Cohesive Energies of Ionic Solids

• C. N. R. Rao

Abstract

The cohesive energy of an ionic solid is the energy required to separate a gram molecule of ions at equilibrium distances in a solid to infinite distances apart. This energy can be evaluated from thermochemical data employing the Born-Haber Cycle. Let us consider the series of reactions that would give the heat of formation of an ionic solid MX
$${M_{solid}} + {S_M} \to {M_{vapor}}$$
(1)
$${M_{vapor}} + {I_M} \to {M^ + } + e$$
(2)
$$\frac{1} {2}{X_2} + \frac{1} {2}{D_{{x_2}}} \to X$$
(3)
$$X + e \to {X^ - } + E_x^A$$
(4)
$$({M^ + } + {M^ - })gas \to + M{X_{solid}} + {U_L}$$
(5)
$${M_{solid}} + \frac{1} {2}{X_2} + {X_2} + {S_M} + {I_M} + \frac{1} {2}{D_{{x_2}}} \to M{X_{solid}} + E_x^A + {U_L}$$
(6)
Further,
$${M_{solid}} + \frac{1} {2}{X_2} \to M{X_{solid}} + \Delta {H_f}$$
(7)
If the heat of sublimation SM, the ionization potential IM, the $${D_{{x_2}}}$$ dissociation energy Dx2, electron affinity (Math) and the heat of formation ΔHf are known experimentally, the cohesive energy, UL, per an ion pair of MX can be calculated
$$- {U_L} = {S_M} + {I_M} + \frac{1} {2}{D_{{x_2}}} - E_x^A - \Delta {H_f}$$
(8)
Note that all the energy quantities in 1 to 7 are per atom or molecule. The experimental values of the energy quantities for a few ionic solids are listed in Table 1.

Keywords

Cohesive Energy Lattice Energy Ionic Crystal Alkali Halide Energy Quantity
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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