Editing Periodic table (section)

{{Short description|Tabular arrangement of the chemical elements}}
{{About|the table used in chemistry and physics|other uses|Periodic table (disambiguation)}}
{{Featured article}}
{{Pp-move}}
{{Pp|reason=Restoring indefinite semiprotection after full protection expired|small=yes}}
{{Use Oxford spelling|date=September 2024}}
{{Use dmy dates|date=September 2024}}

[[File:Colour 18-col PT with labels.png|thumb|upright=2.2|Periodic table of the chemical elements showing the most or more commonly named [[Names for sets of chemical elements|sets of elements]] (in periodic tables), and a traditional [[dividing line between metals and nonmetals]]. The [[Block (periodic table)#f-block|f-block]] actually fits between [[alkaline earth metals|groups 2]] and [[scandium group|3]]; it is usually shown at the foot of the table to save horizontal space.]]

{{Sidebar periodic table}}
The '''periodic table''', also known as the '''periodic table of the elements''', is an ordered arrangement of the [[chemical element]]s into rows ("[[Period (periodic table)|periods]]") and columns ("[[Group (periodic table)|groups]]"). It is an [[Cultural icon|icon]] of [[chemistry]] and is widely used in [[physics]] and other sciences. It is a depiction of the [[Periodic trends|periodic law]], which states that when the elements are arranged in order of their [[atomic number]]s an approximate [[periodic function|recurrence of their properties]] is evident. The table is divided into four roughly rectangular areas called [[block (periodic table)|blocks]]. Elements in the same group tend to show similar chemical characteristics.

Vertical, horizontal and diagonal [[Periodic trends|trends]] characterize the periodic table. [[Metal]]lic character increases going down a group and from right to left across a period. [[Nonmetal (chemistry)|Nonmetallic]] 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 [[Dmitri Mendeleev]] in 1869; he formulated the periodic law as a dependence of chemical properties on [[atomic mass]]. As not all elements were then known, there were gaps in his periodic table, and Mendeleev successfully used the periodic law to [[Mendeleev's predicted elements|predict some properties of some of the missing elements]]. 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 [[atomic number]]s and associated pioneering work in [[quantum mechanics]], both ideas serving to illuminate the internal structure of the atom. A recognisably modern form of the table was reached in 1945 with [[Glenn T. Seaborg]]'s discovery that the [[actinide]]s 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 <!--THIS IS NOT A TYPO: uranium can fission spontaneously, and when the resulting neutrons strike other uranium atoms in the ore, they can be captured, and the subsequent beta decay produces tiny traces of neptunium and plutonium. See the note--> exist;{{efn|name=transuranium}} to go further, it was necessary to [[synthetic element|synthesize]] new elements in the laboratory. By 2010,<!--THE LAST FOUR WERE *NAMED* IN 2016, BUT ALL WERE ALREADY SYNTHESISED BY 2010--> the first 118 elements were known, thereby completing the first seven rows of the table;<ref>{{Cite web |title=Periodic Table of Elements |url=https://iupac.org/what-we-do/periodic-table-of-elements/ |access-date=11 May 2024 |website=IUPAC {{!}} International Union of Pure and Applied Chemistry |language=en-US}}</ref> however, chemical characterization is still needed for the heaviest elements to confirm that their properties match their positions. New discoveries will extend the table [[extended periodic table|beyond these seven rows]], 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 [[alternative periodic tables|alternative representations]] of the periodic law exist, and there is some discussion as to whether there is an optimal form of the periodic table.