Chem Lib is a simple mod that adds plenty of chemistry related items including:
All 118 elements
Ingots for all elements that make sense (i.e. all except for gases, mercury, iron, gold, etc)
Several dozen chemical compounds, including several "drugs" that have potion effects when consumed
All of the contents of this mod were originally included in the 1.12.2 version of Alchemistry, but it has been split up so it can be used by Alchemistry, Techemistry (Coming soon?), or by modpack makers without necessarily needing to include any other baggage.