Write a note on halides of alkali metal elements and their physical properties.

(N/A) The alkali metal halides,$MX$ (where $X = F, Cl, Br, I$),are all high-melting,colourless crystalline solids.
They 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 $(\Delta_{f} H^{\ominus})$.
The $\Delta_{f} H^{\ominus}$ values for fluorides become less negative as we go down the group,while the reverse is true for $\Delta_{f} H^{\ominus}$ for chlorides,bromides,and iodides.
For a given metal,$\Delta_{f} H^{\ominus}$ always becomes less negative from fluoride to iodide.
The melting and boiling points follow the trend: $Fluoride > Chloride > Bromide > Iodide$.
All these halides 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 the smaller hydration enthalpy of its two ions.
Other halides of lithium are soluble in ethanol,acetone,and ethyl acetate; $LiCl$ is also soluble in pyridine.