11Halides of alkaline earth metals
(1) All beryllium halides are essentially covalent and are soluble in organic solvents. They are hydroscopic and fume in air due to hydrolysis. On hydrolysis, they produce acidic solution.
BeCI2 + 2H2O —→ Be (OH)2 + 2HCI
(2) The halides of all other alkaline earth metals are ionic. Their ionic character, however increases as the size of the metal ion increase.
(3) Except BeCl2 all other chlorides of group 2 form hydrates but their tendency to form hydrates decreases for eg – MgCl2.6H2O, CaCl2.6H2O.
(4) The hydrated chloride, bromides and iodides of Ca, Sr and Ba can be dehydrated on heating but those of Be and Mg undergo hydrolysis.
(5) BeF2 is very soluble in water due to the high hydration energy of the small Be+2 ion. The other fluorides (MgF2, CaF2, SrF2 and BaF2) are almost insoluble in water. Since on descending the group lattice energy decreases more rapidly than the hydration energy. Therefore whatever little solubility these fluorides have that increase down the group.
The chlorides, bromides and iodides of all other elements i.e. Mg, Ca, Sr, Ba are ionic have much lower melting points than the fluorides and are readily soluble in water. The solubility decreases some what with increasing atomic number.
(6) Except of BeCl2 and MgCl2, the other chlorides of alkaline earth metals impart characteristics colour to flame.
CaCl2 = Brick red colour
SrCl2 = Crimson colour
BaCl2 = Grassy green colour
