hydrogen Search Term: HydrogenSource Category: ASSISTHydrogen is the chemical element with the symbol H. It has the atomic number 1. It is a member of group 1 on the periodic table and is categorised as a diatomic nonmetal. Synonyms: hydrogen gas; CAS Number: 1333-74-0; Signal Word: Danger. Tags: H1333-74-0hydrogen gaselement 1