In chemistry, especially organic chemistry, molecules and reactions are usually schematically depicted by Lewis structures which provide a representation that makes it easy to grasp the structure and bonding situation of a molecule. But according to Wikipedia Lewis structures have only been introduced in 1916. What representations have chemists (and other scientists) used prior to 1916 to talk about the structural and electronic changes that molecules undergo during chemical reactions? Was there a generally accepted system or did more or less every scientist have his own style?
I can't leave a comment since I don't have enough rep but I will try to make this an answer.
I know that Robert Robinson was the first to use arrows in electron flow pathways in mechanisms and the convention used for radicals and charges.
I have seen some early drawings of phosphorous-oxygen molecules from around the middle 1860's and they looked pretty much like what we use today except there might of been a different symbol used (but the idea of stoichiometry was there).
This wiki page looks like it might answer your question. Particularly the drawings by Marc Antoine Auguste Gaudin. Before this time you are looking at Dalton's works which seem to be the earliest semblance of modern chemistry.