Acid-base chemistry
Several nonmetal halides and oxides are Lewis acids. This is not so while an element has its maximum probable steric number (example CF4, NF3 or SF6) but otherwise acidity usually increases with oxidation state. Such type of compounds react with water to provide oxoacids, that together with the salts derived from them are general compounds of several nonmetals. Compounds along with lone-pairs are potential Lewis bases, base strength failing with group number (15>16>17). In combination through 'hard' acceptors the donor strength fall down a group (example N» P>As) but with 'soft' acceptors the trend might be opposite.
Ion-transfer reactions provide a wide range of complex ions, including ones created from proton transfer (example NH4+ , H3O +, NH2-and OH-), halide complexes (example [PC14]+, [SF5]-), and oxoanions and cations (example SO4 2- , NO2 +). Such type of ions are created in suitable polar solvents and are also well-known in solid compounds. The trends in Brønsted acidity of oxoacids and hydrides in water are explained in Topic E2. pKa values of oxoacids may vary markedly down a group like the structure changes (example HNO3 is a strong acid, H3PO4 a weak acid; the elements Sb, I and Te in period 5 create octahedral species like [Sb(OH)6]-, that are much weaker acids). Brønsted basicity of compounds with lone pairs follows the 'hard' sequence that is discussed above (example NH3>H2O>HF, and NH3»PH3> AsH3).