don’t need to use \mch and related commands inside \ch. Indeed,
you shouldn’t use them as they might mess with the subscript and superscript alignment. The
chemmacros option circled is obeyed by \ch.

1 \chemsetup[charges]{circled=all}
2 \ch{H+ + OH- <=> H2O}

H
+
+ OH
–
H2O

chemformula knows the options circled and circletype also on its own.

1 \setchemformula{circled=all}
2 \ch{H+ + OH- <=> H2O}

H
+
+ OH
–
H2O

These options are coupled with chemmacros options, i. e., setting chemmacros’ options
will also set chemformula’s equivalents. The other way around the options act independently:
setting chemformula’s options will not set chemmacros’ options.
circled = formal|all|none Default: formal
chemformula uses two different kinds of charges which indicate the usage of real (+/−) and
formal ( /
+ )
– charges. The choice formal distinguishes between them, choice none displays
them all without circle, choice all circles all.

circletype = chem|math Default: chem

This option switches between two kinds of circled charge symbols: \fplus
+ and $\oplus$ ⊕.

Behaviour The supercripts behave differently depending on their position in a compound, if

there are super- and subscripts following each other directly.

1 \ch{^33B} \ch{{}^33B} \ch{3^3B} \ch{B^3} \ch{B3^3} \par

2 \ch{^{23}_{123}B} \ch{{}^{23}_{123}B} \ch{_{123}^{23}B}
3 \ch{B^{23}} \ch{B_{123}^{23}} \par
4 \ch{^{123}_{23}B} \ch{{}^{123}_{23}B} \ch{_{23}^{123}B}
5 \ch{B^{123}} \ch{B23^{123}}

10
 6. Compounds

3 3 3 3 3
3B 3 B 3B B B3
23 23 23 23 23
123B 123B 123B B B123
123 123 123 123 123
23B 23 B 23B B B23

• If a compound starts with a sub- or superscript both sub- and superscript are aligned to
the right else to the left.

• If a compound 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
charge-hshift = { hdimi }, also see page 13f.

The second point follows IUPAC’s recommendations:

In writing the formula for a complex ion, spacing for charge number can be added (staggered
arrangement), as well as parentheses: SO42–, (SO4)2–. The staggered arrangement is now
recommended. IUPAC Green Book [Coh+08, p. 51]

6.5. Bonds
6.5.1. Native Bonds
There are three kinds of what I will call “native bonds”:

1 single: \ch{CH3-CH3} \par single: CH3 CH3

2 double: \ch{CH2=CH2} \par double: CH2 CH2
3 triple: \ch{CH+CH} triple: CH CH

6.5.2. Flexible Bonds

Predefined Bonds In addition to the three native bonds there are a few more which can be
called by

\bond{ hbond namei }

Prints the bond type specified by hbond namei.

The predefined bond types are shown in table 1 on the following page.

1 \ch{C\bond{sb}C\bond{db}C\bond{tp}C\bond{deloc}C\bond{tdeloc}C\bond{co>}C\bond
{<co}C}

11
 6. Compounds

Table 1: Bonds available with \bond.

name appearance aliases
single normal, sb
double db
triple tp
dotted semisingle
deloc semidouble
tdeloc semitriple
co> coordright
<co coordleft

C C C C C C C C

Own Bonds chemformula offers commands to define own bond types:

\NewChemBond{ hnamei }{ hcodei }
Introduced in Define the new bond type hnamei. Issue an error if a bond hnamei already exists.
version 4.3
\DeclareChemBond{ hnamei }{ hcodei }
Define the new bond type hnamei or overwrite it if it already exists.
\RenewChemBond{ hnamei }{ hcodei }
Redefine the existing bond type hnamei. Issue an error if a bond hnamei doesn’t exist.
\ProvideChemBond{ hnamei }{ hcodei }
Introduced in Define the new bond type hnamei only if it doesn’t exist yet.
version 4.12a
\NewChemBondAlias{ hnew namei }{ hold namei }
Introduced in Declare the bond type hnew namei to be an alias of hold namei. Issue an error if a bond hnew
version 4.3 namei already exists.
\DeclareChemBondAlias{ hnew namei }{ hold namei }
Declare the bond type hnew namei to be an alias of hold namei.
\ShowChemBond{ hnamei }
Print the definition of bond type hnamei.
The usage is best described with an example. So let’s see how the single bond and the co>
bond are defined:

1 \NewChemBond{single}
2 { \draw[chembond] (chemformula-bond-start) -- (chemformula-bond-end) ; }
3 \NewChemBond{coordright}

12
 6. Compounds

4 {
5 \draw[chembond,butt cap->]
6 (chemformula-bond-start) -- (chemformula-bond-end) ;
7 }
8 \NewChemBondAlias{co>}{coordright}

Two points are important: the names of the starting and the ending coordinates, chemformula-bond-start
and chemformula-bond-end, and the TikZ style of the bonds chembond.
So, let’s say you want to define a special kind of dashed bond. You could do this:

1 \usetikzlibrary{decorations.pathreplacing}
2 \makeatletter
3 \NewChemBond{dashed}
4 {
5 \draw[
6 chembond,
7 decorate,
8 decoration={
9 ticks,
10 segment length=\chemformula@bondlength/10,amplitude=1.5pt
11 }]
12 (chemformula-bond-start) -- (chemformula-bond-end) ;
13 }
14 \makeatother
15 \setchemformula{bond-length=2ex}
16 \ch{C\bond{dashed}C}

C C

The last example showed you another macro: \chemformula@bondlength. It only exists so
you can use it to access the bond length as set with bond-length directly.

6.6. Customization
These options allow you to customize the ouptut of the compounds:
subscript-vshift = { hdimi } Default: 0pt
Extra vertical shift of the subscripts.
subscript-style = text|math Default: text
Style that is used to typeset the subscripts.
charge-hshift = { hdimi } Default: .25em
Shift of superscripts when following a subscript.

