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 .