How to get this dot in the picture?
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3Is it \bullet...?– Najib IdrissiFeb 5, 2014 at 20:02
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Thank you for your answer! I made your comment answer and mentioned you so I remember this later too.– Léo Léopold Hertz 준영Feb 5, 2014 at 20:06
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@cgnieder The symbol looks like this dl.dropboxusercontent.com/u/62073194/… in the first package. I think bullet is better.– Léo Léopold Hertz 준영Feb 5, 2014 at 22:55
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@Masi: I did. You get no satisfying results first, but you can click on “Select from the complete list!” and then you get good results, among others of course.– SperavirFeb 5, 2014 at 22:56
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@cgnieder: But the question is asked in a wrong way IMHO.– SperavirFeb 5, 2014 at 23:05
2 Answers
R. Schumacher already answered what the symbol means. How to get it with LaTeX is a different question. Here are five different versions all of which don't look perfect in the default settings:
\documentclass{article}
\usepackage{chemformula,mhchem,array}
\newcommand*\cs[1]{\texttt{\textbackslash#1}}
\begin{document}
\newcounter{version}
\setlength\extrarowheight{2pt}
\begin{tabular}{>{\stepcounter{version}\theversion.\quad}ll}
. & $\mathrm{O}_2^{.-}$ \\
\cs{cdot} & $\mathrm{O}_2^{\cdot-}$ \\
\cs{bullet} & $\mathrm{O}_2^{\bullet-}$ \\
mhchem & \ce{O2^{.-}} \\
chemformula & \ch{O2^{.-}} \\
\end{tabular}
\end{document}
To me version 3. clearly is much too big to look good and not an option. Versions 1. and 2. are arguably too small although \cdot
doesn't look too bad in my opinion. In the mhchem
version the dot and the minus sign are very close while in the chemformula
version they're not perfectly aligned. I prefer the chemformula
version nonetheless because it is adjustable:
\documentclass{article}
\usepackage{chemformula}
\begin{document}
\ch{O2^{.-}}
\setchemformula{radical-radius=1pt}
\ch{O2^{.-}}
\setchemformula{
radical-radius=.5pt ,
radical-vshift=.444ex
}
\ch{O2^{.-}}
\end{document}
That symbol when used in Chemistry (usually with the full bonds between atoms) denotes an extra free electron (it negative charge). The minus is actually saying it twice.
These are usually used in Lewis Dot Structures (Diagrams) and mean a free electron (unbonded). Lewis Structure
Or when you see this you are describing an Oxygen radical (ie negative charge).
Also this entire area of notation is very much author and sub discipline dependent, so you need to verify exactly what the author/discipline in meaning in that context.
And as the preceding offered you would just use \bullet.
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Very good addition! I have used convention that the bullet says if the species is radical and the number there says how much charged. Feb 5, 2014 at 20:19
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2I have to disagree that "The minus is actually saying it twice", and it's misleading to say that "an extra free electron" is synonymous with "a negative charge". While there's arguably a degree of tautology (some might say 'precision') in writing $\ce{O2^{.-}}$ -- as an $\ce{O2}$ radical will always have a negative charge, and a negatively charged $\ce{O2}$ will always be a radical -- the two things are by no means synonymous. In other species, for instance atomic oxygen, a lone oxygen atom, $\ce{O^{.}}$ has no charge, while an oxygen ion, $\ce{O-}$ is not a radical. Sep 20, 2017 at 14:22
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(Please excuse mhchem notation in the above comment. I forgot that I wasn't on Chemistry StackExchange.) Sep 20, 2017 at 14:25
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An extra free electron, by no means, denotes directly a "negative charge". For example, the isopropyl radical (CH₃C•HCH₃) is neutral, not "negatively charged". Radicals that do have a negative charge are commonly called radical anions. Completely agreed with @owjburnham. Aug 14, 2021 at 2:09