" appears to refer to a book related to the show 

, rather than a specific episode with that title. There is no specific episode titled "The Periodic Table Explained", however, the scientific nature of the show often uses scientific concepts as key plot points. While there is no episode titled "The Periodic Table Explained", the scientific nature of the show often uses scientific concepts as key plot points. Sherlock Holmes and Joan Watson frequently employ scientific principles, including chemistry, in their investigative methods. The periodic table's use as an organizational "cheat sheet" for chemical properties aligns with Sherlock's deductive reasoning.