You Must Get The Atoms is a puzzle game created in August 2013 during Ludum Dare 48 about collecting atoms, combining them to make compounds and using those to get through the levels (although if you play it you'll be able to tell that I don't have a chemistry background so some of the compounds do weird things, like CO conducts electricity? I think I confused C and Cu). The main mechanic involves swapping atoms you've collected around so they react with each other.
Playing it now I can see that the timer (there's a ten second timer for each level, as the theme of the game jam was "10 seconds") was very much bolted on and makes the game stupidly difficult, but it still includes some nice touches including a level editor, tutorial throughout the game and actual reasonable collision detection. I also did the music for it, which seems to get annoying after a while but I'm still proud of it.