13
 6. Compounds

charge-vshift = { hdimi } Default: 0pt

Extra vertical shift of the superscripts.

charge-style = text|math Default: text

Style that is used to typeset the superscripts.

circled = formal|all|none Default: formal

Introduced in Like chemmacros’ package option but local to chemformula’s \ch. That is: since chem-
version 4.6 macros’ macros use chemformula’s mechanism this is effectively an alias.

circletype = chem|math Default: chem

Introduced in Like chemmacros’ package option but local to chemformula’s \ch. That is: since chem-
version 4.6 macros’ macros use chemformula’s mechanism this is effectively an alias.

adduct-space = { hdimi } Default: .1333em

Space to the left and the right of the adduct point.

adduct-penalty = { hnumi } Default: 300

Introduced in The penalty inserted after the adduct point for (dis-)allowing line breaks.
version 4.14
bond-length = { hdimi } Default: .5833em
The length of the bonds.

bond-offset = { hdimi } Default: .07em

Space between bond and atoms.

bond-style = { hTikZi } (initially empty)

TikZ options for the bonds.

bond-penalty = { hnumi } Default: 10000

Introduced in The penalty that is inserted after a bond for (dis-)allowing line breaks.
version 4.0a
radical-style = { hTikZi } (initially empty)
TikZ options for the radical point.

radical-radius = { hdimi } Default: .2ex

The radius of the radical point.

radical-hshift = { hdimi } Default: .15em

Horizontal shift before the radical point is drawn.

radical-vshift = { hdimi } Default: .5ex

Vertical shift relative to the current baseline.

radical-space = { hdimi } Default: .15em

Horizontal shift after the radical point is drawn.

Maybe you have noticed that charges of certain ions are shifted to the right.

14
 6. Compounds

1 \ch{SO4^2-} \ch{NH4+} \ch{Na+} SO42– NH4+ Na+

They are shifted if they follow a subscript which follows IUPAC recommendations [Coh+08,
p. 51]. The amount of the shift can be set with the option charge-hshift.

1 \ch{SO4^2-} \ch{NH4+} \ch{Na+} \par

2 \setchemformula{charge-hshift=.5ex}
3 \ch{SO4^2-} \ch{NH4+} \ch{Na+} \par
4 \setchemformula{charge-hshift=.5pt}
5 \ch{SO4^2-} \ch{NH4+} \ch{Na+}

SO42– NH4+ Na+

SO42– NH4+ Na+
SO42– NH4+ Na+

Despite IUPAC’s recommendation chemformula does not make fully staggered arrange-
ments 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
charge-hshift = {full}.

1 \ch[charge-hshift=0pt]{C5H11+} \ch[charge-hshift=0pt]{SO4^2-} \par

2 \ch{C5H11+} \ch{SO4^2-} \par
3 \ch[charge-hshift=1ex]{C5H11+} \ch[charge-hshift=1ex]{SO4^2-} \par
4 \ch[charge-hshift=full]{C5H11+} \ch[charge-hshift=full]{SO4^2-}

C5H+11 SO2–
4
C5H11+ SO42–
C5H11+ SO4 2–
C5H11+ SO42–

If you don’t want the charges to be typeset in text mode you can switch to math mode:

15
 6. Compounds

1 \ch{M^x+} \ch{SO4^2-} \par

2 \setchemformula{charge-style = math}
3 \ch{M^x+} \ch{SO4^2-}

Mx+ SO42–
Mx + SO42−

The option subscript-vshift can be used to adjust the vertical shift of the subscripts:

1 \ch{H2SO4} \ch{Na3PO4} \par

2 \setchemformula{subscript-vshift=.5ex}
3 \ch{H2SO4} \ch{Na3PO4} \par
4 \setchemformula{subscript-vshift=-.2ex}
5 \ch{H2SO4} \ch{Na3PO4}

H2SO4 Na3PO4
H2SO4 Na3PO4
H2SO4 Na3PO4

You can choose the mode subscripts are typeset in the same way as it is possible for the
charges:

1 \ch{A_nB_m} \ch{H2SO4} \par

2 \setchemformula{subscript-style = math}
3 \ch{A_nB_m} \ch{H2SO4}

AnBm H2SO4
An Bm H2SO4

The option adduct-space sets the space left and right to the adduct symbol ·.

1 \ch{Na3PO3*H2O} \par
2 \setchemformula{adduct-space=.2em}

16
 6. Compounds

3 \ch{Na3PO3*H2O}

Na3PO3 · H2O
Na3PO3 · H2O

Changing the length of the bonds:

1 \setchemformula{bond-length=4mm}%
2 single: \ch{CH3-CH3} \par
3 double: \ch{CH2=CH2} \par
4 triple: \ch{CH+CH}

single: CH3 CH3

double: CH2 CH2
triple: CH CH

You can change the distance between bond and atom, too:

1 \ch{H-H + N+N + O=O} \par

2 \ch[bond-offset=1pt]{H-H + N+N + O=O}

H H+N N+O O
H H+N N+O O

6.7. Standalone Formulae

Introduced in chemformula offers a command that only accepts the “compound” input type:
version 4.0
\chcpd[ hoptionsi ]{ hcompoundi }
Typeset single compounds.

6.8. Extend Compound Properties

Introduced in It is possible to extend the range of special input symbols within compounds. In the default
version 4.10 setting those are *.-=+' and arabic numerals. Others can be added or the existing ones be
changed with one of the following commmands:

17
 7. Special Input Types

\NewChemCompoundProperty{ htokeni }{ hreplacementi }

htokeni will be replaced by hreplacementi within compounds. The property is only added if
htokeni is not yet part the compounds’ property list. Otherwise an error is issued.

\ProvideChemCompoundProperty{ htokeni }{ hreplacementi }

Introduced in htokeni will be replaced by hreplacementi within compounds. The property is only added if
version 4.12a htokeni is not yet part the compounds’ property list.

\RenewChemCompoundProperty{ htokeni }{ hreplacementi }

htokeni will be replaced by hreplacementi within compounds. The property is only added if
htokeni is already part the compounds’ property list. Otherwise an error is issued.

\DeclareChemCompoundProperty{ htokeni }{ hreplacementi }

htokeni will be replaced by hreplacementi within compounds. The property silently overwrites
any previously set hreplacementi for htokeni if htokeni is already part the compounds’ property
list.

\RemoveChemCompoundProperty{ htokeni }
Removes htokeni from the compounds’ property list.
For example you can use

1 \NewChemCompoundProperty{\}{\slash}

to allow line breaks after slashes in compounds.

7. Special Input Types

There are some “special type” input groups.

7.1. Single Token Groups

The first kind are groups which consist of only one token. They are again divided into two
groups, “addition symbols” and “symbols”.

7.1.1. Addition Symbols

\ch{ + } +
Creates the plus sign between compounds with space around it:
\ch{2 Na + Cl2} 2 Na + Cl2

\ch{ - } −
Introduced in Creates the minus sign between compounds with space around it:
version 4.3a \ch{M - H} M − H

18
 7. Special Input Types

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:

\NewChemAdditionSymbol{ hnamei }{ hinputi }{ houtputi }

Introduced in Defines the addition symbol hnamei with input symbol hinputi and output houtputi.
version 4.11
\ProvideChemAdditionSymbol{ hnamei }{ hinputi }{ houtputi }
Introduced in Defines the addition symbol hnamei with input symbol hinputi and output houtputi only no
version 4.12a addition symbol with then name hnamei doesn’t exist.

