General:
* Substances
* Compounds
* Elements
* Ingredients
* Materials
* Reagents
* Constituents
More specific:
* Synthetics (for man-made chemicals)
* Toxins (for harmful chemicals)
* Poisons (for highly toxic chemicals)
* Additives (for chemicals added to other substances)
* Solvents (for chemicals used to dissolve other substances)
* Reactants (for chemicals involved in a chemical reaction)
Figurative:
* Elixirs (for magical or powerful chemicals)
* Potions (for concoctions, often with negative connotations)
The best synonym for "chemicals" will depend on the specific context and the intended meaning.