Answer to Question #21768 in Inorganic Chemistry for ankit

Question

Why the stability of following metal chloride follows the order

LiCl>KCl>NaCl>CsCl

Please explain in detail

Answer 1

The energy released in Step 5 is numerically equivalent (but opposite in sign) to the lattice energy (HoL) for NaCl(s).& The lattice energy (HoL) is defined as the energy required to dissociate a mole of solid ionic compound to gaseous ions (which is the reverse of step 5):
NaCl(s)& -> Na+(g) + Cl-(g); HoL = +771 kJ/mol;
For binary ionic compounds, lattice energy increases as ionic sizes decrease and ionic charges increase. For example, in halides of alkali metals, the trend of lattice energy is as follows:
LiCl > NaCl > KCl > RbCl > CsCl; NaF > NaCl > NaBr > NaI;
The strength of ionic bonds is directly related to the lattice energy and, therefore, is dependent on the ionic charges and ionic sizes, such that greater charges and smaller ionic sizes lead to stronger bonds.
Compounds with high lattice energies also have very high melting points. The melting points of ionic halides increase in the following order:
CsCl < RbCl < KCl < NaCl < LiCl; &
NaCl < MgCl2 < AlCl3;
NaI < NaBr < NaCl < NaF