\RenewChemAdditionSymbol{ hnamei }{ hinputi }{ houtputi }

Introduced in Redefines the addition symbol hnamei with input symbol hinputi and output houtputi.
version 4.11
\DeclareChemAdditionSymbol{ hnamei }{ hinputi }{ houtputi }
Introduced in (Re-)Defines the addition symbol hnamei with input symbol hinputi and output houtputi without
version 4.11 checking if the symbol exists or not.

The space left and right of the plus and the minus sign and the signs themselves can be set
with the following options:

plus-space = { hskipi } Default: .3em plus .1em minus .1em

A rubber length.

plus-penalty = { hnumi } Default: 700

Introduced in The penalty that is inserted after the plus sign for (dis-)allowing line breaks.
version 4.0a
plus-output-symbol = { hcodei } Default: +
Introduced in The hcodei that is used for the plus sign.
version 4.9
minus-space = { hskipi } Default: .3em plus .1em minus .1em
Introduced in A rubber length.
version 4.9
minus-penalty = { hnumi } Default: 700
Introduced in The penalty that is inserted after the minus sign for (dis-)allowing line breaks.
version 4.9
minus-output-symbol = { hcodei } Default: $-$
Introduced in The hcodei that is used for the minus sign.
version 4.9
The corresponding three options are defined when \NewChemAdditionSymbol or one of the
variants is used, hnamei -space and hnamei -penalty both with the same defaults as above, and
hnamei -output-symbol.

1 \ch{A + B}\par A+B

2 \ch[plus-space=4pt]{A + B} A+B

19
 7. Special Input Types

7.1.2. Symbols
\ch{ v } ↓
Sign for precipitate: \ch{BaSO4 v} BaSO4↓

\ch{ ^ } ↑
Sign for escaping gas3: \ch{H2 ^} H2↑

You can define/redefine your own symbols:

\NewChemSymbol{ hinputi }{ houtputi }

Introduced in Defines the addition symbol with input hinputi and output houtputi.
version 4.11
\ProvideChemSymbol{ hinputi }{ houtputi }
Introduced in Defines the addition symbol with input hinputi and output houtputi only if no symbol with
version 4.12a input hinputi exists.

\RenewChemSymbol{ hinputi }{ houtputi }

Introduced in Redefines the addition symbol with input hinputi and output houtputi.
version 4.11
\DeclareChemSymbol{ hinputi }{ houtputi }
Introduced in (Re-)Defines the addition symbol with input hinputi and output houtputi without checking if
version 4.11 the symbol exists or not.

7.2. 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 \ch several times.

1 \ch{H2O +}\textcolor{red}{\ch{H2SO4}}\ch{-> H3O+ + HSO4-} \par

2 \ch{H2O +}\ch[subscript-vshift=2pt]{H2SO4}\ch{-> H3O+ + HSO4-}

H2O + H2SO4 H3O+ + HSO4–

H2O + H2SO4 H3O+ + HSO4–

This, however, interrupts the input in your source and may mess with the spacing. That’s why
there is an alternative:

\ch{ @{ hoptionsi } }
The options specified this way will be valid only until the next compound is set.

3. Is this the correct English term? Please correct me if it isn’t.

20
 8. Escaped Input

1 \ch{H2O +}\textcolor{red}{\ch{H2SO4}}\ch{-> H3O+ + HSO4-} \par

2 \ch{H2O + @{format=\color{red}} H2SO4 -> H3O+ + HSO4-} \par
3 or of course:\par
4 \ch{H2O + \textcolor{red}{H2SO4} -> H3O+ + HSO4-}\par\bigskip
5 \ch{H2O +}\ch[subscript-vshift=2pt]{H2SO4}\ch{-> H3O+ + HSO4-} \par
6 \ch{H2O + @{subscript-vshift=2pt} H2SO4 -> H3O+ + HSO4-}

H2O + H2SO4 H3O+ + HSO4–

H2O + H2SO4 H3O+ + HSO4–
or of course:
H2O + H2SO4 H3O+ + HSO4–

H2O + H2SO4 H3O+ + HSO4–

H2O + H2SO4 H3O+ + HSO4–

8. Escaped Input
In some cases it may be desirable to prevent chemformula from parsing the input. This can
be done in two ways.

8.1. Text
If you put something between " " or ' ' then the input will be treated as normal text, except
that spaces are not allowed and have to be input with ~.

\ch{ " hescapedtexti " }

One of two possibilities to escape chemformula’s parsing.

\ch{ ' hescapedtexti ' }

The second of two possibilities to escape chemformula’s parsing.

1 \ch{"\ox{2,Ca}" O} \par
2 \ch{"\ldots\," Na + "\ldots\," Cl2 -> "\ldots\," NaCl} \par
3 \ch{'A~->~B'}

CaII O
. . . Na + . . . Cl2 . . . NaCl
A -> B

21
 9. Arrows

In many cases you won’t need to escape the input. But when you get into trouble when using a
command inside \ch try hiding it.

8.2. Math
If you especially want to input math you just enclose it with $ $. 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.
\ch{ $ hescapedmathi $ }
One of two possibilities to escape chemformula’s parsing into math mode.
\ch{ \( hescapedmathi \) }
The second of two possibilities to escape chemformula’s parsing into math mode.

1 escaped text: \ch{"$x$" H2O} \par escaped text: xH2O

2 escaped math: \ch{$x$ H2O} \par escaped math: x H2O
3 also escaped math: \ch{\(x\) H2O} \par also escaped math: x H2O
4 \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl} 2n Na + n Cl2 2n NaCl

The space that is inserted after a math group can be edited:

math-space = { hskipi } Default: .1667em plus .0333em minus .0117em
A rubber length.

1 \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl} \par

2 \setchemformula{math-space=.25em}
3 \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl} \par
4 \ch{$A->B$}

2n Na + n Cl2 2n NaCl
2n Na + n Cl2 2n NaCl
A− > B

9. Arrows
9.1. Arrow types
Arrows are input in the same intuitive way they are with mhchem. There are various different
types:

22
 9. Arrows

->
standard right arrow

<-
standard left arrow

-/>
does not react (right)

</-
does not react (left)

<->
resonance arrow

<>
reaction in both directions

== =
stoichiometric equation

<=>
equilibrium arrow

>=<
Introduced in reversed equilibrium arrow
version 4.5
<=>>
unbalanced equilibrium arrow to the right

>=<<
Introduced in reversed unbalanced equilibrium arrow to the right
version 4.5
<<=>
unbalanced equilibrium arrow to the left

>>=<
Introduced in reversed unbalanced equilibrium arrow to the left
version 4.5
<=o>
Introduced in quasi equilibrium arrow
version 4.15
<=o>>
Introduced in unbalanced quasi equilibrium arrow to the right
version 4.15
<<=o>
Introduced in unbalanced quasi equilibrium arrow to the left
version 4.15
<o>
isolobal arrow

23
 9. Arrows

<==>
Introduced in I’ve seen this one used. I’m not sure it actually has a meaning in chemical equations. If you
version 4.5 have some official reference for this arrow type please feel free to contact me.
All these arrows are drawn with TikZ.

