Editing Period 2 element (section)

{{short description|Any of the chemical elements in the second row of the periodic table}}
{{Periodic table (micro)| title=Period&nbsp;2 in the [[periodic table]] | mark=Li,Be,B,C,N,O,F,Ne}}
{{Sidebar periodic table|expanded=structure }}
A '''period&nbsp;2 element''' is one of the [[chemical element]]s in the second row (or [[Periodic table period|period]]) of the [[periodic table|periodic table of the chemical elements]]. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their [[atomic number]] increases; a new row is started when chemical behavior begins to repeat, creating [[Group (periodic table)|columns]] of elements with similar properties.

The second period contains the elements [[lithium]], [[beryllium]], [[boron]], [[carbon]], [[nitrogen]], [[oxygen]], [[fluorine]], and [[neon]]. In a [[quantum mechanics|quantum mechanical]] description of [[atomic structure]], this period corresponds to the filling of the [[electron shell|second ({{math|1=''n'' = 2}}) shell]], more specifically its [[s-block|2s]] and [[p-block|2p]] subshells. Period&nbsp;2 elements (carbon, nitrogen, oxygen, fluorine and neon) obey the [[octet rule]] in that they need eight electrons to complete their [[valence shell]] (lithium and beryllium obey [[duet rule]], boron is [[Electron deficiency|electron deficient]].), where at most eight electrons can be accommodated: two in the 2s orbital and six in the 2p subshell.