superoxides. Li is the only group 1 element which forms a stable nitride, Li3N. Mg, as well as other group 2 elements, also form nitrides. Lithium carbonate, phosphate and fluoride are sparingly soluble in water. The corresponding group 2 salts are insoluble. (Think lattice and solvation energies). Both Li and Mg form covalent organometallic compounds. LiMe and MgMe2 (cf. Grignard reagents) are both valuable synthetic reagents. The other group 1 and group 2 analogues are ionic and extremely reactive (and hence difficult to manipulate). Chlorides of both Li and Mg are deliquescent (absorb moisture from surroundings) and soluble in alcohol and pyridine. Lithium chloride, like magnesium chloride (MgCl2·6H2O) separates out from hydrated crystal LiCl·2H2O. Lithium carbonate and magnesium carbonate are both unstable and can produce corresponding oxides and carbon dioxide when they are heated. Further diagonal similarities have also been suggested for carbon-phosphorus and nitrogen-sulfur, along with extending the Li-Mg and Be-Al relationships down into the transition elements (such as scandium). References Inorganic chemistry Periodic table