Period 1 elements
Period 1 contains just two elements: hydrogen and helium. Both have only one electron shell (the 1s orbital), making them unique on the periodic table - hydrogen sits as a nonmetal and helium as a noble gas.
Period 1 contains just two elements: hydrogen and helium. Both have only one electron shell (the 1s orbital), making them unique on the periodic table - hydrogen sits as a nonmetal and helium as a noble gas.