Editing Electron configuration (section)

=== Periodic table ===
{{Main article|Block (periodic table)}}
[[File:Periodic table blocks spdf (32 column).svg|thumb|upright=1.5|Electron configuration table showing [[Block (periodic table)|blocks]].]]
The form of the [[periodic table]] is closely related to the atomic electron configuration for each element. For example, all the elements of [[alkaline earth metal|group 2]] (the table's second column) have an electron configuration of [E]&nbsp;''n''s{{sup|2}} (where [E] is a [[noble gas]] configuration), and have notable similarities in their chemical properties. The periodicity of the periodic table in terms of [[periodic table block]]s is due to the number of electrons (2, 6, 10, and 14) needed to fill s, p, d, and f subshells. These blocks appear as the rectangular sections of the periodic table. The single exception is [[helium]], which despite being an s-block atom is conventionally placed with the other [[noble gas]]ses in the p-block due to its chemical inertness, a consequence of its full outer shell (though there is discussion in the contemporary literature on whether this exception should be retained).

The electrons in the [[Valence electron|valence (outermost) shell]] largely determine each element's [[Chemical property|chemical properties]]. The similarities in the chemical properties were remarked on more than a century before the idea of electron configuration.{{efn|The similarities in chemical properties and the numerical relationship between the [[atomic weight]]s of [[calcium]], [[strontium]] and [[barium]] was first noted by [[Johann Wolfgang Döbereiner]] in 1817.}}