Periodic table been slowly expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behaviour. The modern periodic table now provides a useful framework for analyzing chemical reactions, and continues to be widely used in chemistry, nuclear physics and other sciences. All the elements from atomic numbers 1 (hydrogen) through 118 (oganesson) have been either discovered or synthesized, completing the first seven rows of the periodic table. The first 98 elements exist in nature, although some are found only in trace amounts and others were synthesized in laboratories before being
Alternative periodic tables extended periodic table, suggested by Glenn T. Seaborg in 1969, yet unknown elements are included up to atomic number 218. Theoretical periods above regular period 7 are added. In the research field of superatoms, clusters of atoms have properties of single atoms of another element. It is suggested to extend the periodic table with a second layer to be occupied with these cluster compounds. The latest addition to this multi-story table is the aluminium cluster ion , which behaves like a multivalent germanium atom. Alternative periodic tables Alternative periodic tables are tabulations of chemical elements differing significantly in their organization