Chemical element native solid elements occur in alloys, such as that of iron and nickel. The history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulfur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal. Alchemists and chemists subsequently identified many more; all of the naturally occurring elements were known by 1950. The properties of the chemical elements are summarized in the periodic table, which organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share
Extended periodic table recent discovery being that of tennessine in 2010. As some superheavy elements were predicted to lie beyond the seven-period periodic table, an additional eighth period containing these elements was first proposed by Glenn T. Seaborg in 1969. This model continued the pattern in established elements and introduced a new g-block and superactinide series beginning at element 121, raising the number of elements in period 8 compared to known periods. These early calculations failed to consider relativistic effects that break down periodic trends and render simple extrapolation impossible, however. In 1971, Fricke calculated the periodic table up to "Z" = 172,