Lewis acids and bases studied chemical bonding. In 1923, Lewis wrote "An acid substance is one which can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms." The Brønsted–Lowry acid–base theory was published in the same year. The two theories are distinct but complementary. A Lewis base is also a Brønsted–Lowry base, but a Lewis acid doesn't need to be a Brønsted–Lowry acid. The classification into hard and soft acids and bases (HSAB theory) followed in 1963. The strength of Lewis acid-base interactions, as measured by the standard enthalpy of formation of an adduct
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