1 \ch{H2 + Cl2 -> 2 HCl} \par

2 \ch{H2O + CO3^2- <=> OH- + HCO3-} \par
3 \ch{A <- B} \par
4 \ch{\{[CH2=CH-CH2]- <-> {}[CH2-CH=CH2]- \}} \par
5 \ch{A <> B} \par
6 \ch{H+ + OH- <=>> H2O} \par
7 \ch{2 NO2 <<=> N2O4}

H2 + Cl2 2 HCl
2–
H2O + CO3 OH– + HCO3–
A B
{[CH2 CH CH2]– [CH2 CH CH2]–}
A B
H+ + OH– H2O
2 NO2 N2O4

9.2. Labels
The arrows take two optional arguments to label them.
->[ habovei ][ hbelowi ]
Add text above or under an arrow.

a
1 \ch{A ->[a] B} \par A B
a
2 \ch{A ->[a][b] B} \par A b ◦
B
3 \ch{A ->[\SI{100}{\celsius}] B} 100 C
A B

The label text can be parsed seperately from the arrow. The recipe is easy: leave blanks.

H2O
1 \ch{A ->[H2O] B} \par
A B
H2O
2 \ch{A ->[ H2O ] B} \par A B
3 \ch{A ->[ "\ox{2,Ca}" F2 ] B} \par
CaII F2
A B
4 \ch{A ->[ $\Delta$,~ [ H+ ]] B} ∆, [H+]
A B

24
 9. Arrows

If you leave the blanks chemformula treats the groups inside the square brackets as
seperated input types. The arrow reads its arguments afterwards. As you can see the arrows
“grow” with the length of the labels. What stays constant is the part that protrudes the labels.

1 \ch{A ->[a] B} \par

2 \ch{A ->[ab] B} \par
3 \ch{A ->[abc] B} \par
4 \ch{A ->[abc~abc] B} \par
5 % needs the `chemfig' package:
6 \setatomsep{15pt}
7 \ch{A ->[ "\chemfig{-[:30]-[:-30]OH}" ] B} \par

a
A B
ab
A B
abc
A B
abc abc
A B
OH
A B

9.3. Customization
These are the options which enable you to customize the arrows:

arrow-offset = { hdimi } 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 arrow-offset.

arrow-min-length = { hdimi } Default: 0pt

Introduced in The minimal length an error must have unless two times arrow-offset plus the width of the
version 3.6b label is larger.

arrow-yshift = { hdimi } Default: 0pt

Shifts an arrow up (positive value) or down (negative value).

arrow-ratio = { h<factor>i } Default: .6

The ratio of the arrow lengths of the unbalanced equilibrium. .4 would mean that the length of
the shorter arrow is 0.4× the length of the longer arrow.

compound-sep = { hdimi } Default: .5em

The space between compounds and the arrows.

label-offset = { hdimi } Default: 2pt

The space between the labels and the arrows.

25
 9. Arrows

label-style = { hfont commandi } Default: \footnotesize

The relative font size of the labels.

arrow-penalty = { hnumi } Default: 0

Introduced in The penalty that is inserted after an arrow for (dis-)allowing line breaks.
version 4.0a
arrow-style = { hTikZi } (initially empty)
Introduced in Additonal TikZ keys for formatting the arrows.
version 4.1a
The following code shows the effect of the different options on the <=>> arrow:

1 standard: \ch{A <=>>[x][y] B} \par

2 longer: \ch[arrow-offset=12pt]{A <=>>[x][y] B} \par
3 higher: \ch[arrow-yshift=2pt]{A <=>>[x][y] B} \par
4 more balanced: \ch[arrow-ratio=.8]{A <=>>[x][y] B} \par
5 labels further away: \ch[label-offset=4pt]{A <=>>[x][y] B} \par
6 larger distance to compounds: \ch[compound-sep=2ex]{A <=>>[x][y] B} \par
7 smaller labels: \ch[label-style=\tiny]{A <=>[x][y] B}

x
standard: A y B
x
longer: A y B
x
higher: A y B
x
more balanced: A y B
x
labels further away: A y B
x
larger distance to compounds: A y B
x
smaller labels: A y B

Introduced in If you want to have different arrow tips there is an easy way to use existing arrow tips (as
version 4.7 defined by TikZ). chemformula uses three different arrow tips: cf, left cf and right cf.
If you want them to match those of chemfig [Tel15] for example you could do:

1 \pgfkeys{
2 cf /.tip = {CF@full} ,
3 left cf /.tip = {CF@half}
4 }

chemfig has no equivalent of right cf. This mechanism relies on TikZ version 3.0.0 and the
new arrows.meta library.

26
 9. Arrows

9.4. Modify Arrow Types

The arrows are defined with the commands

\NewChemArrow{ htypei }{ hTikZi }

Define the new arrow type htypei. Issue an error if an arrow type htypei already exists.

\ProvideChemArrow{ htypei }{ hTikZi }

Introduced in Define the new arrow type htypei only if it doesn’t exist, yet.
version 4.12a
\DeclareChemArrow{ htypei }{ hTikZi }
Define the new arrow type htypei or overwrite it if it already exists.

\RenewChemArrow{ htypei }{ hTikZi }

Redefine the arrow type htypei. Issue an error if an arrow type htypei doesn’t exist.

\ShowChemArrow{ htypei }
Print out the current definition of the arrow type htypei.

htypei is the sequence of tokens that is replaced with the actual arrow code. For example the
basic arrow is defined via

1 \NewChemArrow{->}{
2 \draw[chemarrow,-cf] (cf_arrow_start) -- (cf_arrow_end) ;
3 }

In order to define arrows yourself you need to know the basics of TikZ.4 The predefined arrows
use the arrow tips cf, left cf and right cf. They also all except the net reaction arrow ==
use the TikZ-style chemarrow that you should use, too, if you want the 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:

(cf_arrow_start)
The beginning of the arrow.

(cf_arrow_end)
The end of the arrow.

(cf_arrow_mid)
The mid of the arrow.

(cf_arrow_mid_start)
The beginning of the shorter arrow in types like <=>>.
4. Please see the pgfmanual for details.

