I am a chemistry professor who is finishing semester sequestered because of COVID-19. I bought a Huion 1060+ with the intent of using it write equations/formulas for my students in our online classes. I am not drawing major artwork - just an occasional simple molecular structure.
I know there's an open-source extension to LATEX specifically for chemical formulae - I think it's called chemfig - here's what I just found on quick lookup:
Also, for simple diagrammatic stuff, if you don't feel you need a chemistry formula specific tool, and general graphics / vector drawing works for you, then bear in mind that Inkscape is free and open source.
Chemsketch is free for academic use: https://www.acdlabs.com/resources/freeware/chemsketch/
If you only want to draw them by hand, as you were on a blackboard you can use any simple paint program, there are several free ones.
- *MyPaint https://github.com/mypaint/mypaint/releases
- FireAlpaca https://firealpaca.com/
- MediBang https://medibangpaint.com/
- Krita https://krita.org/
- Gimp https://www.gimp.org/
- PaintNet https://www.getpaint.net/
Take a look at them. They are free so just test them.
- Define a similar-sized canvas on a couple of programs, let's say 1920x1080 or smaller.
- See which one is more intuitive for you, and draws more fluidly with your hardware.
You can save your boards as an archive or simply delete the artboard.
*One detail about MyPaint. It has an "infinite canvas" this is, If you need more space you can simply drag it a little or zoom out and you have now a bigger canvas. It is useful but beware not to create a monster that will paralyze your computer. Zoom out, but remember to zoom in again.
Word and Powerpoint or their free rivals such as LibreOffice or OpenOffice have editors for quite rich formulas. They are very easy, but typographic control in LaTeX style is zero.
Structure diagrams need a drawing program. Office products have something quite clunky but easy to learn. Inkscape is the complex but capable one freebie.
Check this molecule structure editor http://molview.org It exports PNG images and knows nothing if the drawn molecule is possible or not. Read the license carefully to see what you give and promise if you use it.
There are also on-line editors, for instance cactus has both gif and vmrl structure creators.