What is the order of melting point of alkali metal chlorides?
Comparison of melting points of ionic
compounds is generally done by considering the following two factors:
Charge of the cation/anion : More the charge of cation or anion,
stronger will be the forces of attraction between the ions and higher will be
the melting point.
Ionic radii: More the distance between
ions, lesser will be the strength of the bond giving rise to lesser melting
point.
Going by the above rules, the order should
have been: LiCl>NaCl>KCl>RbCl
(Since charges of the ions are same for
each molecule and cationic radius increases down the group.)
But LiCl, due to excessive polarization ,
exhibits high covalent character and is placed last in the order. Hence, the
new order would be:
NaCl>KCl>RbCl>LiCl
The other ions, being similar in size to
chloride ions, do not undergo much polarization.
Comparison of melting points of ionic compounds is generally done by considering the following two factors:
Charge of the cation/anion : More the charge of cation or anion, stronger will be the forces of attraction between the ions and higher will be the melting point.
Ionic radii: More the distance between ions, lesser will be the strength of the bond giving rise to lesser melting point.
Going by the above rules, the order should have been: LiCl>NaCl>KCl>RbCl
(Since charges of the ions are same for each molecule and cationic radius increases down the group.)
But LiCl, due to excessive polarization , exhibits high covalent character and is placed last in the order. Hence, the new order would be:
NaCl>KCl>RbCl>LiCl
The other ions, being similar in size to chloride ions, do not undergo much polarization.
