Magnesium oxide, lattice energy

Calculations of the interaction energy in very fine pores are based on one or other of the standard expressions for the pair-wise interaction between atoms, already dealt with in Chapter 1. Anderson and Horlock, for example, used the Kirkwood-Miiller formulation in their calculations for argon adsorbed in slit-shaped pores of active magnesium oxide. They found that maximum enhancement of potential occurred in a pore of width 4-4 A, where its numerical value was 3-2kcalmol , as compared with 1-12, 1-0 and 1-07 kcal mol for positions over a cation, an anion and the centre of a lattice ceil, respectively, on a freely exposed (100) surface of magnesium oxide. 

Compounds of aluminium and magnesium in the lower oxidation states, A1(I) and Mg (I), do not exist under normal conditions. If we make an assumption that the radius of AF or Mg is the same as that of Na (same row of the Periodic Table), then we can also equate the lattice energies, MCI. Use this information in a Born-Haber cycle to calculate... 

Explain why the lattice energy of magnesium oxide (3850 kj-mol 1) is greater than that of barium oxide (3114 kj-mol 1), given that they have similar arrangements of ions in the crystal lattice. See Appendix 2D. 

If there is so much lattice energy to be gained in going from singly charged to doubly charged ions in the case of magnesium oxide, why then does solid... 

There will be more attraction between 2+ and 2- ions in a lattice and so the values for lattice enthalpy should be more exothermic, resulting in a more stable lattice. For example, compare the lattice energies of the oxides and chlorides of magnesium and sodium ... 

Write the specific chemical reactions whose enthalpy change (or negative thereof) represent the lattice energy of (a) potassium fluoride, KF (b) magnesium selenide, MgSe (c) sodium oxide, NajO (d) sodium peroxide, Na202-... 

We need to construct a thermodynamic cycle involving a metal oxide for which all quantities except the second electron affinity are either known experimentally or, in the case of lattice energy, available from the Bom-Lande or Kapustinskii equation. Such a cycle for magnesium oxide is shown in Figure 8.6. MgO assumes a rock salt structure, and its lattice energy is obtained from the Born-Lande equation as shown... 

In view of the facts that twice as much energy is required to remove the second electron from magnesium as to remove the first and that addition of an electron to the gaseous 0 ion is quite endothermic, it seems puzzling that magnesium oxide contains Mg and 0 ions rather than Mg and O ions. The answer lies in the lattice energy. Note that the... 

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