Erbium (pronounced /ˈɝbiəm/) is an element on the periodic table. Its symbol is Er. Its atomic number is 68 which means it has 68 protons in an atom. It is a lanthanide and, along with yttrium, terbium, and ytterbium, is one of the four elements to be named after the town of Ytterby in Sweden, all of which are rare earth elements. view more...