A
period 6 element is one of the
chemical elements in the sixth row (or
period) of the
periodic table of the elements, including the
lanthanides. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The sixth period contains 32 elements, tied for the most with
period 7, beginning with
caesium and ending with
radon.
Lead is currently the last stable element; all subsequent elements are
radioactive, however
bismuth has a half-life of more than 10
19 years, more than 1,000 times longer than the current age of the universe. As a rule, period 6 elements fill their 6s
shells first, then their 4f, 5d, and 6p shells, in that order, however there are exceptions, such as
cerium.