Chemically, they are characterised-to varying degrees-by covalent bonding tendencies, basic or amphoteric oxides 7 and the formation, in solution, of cations, hydroxocations, or cations and oxyanions. They can also form Zintl phases (halfmetallic compounds formed between highly electropositive metals and moderately electronegative metals or metalloids). The oxides are ionic; some are glass formers ; and those of Cd, Hg, In, Tl and Bi are predominately basic, with the remainder amphoteric. The lower chlorides 8 are typically ionic, involatile, insoluble in organic solvents, and water-soluble; higher chlorides tend to be more covalent, volatile, soluble in organic solvents, and susceptible to hydrolysis.