27
 9. Arrows

(cf_arrow_mid_end)
The end of the shorter arrow in types like <=>>.

cf
A double-sided arrow tip.

left cf
A left-sided arrow tip.

right cf
A right-sided arrow tip.

chemarrow
chemformula’s TikZ-style that is applied to the arrows and set with arrow-style

1 \NewChemArrow{.>}{
2 \draw[chemarrow,-cf,dotted,red] (cf_arrow_start) -- (cf_arrow_end);
3 }
4 \NewChemArrow{n>}{
5 \draw[chemarrow,-cf]
6 (cf_arrow_start)
7 .. controls ([yshift=3ex]cf_arrow_mid) ..
8 (cf_arrow_end);
9 }
10 \ch{A .> B} \ch{A .>[a][b] B} \ch{A n> B}

a
A BA b
BA B

1 \texttt{\ShowChemArrow{->}} \par
2 \RenewChemArrow{->}{\draw[chemarrow,->,red] (cf_arrow_start) -- (cf_arrow_end)
;}
3 \texttt{\ShowChemArrow{->}} \par
4 \ch{A -> B}

\draw [chemarrow,-cf](cf_arrow_start)--(cf_arrow_end);
\draw [chemarrow,->,red] (cf_arrow_start) -- (cf_arrow_end) ;
A B

28
 10. Names

9.5. Standalone Arrows

Introduced in chemformula offers a command that only accepts the “arrow” input type:
version 4.0
\charrow{ htypei }[ habovei ][ hbelowi ]
Print the arrow type htypei.

This command is internally used for the arrows, too, when \ch is parsed.

10. Names
10.1. Syntax
chemformula has a built-in syntax to write text under a compound. In a way it works very
similar to the arrows.

\ch{ !( htexti )( hformulai ) }

Writes htexti below hformulai.

If an exclamation mark is followed by a pair of parentheses chemformula will parse it this

way:

1 \ch{!(ethanol)( CH3CH2OH )}

CH3CH2OH
ethanol

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.

1 \ch{!(water)(H2O)} \quad
2 \ch{!( "\textcolor{blue}{water}" )( H2O )} \quad
3 \ch{!( $2n-1$ )( H2O )} \quad
4 \ch{!( H2O )( H2O )} \quad
5 \ch{!(oxonium)( H3O+ )}

H2O H2O H2O H2O H3O+

water water 2n − 1 H2O oxonium

29
 10. Names

If for some reason you want to insert an exclamation mark without it creating a name you only
have to make sure it isn’t followed by parentheses.

1 \ch{H2O~(!)} \par H2O (!)

2 \ch{A!{}()} A!()

10.2. Customization
chemformula provides two options to customize the output of the names:

name-format = { hcommandsi } Default: \scriptsize\centering

The format of the name. This can be arbitrary input.

name-width = hdimi |auto Default: auto

The width of the box where the label is put into. auto will detect the width of the name and set
the box to this width.

1 \ch{!(acid)( H2SO4 ) -> B} \par

2 \ch[name-format=\sffamily\small]{!(acid)( H2SO4 ) -> B} \par
3 \ch[name-format=\scriptsize N:~]{!(acid)( H2SO4 ) -> B} \par
4 \ch[name-width=3em,name-format=\scriptsize\raggedright]{!(acid)( H2SO4 ) -> B}

H2SO4 B
acid
H2SO4 B
acid
H2SO4 B
N: acid
H2SO4 B
acid

10.3. Standalone Names

Introduced in chemformula offers a command that allows the usage of the “name” syntax in normal text.
version 4.0 This is the command that a bang is replaced with in chemformula’s formulas, actually. Both
arguments are mandatory.

1i )( htext 2i )
\chname( htext
The command that is useed internally for placing htext 1i below of htext 2i.

30
 11. Format and Font

11. Format and Font

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:

1 \newcommand*\sample{%
2 \ch{H2C-C+C-CH=CH+ + CrO4^2-
3 <=>[x][y]
4 2.5 Cl^{-.} + 3_1/2 Na*OH_{(aq)} + !(name)( A^n ) "\LaTeXe"}
5 }
6 \sample

x
H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 21 Na · OH(aq) + An LATEX 2ε
name

Now we’re going to change different aspects of the font a look what happens:

1 \sffamily Hallo \sample \\

2 \ttfamily Hallo \sample \normalfont \\
3 \bfseries Hallo \sample \normalfont \\
4 \itshape Hallo \sample

x
Hallo H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 21 Na · OH(aq) + An LATEX 2ε
name
x
Hallo H2C C C CH CH+ + CrO42- y 2.5 Cl- + 3 21 Na · OH(aq) + An LATEX 2ε
name
x
Hallo H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 12 Na · OH(aq) + An LATEX 2ε
name
+ x
Hallo H2C C C CH CH + CrO42– y
–
2.5 Cl + 3 21 Na · OH(aq) + n A
A L T X 2ε
E
name

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:

format = { hcodei } (initially empty)

Adds hcodei before the output of \ch.

atom-format = { hcodei } (initially empty)

Introduced in This adds hcodei before each formula. This allows to specify a format for the chemical formulas
version 4.13 only and have a different format for the rest of the chemical equation.

31
 11. Format and Font

1 \definecolor{newblue}{rgb}{.1,.1,.5}
2 \setchemformula{format=\color{newblue}\sffamily}
3 \sffamily Hallo \sample \\
4 \ttfamily Hallo \sample \normalfont \\
5 \bfseries Hallo \sample \normalfont \\
6 \itshape Hallo \sample

x
Hallo H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 21 Na · OH(aq) + An LATEX 2ε
name
x
Hallo H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 21 Na · OH(aq) + An LATEX 2ε
name
+ x
Hallo H2C C C CH CH + CrO42– y
–
2.5 Cl + 3 21 Na · OH(aq) + An LATEX 2ε
name
+ x
Hallo H2C C C CH CH + CrO42– y
–
2.5 Cl + 3 12 Na · OH(aq) + n A
A L T X 2ε
E
name

You can also specifically change the fontfamily, fontseries and fontshape of the output.

font-family = { hfamilyi } (initially empty)

Changes the fontfamily of the output with \fontfamily{ hfamilyi }.

font-series = { hseriesi } (initially empty)

Changes the fontseries of the output with \fontseries{ hseriesi }.

font-shape = { hshapei } (initially empty)

Changes the fontshape of the output with \fontshape{ hshapei }.

1 \setchemformula{font-series=bx}
2 Hallo \sample \par
3 \sffamily Hallo \sample \normalfont \par
4 \setchemformula{font-family=lmss,font-series=m} Hallo \sample
5 \normalfont \par
6 \itshape Hallo \sample

x
Hallo H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 12 Na · OH(aq) + An LATEX 2ε
name
x
Hallo H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 12 Na · OH(aq) + An LATEX 2ε
name
x
Hallo H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 12 Na · OH(aq) + An LATEX 2ε
name

32
 12. Usage In Math Equations

x
Hallo H2C C C CH CH+ + CrO42– y 2.5 Cl– + 3 12 Na · OH(aq) + An LATEX 2ε
name

If you’re using XELATEX or LuaLATEX and have loaded fontspec you have the possibilty to set
the font with it:

font-spec = { hfonti } (initially empty)

Use font hfonti for chemformula’s formulas.

or with options

font-spec = {[ hoptionsi ] hfonti }

Use font hfonti with options hoptionsi for chemformula’s formulas.

