Editing Chemical element (section)

==== General chemical symbols ====
There are also symbols in chemical equations for groups of elements, for example in comparative formulas. These are often a single capital letter, and the letters are reserved and not used for names of specific elements. For example, "'''X'''" indicates a variable group (usually a halogen) in a class of compounds, while "'''R'''" is a [[Radical (chemistry)|radical]], meaning a compound structure such as a hydrocarbon chain. The letter "'''Q'''" is reserved for "heat" in a chemical reaction. "'''Y'''" is also often used as a general chemical symbol, though it is also the symbol of [[yttrium]]. "'''Z'''" is also often used as a general variable group. "'''E'''" is used in organic chemistry to denote an [[Polar effect|electron-withdrawing group]] or an [[electrophile]]; similarly "'''Nu'''" denotes a [[nucleophile]]. "'''L'''" is used to represent a general [[ligand]] in [[inorganic chemistry|inorganic]] and [[organometallic chemistry]]. "'''M'''" is also often used in place of a general metal.

At least two other, two-letter generic chemical symbols are also in informal use, "'''Ln'''" for any [[lanthanide]] and "'''An'''" for any [[actinide]]. "'''Rg'''" was formerly used for any [[rare gas]] element, but the group of rare gases has now been renamed [[noble gas]]es and "'''Rg'''" now refers to [[roentgenium]].