How is lattice energy calculated?
Lattice energy of ionic crystals is calculated using the concept of coulombic interactions between all its ions. This is directly proportional to the product of charges of cations and anions, and inversely proportional to the distance between two oppositely charged ions. Thus, the energy of the lattice is the sum of all such interacting oppositely charged ions. Lattice energy = potential enegy of attraction + potential energy of repulsion. It is believed that when two oppositely charged ions approach each other, an attractive force act between them. This force may turn into repulsion, because the electron cloud, when come in closer proximity as the ions come nearer, repel each other and this force predominates over the force of attraction due to opposite charges on the ions. Thus, Thus lattice energy = – [{(z+)(z-)e²}/r] + [{(b)(e²)}/(r^n)]. Where, n is “Born exponent” and b is “Repulsion co-efficient”. e = charge on an electron and r = distance between two ions. z = unit charge on an