Hydrogen: the first chemical element on the periodic table, it is the lightest element with atomic number 1 and symbol H. Its most common isotope, protium, consists of one proton and one electron, making it the simplest isotope.
Hydrogen: the first chemical element on the periodic table, it is the lightest element with atomic number 1 and symbol H. Its most common isotope, protium, consists of one proton and one electron, making it the simplest isotope.