Since this document is typeset with pdfLATEX the option cannot be demonstrated here.

12. Usage In Math Equations

The \ch command can be used inside math equations. It recognizes \\ and & and passes them
on. However, you can’t use the optional arguments of \\ inside \ch.

1 \begin{align}
2 \ch{
3 H2O & ->[a] H2SO4 \\
4 Cl2 & ->[x][y] CH4
5 }
6 \end{align}
7 \begin{align*}
8 \ch{
9 RNO2 &<=>[ + e- ] RNO2^{-.} \\
10 RNO2^{-.} &<=>[ + e- ] RNO2^2-
11 }
12 \end{align*}

a
H2O H2SO4 (1)
x
Cl2 y CH4 (2)

+ e–
RNO2 RNO2–
+ e–
RNO2– RNO22–

33
 13. Usage with TikZ or pgfplots and externalization

13. Usage with TikZ or pgfplots and externalization

Introduced in Since chemformula uses TikZ to draw reaction arrows and bonds they would be externalized,
version 4.1 too, if you use that facility with TikZ or pgfplots5 [Feu13]. 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:

tikz-external-disable = true|false Default: true

dis- or enable TikZ’ externalization mechanism for chemformula’s arrows and bonds.

If you should be using a formula that contains bonds or arrows inside of a tikzpicture that
is externalized you should locally enable it for chemformula, too:

1 \begin{tikzpicture}
2 \setchemformula{tikz-external-disable=false}
3 \begin{axis}[xlabel={\ch{2 H+ + 2 e- -> H2}}]
4 \addplot ... ;
5 \end{axis}
6 \end{tikzpicture}

14. Lewis Formulae

Introduced in chemformula offers a command to typeset Lewis formulae. This does not mean Lewis
version 4.2 structures! Those can be achieved using the chemfig package [Tel15]. chemformula provides
the possibility to draw electrons as dots and pairs of dots or a line around an atom.

speci }{ hatomi }
\chlewis[ hoptionsi ]{ helectron
Draws electrons around the hatomi according to helectron speci.

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 hangleihseparatori. hanglei is a positiv or negativ
integer denoting the angle counter clockwise to the horizontal where the electrons should be
drawn. hseparatori is either a dot (., single electron), a colon (:, electron pair), a vertical line (|,
electron pair), an o (o, empty pair), or a comma (, default spec).

\chlewis{ hangle1ihtype1ihangle2ihtype2i }{ hatomi }

For example: \chlewis{0,180}{O} gives O and \chlewis{0.90.180.270.}{C} gives C .

The appearance can be influenced by a number of options:

5. on CTAN as pgfplots: http://mirrors.ctan.org/macros/latex/contrib/pgfplots/

34
 14. Lewis Formulae

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 helectron speci.

lewis-distance = { hdimi } Default: 1ex

The distance of two electrons in a pair.

lewis-line-length = { hdimi } Default: 1.5ex

The length of the line representing an electron pair.

lewis-line-width = { hdimi } Default: 1pt

The thickness of a line representing an electron pair.

lewis-offset = { hdimi } Default: .5ex

The distance of the symbols from the atom.
The dots are drawn according to the radical-radius option mentioned in section 6.6.
The basic usage should be more or less self-explaining:

1 \chlewis{0:90|180.270}{O}
2 \quad
3 \chlewis{45,135}{O} O O Na
4 \quad
5 \chlewis{0o}{Na}

The next example shows the effect of some of the options:

1 \chlewis[lewis-default=.]{23,68,113,158,203,248,293,338}{X}
2 \quad
3 \chlewis{0,90,180,270}{X}
4 \quad
5 \chlewis[lewis-distance=1.25ex]{0,90,180,270}{X}
6 \quad
7 \chlewis[lewis-distance=.75ex,radical-radius=.5pt]{0,90,180,270}{X}
8 \quad
9 \chlewis[
10 radical-radius=.5pt,
11 lewis-default=.
12 ]{23,68,113,158,203,248,293,338}{X}

X X X X X

35
 15. Kröger-Vink Notation

1 \ch{
2 !($1s^22s^1$)( "\chlewis{180.}{Li}" ) +
3 !($1s^22s^22p^5$)( "\chlewis{0.90,180,270}{F}" )
4 ->
5 !($1s^2$)( Li+ ) + !($1s^22s^22p^6$)( "\chlewis{0,90,180,270}{F}" {}- )
6 }

Li + F Li+ + F –

1s 2 2s 1 1s 2 2s 2 2p 5 1s 2 1s 2 2s 2 2p 6

15. Kröger-Vink Notation

Introduced in chemformula also supports the Kröger-Vink notation.
version 4.5
kroeger-vink = true|false Default: false
Enable the Kröger-Vink notation. As most options this can be enabled globally via the setup
command or locally as option to \ch.

With this option enabled several changes come into effect: ' produces a prime, a x in a
superscript produces ×, and both a . and a * 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.

1 \setchemformula{kroeger-vink=true}
2 \ch{Al_{Al}^'}
0 0
3 \ch{Al_{Al}'}\par AlAl AlAl
4 \ch{Ni_{Cu}^{x}}\par Ni×Cu
5 \ch{V_{Cl}^.} VCl VCl
6 \ch{V_{Cl}^*}\par
Cai
7 \ch{Ca_i^{..}}\par
e0
8 \ch{e^'}\par
9 \ch{Cl_i^'}
Cli0 Cli0
10 \ch{Cl_i'}\par Oi00 Oi00
11 \ch{O_i^{''}}
12 \ch{O_i''}

There are a number of options for customizations:

kv-positive-style = { hTikZi } (initially empty)

TikZ code for positive charge dot.

36
 A. History Since Version 4.0

kv-positive-radius = { hdimi } Default: .3ex

Radius of positive charge dot
kv-positive-hshift = { hdimi } Default: .15em
Horizontal shift of positive charge dot
kv-positive-vshift = { hdimi } Default: .5ex
Vertical shift positive charge dot
kv-positive-offset = { hdimi } Default: .4em
The offset of two consecutive positive charge dots
kv-neutral-symbol = { hTEX codei } Default: $\times$
Symbol for neutral particles.

A. History Since Version 4.0

Version 4.0
Introduced in • Since version 4.0, the chemformula package is distributed independently from chem-
version 4.0 macros.

