Question

Arrange the following in increasing order of lattice energy:
A.$\;LiI < LiBr < LiCl < LiF\,$
B.$\,LiF < LiBr < LiCl < LiI\,$
C.$\,LiF < LiCl < LiBr < LiI\,$
D.None of these

Answer 1

Lattice Energy is a form of mechanical energy and is defined as the energy which is required to break an ionic compound into its constituent gaseous ions. Stronger the bond ,more will be the lattice energy.

Complete step by step answer:
The lattice energies of ionic compounds are relatively large. The lattice energy of $\,NaCl\,$, as an example, is $\,787.3\,$ kJ/mol, which is merely slightly but the energy given off when gas burns. The bond between ions of opposite charge is strongest when the ions are small. The lattice energies for the metal halides is therefore largest for $\,LiF\,$ and smallest for $\,CsI\,$. The strength of the bond between the ions of opposite charge in an ionic compound therefore depends on the fees on the ions and therefore the distance between the centers of the ions once they pack to create a crystal. An estimate of the strength of the bonds in an ionic compound may be obtained by measuring the lattice energy of the compound, which is the energy given off when oppositely charged ions within the gas phase close to create a solid.
So, the lattice energy of lithium halides ($\,LiF,{{ }}LiCl,{{ }}LiBr,{{ }}Li\,$) are increased from top to bottom i.e from $\,LiF\,$to $\,LiI\,$ because of increase in size of the halides. Because the size of the halide increases, it requires more energy to mix them together and releases more energy once they are softened. Smaller the scale of anion, lesser is its polarization, more is ionic nature, more is lattice energy.
So, the proper order of lattice energy is B.

Note: Lattice Energy also Depends on Crystal Structure There are some other factors to be taken note of like covalent character and electron-electron interactions in ionic solids because the ionic radii of the cations decrease within the order $\,K + {{ }} > {{ }}Na + {{ }} > {{ }}Li + \,$ for a given halide ion, the lattice energy decreases steadily from Lithium to potassium. Conversely, for a given metallic element ion, the fluoride compound always has the highest lattice energy and therefore the iodide salt has very lowest.