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mhchem

mhchem writes chemistry the way chemists write it: \ce{H2SO4} rather than \mathrm{H_2SO_4}. Inside \ce, numbers after an element are subscripts, charges go up, and -> is a reaction arrow; \pu does the same for physical units. The editor below has the chemistry panels — mhchem's and chemfig's — with the maths a chemist needs around them. Click any example on this page to open it there.

Adding mhchem to your page

In fxTeX Pro, name mhchem when you render the page:

fxTeXPro.ready.then(() => {
  fxTeXPro.unlock('fx_pk_your-key-here');
  fxTeXPro.autoRender({ packages: ['mhchem'] });
});

In the equation editor, name it to EqEditor.init() and add its panels to the toolbar. This is the editor above, with chemfig as well:

<script src="https://fxeditor.codecogs.com/fxeditor.api.min.js"></script>

<div id="toolbar"></div>
<div id="mathview"></div>
<div id="latex"></div>

<script>
  const ready = EqEditor.init({
    licence: 'fx_pk_your-key-here',
    packages: ['mhchem', 'chemfig']
  });

  const toolbar = EqEditor.Toolbar.link('toolbar', [
    ['mhchem', 'mhchem_arrows', 'chemfig', 'chemfig_ext', 'arrows'],
    ['operators_core', 'subsupset', 'brackets', 'greeklower', 'greekupper', 'symbols', 'spaces']
  ]);

  ready.then(() => {
    const latex = EqEditor.LaTeXView.link('latex');
    const mathview = EqEditor.MathView.link('mathview').addLaTeXView(latex);
    toolbar.addLaTeXView(latex).addMathView(mathview);
    mathview.setLatex('\\ce{2H2 + O2 -> 2H2O}');
  });
</script>

The mhchem panel has charges, isotopes, oxidation states, precipitates, gases and bonds; mhchem_arrows has the reaction arrows, with room for conditions above and below. Both write inside \ce{}, and add it only when the caret is not in one already. See Using packages for more on both steps.

Formulae and charges

Write a formula as it reads. A number after an element or a bracket is a subscript; a charge at the end goes up, with or without a ^.

\ce{H2O}

H_{2} O

The 2 is a subscript.

\ce{Sb2O3}

{Sb}_{2} O_{3}

Element symbols are upright, not italic.

\ce{H+}

H^{+}

A charge at the end is a superscript.

\ce{CrO4^2-}

Cr O_{4}^{2 -}

Subscript and charge together, stacked.

\ce{[AgCl2]-}

{[Ag {Cl}_{2}]}^{-}

Complexes in square brackets.

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

{[Cu {(N H_{3})}_{4}]}^{2 +}

Groups nest.

\ce{Y^99+}

Y^{99 +}

Multi-digit charges need only the ^.

Stoichiometric numbers

A number in front of a formula is its coefficient, and stays full size. Fractions and decimals work too.

\ce{2H2O}

2 H_{2} O

No space needed after the number.

\ce{0.5H2O}

0.5 H_{2} O

A decimal coefficient.

\ce{1/2H2O}

\frac{1}{2} H_{2} O

A fraction, set small.

Isotopes and nuclides

Mass and atomic numbers go before the symbol, as a superscript and a subscript, and line up on the left.

\ce{^{227}_{90}Th+}

{}_{90}^{227}{Th}^{+}

Mass number above, atomic number below.

\ce{^{0}_{-1}n^{-}}

{}_{- 1}^{0}{n^{-}}

Prescripts and a charge on the same symbol.

Oxidation states and radicals

Roman numerals in a superscript are oxidation states; a dot in one is a radical.

\ce{Fe^{II}}

{Fe}^{II}

An oxidation state.

\ce{Fe^{II}Fe^{III}2O4}

{Fe}^{II} {Fe}^{III} 2 O_{4}

Mixed oxidation states in one formula.

\ce{OCO^{.-}}

O C O^{• -}

A radical anion.

States of matter

A state in brackets after a formula is set as a subscript-sized label.

\ce{H2O(l)}

H_{2} O (l)

Liquid.

\ce{NaCl(s)}

Na Cl (s)

Solid.

\ce{CO2(g)}

C O_{2} (g)

Gas.

\ce{NaOH(aq,$\infty$)}

Na O H (aq, \infty)

Maths inside the state, between $ signs.

Reaction arrows

Arrows are written with -, <, > and =, with a space on each side, and stretch to fit anything written over them.

\ce{A -> B}

A \overset{}{\to} B

Reaction.

\ce{A <- B}

A \overset{}{\leftarrow} B

Reverse reaction.

\ce{A <-> B}

A \overset{}{\leftrightarrow} B

Resonance.

\ce{A <--> B}

A \overset{}{⟷} B

Forward and back, two arrows.

\ce{A <=> B}

A \overset{}{⇌} B

Equilibrium.

\ce{A <=>> B}

A \overset{}{\overset{}{⇀} ↽} B

Equilibrium lying to the right.

