Chemistry

The chem package adds chemical reaction equations and 2D structure drawings. Load it with:

\use{chem}

Reaction equations

\ce typesets a reaction from a compact, mhchem-style notation — and like mhchem it sets the result inline, flowing in the running text:

Methane burns: \ce{CH4 + 2 O2 -> CO2 + 2 H2O}.

Species are separated by spaces. Within a species, a run of letters is an element symbol (set upright), a digit run after letters is a subscript count, and a leading number is a stoichiometric coefficient (set full size, with a thin space before its species). The operator + and the arrows are math symbols, so they get the proper math spacing.

Arrow tokens: -> (reaction), <=> (equilibrium), <-, <->. To show a reaction centered on its own line, wrap it (at a larger size if you like) in \centerline:

\centerline{\font lmroman 14 regular \ce{CH4 + 2 O2 -> CO2 + 2 H2O}}

\ce is a pure document-language macro, not a built-in: it parses the notation and emits math markup that ordinary math mode renders. Neutral species are fully supported; for an ion, write the charge with \up outside \ce (a ^ cannot pass through a macro argument).

Formula helpers

For a formula in running prose without \ce, the helpers set counts and charges directly:

a litre of H\dn{2}O        % subscript
the ion Na\up{$+$}         % superscript charge
sulfate SO\dn{4}\up{$2-$}

\dn and \up are the chemistry-friendly names for the engine’s \textsub / \textsup.

Structure drawings

Over the vector-graphics layer, chem draws skeletal structures from named coordinates: \atom{name}{x y}{label} places and labels an atom, and \bond, \dbond, \tbond draw single, double, and triple bonds between two named atoms, shortened at each end so the labels stay clear.

\picture width:2in height:1in {
  \atom{c}{0.4in 0.5in}{C}
  \atom{o}{1.4in 0.5in}{O}
  \dbond{c}{o}
}

Bond geometry is tunable through bondgap (the clearance at each end) and doublesep (half the gap between the two lines of a double bond).