d) Reaction with halogens: The members of the family combine with halogen to form corresponding halides which are ionic crystalline solids.
Reactivity of alkali metals with particular halogen increases from Li to Cs.
e) Reaction with water: Alkali metals react with water and other compounds containing acidic hydrogen atoms such as hydrogen halides, acetylene etc. to liberate hydrogen gas.
f) Solubility in liquid ammonia: All alkali metals dissolve in liquid ammonia giving deep blue solutions which are conducting in nature.
g) Reaction with sulphur and phosphorus: Alkali metals react with sulphur and phosphorus on heating to form sulphides and phosphides respectively.
Diagonal relationship between Li and Al
Li resembles Mg mainly due to similarity in sizes of their atoms and ions. The main points of similarity are:
i) Both are quite hard. ii) Both LiOH and Mg( OH) 2 are weak bases.
iii) Carbonates of both on heating decompose to produce oxides and carbondioxide.
iv) Both react with nitrogen to give ionic nitrides. v) Nitrates of both decompose on heating to give oxides. vi) Both Li and Mg do not form solid bicarbonates. vii) Because of covalent character LiCl and MgCl2 are soluble in ethanol.
viii) The hydroxides, bicarbonates and fluorides of both Li and Mg are sparingly soluble in water.