\ce{A <<=> B}

A \overset{}{⇀ \overset{}{↽}} B

Equilibrium lying to the left.

\ce{N2 + 3H2 <=> 2NH3}

N_{2} + 3 H_{2} \overset{}{⇌} 2 N H_{3}

A whole equation: + with spaces round it is a plus sign.

Conditions on arrows

Text in square brackets after an arrow goes above it, and a second pair below. It is read as chemistry; put text in braces, and maths between $ signs.

\ce{A ->[H2O] B}

A \overset{H_{2} O}{\to} B

A reagent above the arrow.

\ce{A ->[{text above}][{text below}] B}

A \to_{text below}^{text above} B

Text above and below.

\ce{A ->[$x$][$x_i$] B}

A \to_{x_{i}}^{x} B

Maths above and below.

\ce{Hg^2+ ->[I-] HgI2 ->[I-] [Hg^{II}I4]^2-}

{Hg}^{2 +} \overset{I^{-}}{\to} Hg I_{2} \overset{I^{-}}{\to} {[{Hg}^{II} I_{4}]}^{2 -}

A sequence of reactions.

Precipitates and gases

A v on its own is a precipitate, an arrow down; a ^ on its own is a gas given off, an arrow up.

\ce{SO4^2- + Ba^2+ -> BaSO4 v}

S O_{4}^{2 -} + {Ba}^{2 +} \overset{}{\to} Ba S O_{4} ↓

Barium sulfate precipitates.

\ce{x Na(NH4)HPO4 ->[\Delta] (NaPO3)_x + x NH3 ^ + x H2O}

x Na (N H_{4}) H P O_{4} \overset{Δ}{\to} {(Na P O_{3})}_{x} + x N H_{3} ↑ + x H_{2} O

Ammonia given off, and a variable coefficient.

Bonds

Between two atoms, -, = and # are single, double and triple bonds. \bond{} draws these and the rest by name. For structures in two dimensions, use chemfig.

\ce{A-B=C#D}

A - B = C \equiv D

Single, double and triple.

\ce{CH3-CH=CH2}

C H_{3} - C H = C H_{2}

Propene.

\ce{A\bond{~}B\bond{~-}C}

A \sim B ≃ C

Delocalised bonds.

\ce{A\bond{...}B\bond{....}C}

A \dots B \dots C

Dotted bonds.

\ce{A\bond{->}B\bond{<-}C}

A \to B \leftarrow C

Dative bonds.

Addition compounds

A full stop or an asterisk between two formulae is a centred dot.

\ce{CuSO4.5H2O}

Cu S O_{4} \cdot 5 H_{2} O

A hydrate.

\ce{KCr(SO4)2*12H2O}

K Cr {(S O_{4})}_{2} \cdot 12 H_{2} O

The asterisk works the same way.

Chemistry and maths together

\ce can go anywhere in an equation, and maths can go inside \ce between $ signs.

K_a = \frac{[\ce{H3O+}][\ce{A-}]}{[\ce{HA}]}

K_{a} = \frac{[H_{3} O^{+}] [A^{-}]}{[H A]}

An equilibrium constant: \ce inside a fraction.

\ce{2H2 + O2 -> 2H2O} \quad \Delta H = \pu{-572 kJ}

2 H_{2} + O_{2} \overset{}{\to} 2 H_{2} O Δ H = - 572 kJ

A reaction and its enthalpy.

\ce{CH4 + 2 $\left( \ce{O2 + 79/21 N2} \right)$}

C H_{4} + 2 (O_{2} + \frac{79}{21} N_{2})

Maths inside \ce, and \ce inside that.

Physical units

\pu sets a number and its units: upright units, a thin space between them, and exponents written plainly. A space, or *, between units is a multiplication; / is a fraction and // a slash.

\pu{123 kJ}

123 kJ

A number and its unit.

\pu{123 mm2}

123 {mm}^{2}

A number after a unit is its power.

\pu{123 kJ mol-1}

123 kJ {mol}^{- 1}

Negative powers.

\pu{123 kJ/mol}

123 kJ / mol

As a fraction.

\pu{123 kJ//mol}

123 \frac{kJ}{mol}

With a slash.

\pu{1.2e3 kJ}

1.2 \times 10^{3} kJ

Scientific notation.

\pu{25 °C}

25 °C

Degrees.

R = \pu{8.314 J K-1 mol-1}

R = 8.314 J K^{- 1} {mol}^{- 1}

Inside an equation.

The mhchem manual

This page covers what most chemistry needs. mhchem itself is by Martin Hensel; its manual covers every part of the syntax:

mhchem manual (PDF) — the LaTeX package's documentation, on CTAN.

mhchem on CTAN — the package, its licence and versions.

chemfig — structural formulae and reaction schemes.

Using packages — turning packages on, and their panels.

Supported commands — every chemistry command fxTeX reads.

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