<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> An acid is a molecule or ion capable of donating a hydron (proton or hydrogen ion H), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid). </P> <P> The first category of acids is the proton donors or Brønsted acids . In the special case of aqueous solutions, proton donors form the hydronium ion H O and are known as Arrhenius acids . Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents . A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H . </P>

An acid is any solution that has free