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 safety assessment Restriction of Chemical substances) in which hazard and exposure data are considered together to assess the risk of a substance. Chemical safety assessment Chemical safety assessment (CSA) "has to be performed by registrants for substances manufactured and imported in quantities starting at 10 tonnes per year and by downstream users if their uses are not addressed by their supplier," according to REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) legislation. The CSA includes the evaluation of all available relevant information in order to assess risks arising from the manufacture and/or use of a substance. The process needs to be documented