Version 4.1
• New option tikz-external-disable.
• New option frac-math-cmd.

Version 4.2
• New option arrow-style.
• New command \chlewis that allows to add Lewis electrons to an atom, see section 14.

Version 4.3
• New option stoich-print.
• New command \chstoich.
• The commands \DeclareChem h...i now don’t give an error any more if the command
already exists. This is more consistent with LATEX’s \DeclareRobustCommand. For all
those commands a version \NewChem h...i is introduced that does give an error if the new
command is already defined.

Version 4.4
• A single dash - in \ch is now treated as a minus sign. This is consistent with the behaviour
of a +.

37
 A. History Since Version 4.0

Version 4.5
• New arrow types >=<, >=<<, >>=< and <==>.

• Internal changes to \ch allow usage of optional arguments of \\ and \label in chem-
macros’ reactions environment.

Version 4.6
• New options circled and circletype. this allows to set the behaviour as described on
chemmacros’ manual for a specific usage of \ch.

Version 4.7
• Dependency change: chemformula now requires the TikZ library arrows.meta instead
of the library arrows. This requires TikZ version 3.0.0.

Version 4.8
• The chemformula package now is no longer part of the chemmacros bundle but is
distributed as a package of it’s own.

Version 4.9
• New options minus-space and minus-penalty equivalent to the existing plus-space
and plus-penalty

• New options plus-output-symbol and minus-output-symbol for customizing the plus

and minus signs in the output.

Version 4.10
• New macro set \NewChemCompoundProperty, see section 6.8 for a description.

Version 4.11
• New macro set \NewChemAdditionSymbol, see section 7.1.1.

• New macro set \NewChemSymbol, see section 7.1.2.

Version 4.12
• Change package requirement: chemformula now not loads complete amsmath but
only amstext.

38
Version 4.13
• Check for blank input parts and don’t process them.

• Drop support for \[ and \] as replacement for [ and ] inside arrow captions.

• New option atom-format.

Version 4.14
• New option adduct-penalty.

B. References
[Coh+08] E. Richard Cohan et al.
“Quantities, Symbols and Units in Physical Chemistry”, IUPAC Green Book.
3rd Edition. 2nd Printing. IUPAC & RSC Publishing, Cambridge, 2008.
[Feu13] Christian Feuersänger. pgfplots. version 1.9, Oct. 4, 2013 (or newer).
url: http://mirror.ctan.org/graphics/pgf/contrib/pgfplots/.
[Koh15] Markus Kohm. KOMA - Script. version 3.18, July 2, 2015 (or newer).
url: http://mirror.ctan.org/macros/latex/contrib/koma-script/.
[L3Pa] The LATEX3 Project Team. l3kernel. version SVN 6377, Jan. 19, 2016 (or newer).
url: http://mirror.ctan.org/macros/latex/contrib/l3kernel/.
[L3Pb] The LATEX3 Project Team.
l3packages. version SVN 6377, Jan. 19, 2016 (or newer).
url: http://mirror.ctan.org/macros/latex/contrib/l3packages/.
[MS00] Frank Mittelbach and Rainer Schöpf.
amstext. version 2.01, June 29, 2000 (or newer).
url: http://mirror.ctan.org/macros/latex/required/amstext/.
[Rei98] Axel Reichert. nicefrac. version 0.9b, Aug. 4, 1998 (or newer).
url: http://mirror.ctan.org/macros/latex/contrib/units/.
[Tan13] Till Tantau. TikZ/pgf. version 3.0.0, Dec. 13, 2013 (or newer).
url: http://mirror.ctan.org/graphics/pgf/.
[Tel15] Christian Tellechea. chemfig. version 1.2c, Nov. 20, 2015 (or newer).
url: http://mirror.ctan.org/macros/generic/chemfig/.

C. Index

Symbols <- (arrow type) . . . . . . . . . . . . . . . . 23 <==> (arrow type) . . . . . . . . . . . 24, 38

-/> (arrow type) . . . . . . . . . . . . . . . 23 <-> (arrow type) . . . . . . . . . . . . . . . 23 <=> (arrow type) . . . . . . . . . . . . . . . 23
-> (arrow type) . . . . . . . . . . . . . . . . 23 </- (arrow type) . . . . . . . . . . . . . . . 23 <=>> (arrow type) . . . . . . . . . . . . . . 23

39
 INDEX

<=o> (arrow type) . . . . . . . . . . . . . . 23 \DeclareChemAdditionSymbol . . 19 N

