Briefly, you can draw virtually any structure with chemfig (given you have enough time).
It's a $\mathrm\LaTeX$ package by Christian Tellechea (profile at CTAN, profile at TeX.SE).
Since it works nicely with another package, TikZ, the aforementioned drawing capabilities can be extended beyond generic chemical formulas.
You can also develop your own styles and keep settings within \setchemfig{…} as separate *.sty files and load the one you need.
Specifically for Lewis structures it used to offer specific \lewis macro; these days it's being replaced with \charge macro.
I'd prefer not to leave an URL with a hardcoded page number of the manual since it appears that the package undergoes rapid development and things may change in the nearest future.
A linear Lewis dot molecular structure can be drawn by exploiting mhchem in conjunction with \underset{…}{…} and \overset{…}{…} like such:
$$
\left[
\ce{
:\!\overset{\Large\cdot\cdot}{\underset{\Large\cdot\cdot}{Cl}}-\overset{\Large\cdot\cdot}{\underset{\Large\cdot\cdot}{O}}\!:
}
\right]^-
$$
$$
\left[
\ce{
:\!\overset{\Large\cdot\cdot}{\underset{\Large\cdot\cdot}{Cl}}-\overset{\Large\cdot\cdot}{\underset{\Large\cdot\cdot}{O}}\!:
}
\right]^-
$$
This is by no means a proper reliable method, but so far it seems to work for simple cases.
