Editing Atom (section)

=== Valence and bonding behavior ===
{{Main|Valence (chemistry)|Chemical bond}}

Valency is the combining power of an element. It is determined by the number of bonds it can form to other atoms or groups.<ref>{{GoldBookRef|title=valence|file=V06588}}</ref> The outermost electron shell of an atom in its uncombined state is known as the [[valence shell]], and the electrons in
that shell are called [[valence electron]]s. The number of valence electrons determines the [[chemical bond|bonding]]
behavior with other atoms. Atoms tend to [[Chemical reaction|chemically react]] with each other in a manner that fills (or empties) their outer valence shells.<ref name=reusch20070716 /> For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound [[sodium chloride]] and other chemical ionic salts. Many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. Thus, [[chemical bond]]ing between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the [[organic compounds]].<ref name=chemguide />

The [[chemical element]]s are often displayed in a [[periodic table]] that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the [[noble gas]]es.<ref name=husted20031211 /><ref name=baum2003 />