BKChem

BKChem is a multiplatform vector drawing application that allows you to create a representation of the chemical bonds that form a determined substance.

It contains a series of templates to simplify your task. Certain chemical compounds, like benzene and purina, already have models built into BKChem, so you don't always have to start from scratch.

You'll draw the bonds one by one. The length and angle of each bond are restricted to make it easier to edit the schematics. BKChem supports the use of linear formulas, charges, and radicals.

You can export your work as a SVG, ODF, PNG, PDF, or OpenOffice file, among others.