Icon of chemistry: the periodic system of chemical elements in the new century.

A closer look: A deeper theoretical understanding of the multifaceted periodic system of elements (PSE) has been achieved in recent years. The large energy gaps above the noble gas shells 1s(2) and np(6) (n=2-6) impress periodicity onto the whole PSE, which is complete with Period 7. The electron configurations of unbound atoms are chemically misleading. The common n+l rule is an example of the "invention of facts" even in the hard sciences.