# Proper dash to use for negative charge

What type of dash does one use when indicating something like F$^{-}$? I assumed it was a minus, since you indicate positive charge with a +, but there is one professor I know who insists that it should be typeset with an endash. Is there a style manual on chemical typesetting I can consult.

• Say for instance in Microsoft Word, if you compare the minus sign from the table of symbols (which is the correct symbol) to a hyphen, an en dash, and an em dash. You may find it quite difficult to distinguish between the legitimate minus symbol and the en dash. The hyphen and the em dash easily look like sloppy choices for an alternative. Feb 5 at 22:32

[…] one professor I know who insists that it should be typeset with an en dash.

I disagree! A standard minus sign should be

• on the same height as the horizontal line of a plus sign;
• as long as an equal sign.

The en dash is

• lower than the horizontal bar of the plus sign;
• slightly longer than the equal sign.

Unicode has dedicated characters for minus and superscript minus

• standard minus: U+2212: −
• superscript minus: U+207B: Cl⁻

The situation, and how to realize the correct typography using $$\mathrm\LaTeX$$ has been described in the German article Feinheiten bei wissenschaftlichen Publikationen – Mikrotypographie-Regeln, Teil II by Marion Neubauer in Die TeXnische Kommödie, 1997, 1, 25-44 (PDF).
• @Canageek In $\LaTeX$, things are easy :) Within equations in math mode, a - is automatically rendered in the right length and with the right vertical position. The same is true for a superscripted minus within a \ce{...} expression. Apr 20 '15 at 19:55
• @Canageek To quote the Red Book (Nomenclature of Inorganic Chemistry) by the International Union of Applied Chemistry (IUPAC), rule IR 2.3.2 "Plus and minus signs" their statement is: "The signs $+$ and $-$ are used to indicate the charge on an ion in a formula or name. Compare with this old.iupac.org/publications/books/rbook/Red_Book_2005.pdf, page 25. Not a iota of "dash". Apr 21 '15 at 8:26