The diagonal relationship between lithium and magnesium
Both metals are harder than their members in the respective groups. For instance, lithium is harder than sodium, potassium, rubidium, and cesium. On the other hand, magnesium is also harder than calcium, strontium, and barium.
Both elements have high melting and boiling points.
Unlike other elements in group 1 and 2, both lithium and magnesium react directly with nitrogen to form nitrides. (Li3N and Mg3N2)
Both compounds of lithium and magnesium are less electropositive and therefore are less stable.
Both magnesium nitrate and lithium carbonate produces lithium oxide and magnesium oxide respectively when heated and also yield nitrogen dioxide and oxygen as shown in the equation below.
4LiNO3→ 2Li2O(s) + 4NO2(g) + O2(g)
Mg(NO3)2(S)→2MgO(s) + 4NO2(g) + O2(g)
A great number of lithium salts such as lithium hydroxide, lithium oxalate, lithium carbonate, and lithium phosphate are sparingly soluble in cold water. The corresponding salts of magnesium show similar properties. On the other hand, the corresponding salts of sodium and potassium are soluble in water.
Both magnesium and lithium halides and alkyles are highly soluble in organic solvents such as alcohol. The corresponding halides and alkyles of sodium and potassium are insoluble in organic solvents.
Both lithium and magnesium chlorides undergo hydrolysis in hot water even if it is partial dissociation. Sodium and potassium chloride does not hydrolyze at all.
All alkali metal sulfates from alumns except lithium sulphate.
Both magnesium and lithium ions and their compounds are highly hydrated than those of other alkali and alkaline earth metals.
Lithium halides, unlike other alkali metal halides, are partially covalent because of the tendency of lithium-ion to attract electron(s) towards its positive nucleus.