<=o>> (arrow type) . . . . . . . . . . . . . 23 \DeclareChemArrow . . . . . . . . . . . . 27 name-format . . . . . . . . . . . . . . . . . . . 30
<> (arrow type) . . . . . . . . . . . . . . . . 23 \DeclareChemBond . . . . . . . . . . . . . 12 name-width . . . . . . . . . . . . . . . . . . . . 30
<o> (arrow type) . . . . . . . . . . . . . . . 23 \DeclareChemBondAlias . . . . . . . . 12 \NewChemAdditionSymbol . . . 19, 38
<<=> (arrow type) . . . . . . . . . . . . . . 23 \DeclareChemCompoundProperty 18 \NewChemArrow . . . . . . . . . . . . . . . 27 f.
<<=o> (arrow type) . . . . . . . . . . . . . 23 \DeclareChemSymbol . . . . . . . . . . . 20 \NewChemBond . . . . . . . . . . . . . . . . 12 f.
== (arrow type) . . . . . . . . . . . . . . . . 23 \NewChemBondAlias . . . . . . . . . . . 12 f.
>=< (arrow type) . . . . . . . . . . . . 23, 38 F \NewChemCompoundProperty . 18, 38
>=<< (arrow type) . . . . . . . . . . . 23, 38 Feuersänger, Christian . . . . . . . 34 \NewChemSymbol . . . . . . . . . . . . 20, 38
>>=< (arrow type) . . . . . . . . . . . 23, 38 font-family . . . . . . . . . . . . . . . . . . . 32 nicefrac (package) . . . . . . . . . . . . . 2, 6
font-series . . . . . . . . . . . . . . . . . . . 32
A font-shape . . . . . . . . . . . . . . . . . . . . 32 O
adduct-penalty . . . . . . . . . . . . . . . 14 font-spec . . . . . . . . . . . . . . . . . . . . . 33 \ox . . . . . . . . . . . . . . . . . . . . . . 8, 21, 24
adduct-space . . . . . . . . . . . . . . 14, 16 fontspec (package) . . . . . . . . . . . . . 33
amsmath (package) . . . . . . . . . . . . . 38 format . . . . . . . . . . . . . . . . . . . . . . . . 31 P
amstext (package) . . . . . . . . . . . . 2, 38 \fplus . . . . . . . . . . . . . . . . . . . . . . . . 10 pgfmanual (manual) . . . . . . . . . . . . 27
arrow-min-length . . . . . . . . . . . . . 25 frac-math-cmd . . . . . . . . . . . . . . 5, 37 pgfplots (package) . . . . . . . . . . . . . . 34
arrow-offset . . . . . . . . . . . . . . . . . . 25 frac-style . . . . . . . . . . . . . . . . . . . 5 f. plus-output-symbol . . . . . . . . 19, 38
arrow-penalty . . . . . . . . . . . . . . . . 26 plus-penalty . . . . . . . . . . . . . . 19, 38
arrow-ratio . . . . . . . . . . . . . . . . . . . 25 H plus-space . . . . . . . . . . . . . . . . . 19, 38
arrow-style . . . . . . . . . . . . . 26 ff., 37 Hensel, Martin . . . . . . . . . . . . . . . . 2 \ProvideChemAdditionSymbol . . 19
arrow-yshift . . . . . . . . . . . . . . . . . . 25 \ProvideChemArrow . . . . . . . . . . . . 27
atom-format . . . . . . . . . . . . . . . . . . . 31 K \ProvideChemBond . . . . . . . . . . . . . 12
Kohm, Markus . . . . . . . . . . . . . . . . . . 2 \ProvideChemCompoundProperty 18
B
KOMA-Script (bundle) . . . . . . . . . . 2 \ProvideChemSymbol . . . . . . . . . . . 20
\bond . . . . . . . . . . . . . . . . . . . . 11 ff.,
17
kroeger-vink . . . . . . . . . . . . . . . . . . 36
bond-length . . . . . . . . . . . . . . . . . 13 f.
kv-neutral-symbol . . . . . . . . . . . . 37 Q
bond-offset . . . . . . . . . . . . . . . . . . . 14
kv-positive-hshift . . . . . . . . . . . 37 “Quantities, Symbols and Units in
bond-penalty . . . . . . . . . . . . . . . . . . 14
kv-positive-offset . . . . . . . . . . . 37 Physical Chemistry”,
bond-style . . . . . . . . . . . . . . . . . . . . 14
kv-positive-radius . . . . . . . . . . . 37 IUPAC Green Book . 5, 11,
C kv-positive-style . . . . . . . . . . . . 36 15
\ce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 kv-positive-vshift . . . . . . . . . . . 37
\ch . . 3–11, 13–22, 24 ff., 28–31, 33 f., R
36 ff. L radical-hshift . . . . . . . . . . . . . . . 14
charge-hshift . . . . . . . . . . 11, 13, 15 l3kernel (bundle) . . . . . . . . . . . . . . . . 2 radical-radius . . . . . . . . . . . . 14, 35
charge-style . . . . . . . . . . . . . . . . . . 14 l3keys2e (package) . . . . . . . . . . . . . . 2 radical-space . . . . . . . . . . . . . . . . 14
charge-vshift . . . . . . . . . . . . . . . . 14 l3packages (bundle) . . . . . . . . . . . . . 2 radical-style . . . . . . . . . . . . . . . . 14
\charrow . . . . . . . . . . . . . . . . . . . . . . 29 label-offset . . . . . . . . . . . . . . . . . . 25 radical-vshift . . . . . . . . . . . . . . . 14
\chcpd . . . . . . . . . . . . . . . . . . . . . . . . 17 label-style . . . . . . . . . . . . . . . . . . . 26 Reichert, Axel . . . . . . . . . . . . . . . . 2
chemfig (package) . . . . . . . . . . . 26, 34 lewis-default . . . . . . . . . . . . . . . . 35 \RemoveChemCompoundProperty . 18
chemformula . . . . . . . . . . . . . . . . . . . . 2 lewis-distance . . . . . . . . . . . . . . . 35 \RenewChemAdditionSymbol . . . . 19
\chemformula@bondlength . . . . . 13 lewis-line-length . . . . . . . . . . . . 35 \RenewChemArrow . . . . . . . . . . . . . 27 f.
\chemsetup . . . . . . . . . . . . . . . . . . 3, 10 lewis-line-width . . . . . . . . . . . . . 35 \RenewChemBond . . . . . . . . . . . . . . . 12
\chlewis . . . . . . . . . . . . . . . . . . . 34–37 lewis-offset . . . . . . . . . . . . . . . . . . 35 \RenewChemCompoundProperty . . 18
\chname . . . . . . . . . . . . . . . . . . . . . . . 30 lppl . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 \RenewChemSymbol . . . . . . . . . . . . . 20
\chstoich . . . . . . . . . . . . . . . . . . . 5, 37
circled . . . . . . . . . . . . . . . . . 10, 14, 38 M S
circletype . . . . . . . . . . . . . 10, 14, 38 math-space . . . . . . . . . . . . . . . . . . . . 22 Schöpf, Rainer . . . . . . . . . . . . . . . . . 2
Cohan, E. Richard . . . . . . . 5, 11, 15 \mch . . . . . . . . . . . . . . . . . . . . . . . . . . 10 scrlfile (package) . . . . . . . . . . . . . . . . 2
compound-sep . . . . . . . . . . . . . . . . . . 25 mhchem (package) . . . . . . . . . 2 f., 22 \setchemformula2, 9 f., 13, 15 ff., 22,
ctan . . . . . . . . . . . . . . . . . . . . . . . 2, 34 minus-output-symbol . . . . . . . 19, 38 32, 34, 36
minus-penalty . . . . . . . . . . . . . 19, 38 \ShowChemArrow . . . . . . . . . . . . . . 27 f.
D minus-space . . . . . . . . . . . . . . . 19, 38 \ShowChemBond . . . . . . . . . . . . . . . . 12
decimal-marker . . . . . . . . . . . . . . 5, 9 Mittelbach, Frank . . . . . . . . . . . . 2 stoich-paren-parse . . . . . . . . . . . . 5

40
 INDEX

stoich-print . . . . . . . . . . . . . . . 5, 37 T tikz-external-disable . . . . 34, 37

Tantau, Till . . . . . . . . . . . . . . . . . . . 2 TikZ/pgf (package) . . . . . . . . . . . . . . 2
stoich-space . . . . . . . . . . . . . . . . . 5 f.
Tellechea, Christian . . . . . . 26, 34
subscript-style . . . . . . . . . . . . . . 13 X
The LATEX3 Project Team . . . . 2 xfrac (package) . . . . . . . . . . . . . . 2, 5 f.
subscript-vshift . . . . . . . . . . 13, 16 tikz (package) . . . . . . . . . . . . . . . . . . . 2 xparse (package) . . . . . . . . . . . . . . . . 2

41