Donaldson R F Periodic Table Lookup
Explore all 118 elements. Click one, or search by name, symbol or atomic number, to see its details.
About this table
Elements are arranged by atomic number (the number of protons) into 7 periods (rows) and 18 groups (columns). Elements in the same group have similar chemistry because they have the same number of outer electrons. The lanthanoids and actinoids are shown in the two rows below the main table.
Atomic masses are the standard atomic weights rounded to at most 5 significant figures; for elements with no stable isotope the mass number of the longest-lived isotope is given. Electron configurations are ground-state configurations in noble-gas shorthand; those for elements above 103 are predicted rather than measured. To work out the mass of a whole compound, use the molar mass calculator.