Lewis acids and bases ionic bonding. Classically, the term "Lewis acid" is restricted to trigonal planar species with an empty p orbital, such as BR where R can be an organic substituent or a halide. For the purposes of discussion, even complex compounds such as EtAlCl and AlCl are treated as trigonal planar Lewis acids. Metal ions such as Na, Mg, and Ce, which are invariably complexed with additional ligands, are often sources of coordinatively unsaturated derivatives that form Lewis adducts upon reaction with a Lewis base[citation needed]. Other reactions might simply be referred to as "acid-catalyzed" reactions. Some compounds, such as HO, are
Chemical nomenclature of technical terms used in chemistry. Similar compendia exist for biochemistry (the "White Book", in association with the IUBMB), analytical chemistry (the "Orange Book"), macromolecular chemistry (the "Purple Book") and clinical chemistry (the "Silver Book"). These "color books" are supplemented by shorter recommendations for specific circumstances that are published periodically in the journal "Pure and Applied Chemistry". The primary function of chemical nomenclature is to ensure that a spoken or written chemical name leaves no ambiguity concerning which chemical compound the name refers to: each chemical name should refer to a single substance. A less important aim is to ensure