Question

What is the order of melting point of alkali metal chlorides?

Answer 1

Alkali metals have one valence electron, outside the noble gas core. The loosely held s-electron in the outermost valence shell of these elements makes them the most electropositive metals. Alkali metal halides are all high melting, colorless crystalline solids.

Complete Solution:
Let us discuss about alkali metal halides in detail:
Alkali metal halides can be prepared by the reaction of the appropriate oxide,hydroxide or carbonate with aqueous hydrohalic acid(HX).All of these halides have high negative enthalpies of formation.
Order of enthalpy of formation: Fluoride>chloride>bromide>iodide.This fluoride are the most stable halides.
The melting and boiling always follow the trend :Fluoride>chloride>bromide>iodide.

**So our answer is $LiCl > NaCl > KCl > RbCl > FrCl > MgC{l_2}$.

Additional Information:**
Alkali metal are soluble in water.The low solubility of LiF in water is due to its high lattice enthalpy whereas the low solubility of CsI is due to smaller hydration enthalpy of its two ions.Other halides are soluble in ethanol, acetone and ethyl acetate; LiCl is soluble in pyridine also.
All of these halides have high negative enthalpies of formation; the ${\vartriangle _f}{H }$ for chlorides, bromides and iodides. For a given metal ${\vartriangle _f}{H}$ always becomes less negative from fluoride to iodide.

Note:
LiCl is deliquescent and crystallises as a hydrate, $LiCl. 2{H_2}O$whereas other alkali metal chlorides do not form hydrates.$LiCl$ and $MgC{l_2}$ are soluble in ethanol.