Periodic table of the chemical elements. Modern periodic table showing 118 elements from hydrogen to oganesson. The periodic table shows the chemical elements ordered by atomic number (number of protons in the nucleus), but arranged in rows (periods) so that elements with similar chemistry occur in the same vertical column (group). The standard periodic table has 118 elements arranged in 18 groups and 7 periods. Each element is represented by its chemical symbol. Above each symbol is the element's atomic number, and below it is the element's name. The lathanides and actinides are expanded at bottom.