Periodic table

The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the <a href="/facts/Chemical_element/0jducgWD">chemical elements</a> into rows ("<a href="/facts/Period_(periodic_table)/WpGUFh5V">periods</a>") and columns ("<a href="/facts/Group_(periodic_table)/YGBcUabv">groups</a>"). It is an <a href="/facts/Cultural_icon/r61E5wrT">icon</a> of <a href="/facts/Chemistry/SrNqkGVm">chemistry</a> and is widely used in <a href="/facts/Physics/a7aH2y08">physics</a> and other sciences. It is a depiction of the <a href="/facts/Periodic_trends/dI0mkSju">periodic law</a>, which states that when the elements are arranged in order of their <a href="/facts/Atomic_number/bgAr581S">atomic numbers</a> an approximate <a href="/facts/Periodic_function/Sm8lJQsF">recurrence of their properties</a> is evident. The table is divided into four roughly rectangular areas called <a href="/facts/Block_(periodic_table)/BbzD5jUU">blocks</a>. Elements in the same group tend to show similar chemical characteristics.
Vertical, horizontal and diagonal <a href="/facts/Periodic_trends/dI0mkSju">trends</a> characterize the periodic table. <a href="/facts/Metal/PT8hNX6R">Metallic</a> character increases going down a group and from right to left across a period. <a href="/facts/Nonmetal_(chemistry)/0oejKuzK">Nonmetallic</a> character increases going from the bottom left of the periodic table to the top right.
The first periodic table to become generally accepted was that of the Russian chemist <a href="/facts/Dmitri_Mendeleev/xdouRrx8">Dmitri Mendeleev</a> in 1869; he formulated the periodic law as a dependence of chemical properties on <a href="/facts/Atomic_mass/J1FJY9MV">atomic mass</a>. As not all elements were then known, there were gaps in his periodic table, and Mendeleev successfully used the periodic law to <a href="/facts/Mendeleev%2527s_predicted_elements/C4vgW0uy">predict some properties of some of the missing elements</a>. The periodic law was recognized as a fundamental discovery in the late 19th century. It was explained early in the 20th century, with the discovery of <a href="/facts/Atomic_number/bgAr581S">atomic numbers</a> and associated pioneering work in <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a>, both ideas serving to illuminate the internal structure of the atom. A recognisably modern form of the table was reached in 1945 with <a href="/facts/Glenn_T._Seaborg/w1a3mume">Glenn T. Seaborg</a>'s discovery that the <a href="/facts/Actinide/kHC4lxJV">actinides</a> were in fact f-block rather than d-block elements. The periodic table and law are now a central and indispensable part of modern chemistry.
The periodic table continues to evolve with the progress of science. In nature, only elements up to atomic number 94 exist; to go further, it was necessary to <a href="/facts/Synthetic_element/azU9Nr1m">synthesize</a> new elements in the laboratory. By 2010, the first 118 elements were known, thereby completing the first seven rows of the table; however, chemical characterization is still needed for the heaviest elements to confirm that their properties match their positions. New discoveries will extend the table <a href="/facts/Extended_periodic_table/Q3rg3qLA">beyond these seven rows</a>, though it is not yet known how many more elements are possible; moreover, theoretical calculations suggest that this unknown region will not follow the patterns of the known part of the table. Some scientific discussion also continues regarding whether some elements are correctly positioned in today's table. Many <a href="/facts/Alternative_periodic_tables/xvkrla92">alternative representations</a> of the periodic law exist, and there is some discussion as to whether there is an optimal form of the periodic table.

Periodic table open-in-new

Periodic table