Sodium fluoride lattice energy, 196

Although the data for the silver halides suggest that silver(I) fluoride is likely to be more soluble than the other silver halides (which is in fact the case), the hydration enthalpies for the sodium halides almost exactly balance the lattice energies. What then is the driving force which makes these salts soluble, and which indeed must be responsible for the solution process where this is endothermic We have seen on p. 66 the relationship AG = — TAS and... 

Sodium fluoride, NaF, is a favorable choice for X-ray analysis of the lattice energy of an ionic crystal. Both Na and F are relatively light atoms, and the Na 3s-radial distribution, though diffuse, is not quite as spread out as the Li 2s shell (single-C values are 0.8358 and 0.6396 au-1, respectively see appendix F), and therefore contributes to a larger number of reflections. 

The electrostatic contribution to the lattice energy, L, for the sodium fluoride arrangement (the energy required to form gas phase ions from the solid crystalline lattice) is the value of the change in internal energy (i.e. A U) for the reaction ... 

Properties of the alkali fluorides.—The anhydrous alkali fluorides crystallize in the cubic system.8 Lithium fluoride forms regular optohedrons and nacreous plates sodium fluoride crystallizes in cubes, but in presence of sodium carbonate, the crystals are octohedrons. The cubic crystals are frequently en tremies. H. Schwendenwein has discussed the space lattice of the alkali fluorides, and K. Fajans and H. Grimm estimated the distance of the atoms apart in sodium and potassium fluorides to be respectively 2 34 X 10 8 and 2 67 X10-8 cm. and the respective lattice energies to be 210-4 and 192 2 Cals, per mol. The taste of potassium fluoride is acrid and salty. 

Sodium fluoride and sodium chloride both crystallize into the same type of structure. Which do you predict to have the higher lattice energy, NaF or NaCl ... 

The lattice energy of an ionic crystal may be defined as the energy emitted when the correct number of ions emerge from distant locations and station themselves in their appropriate places in the crystal lattice. For a mole of sodium fluoride, for example, one may obtain such a lattice energy by multiplying the potential energy (as given in Equation... 

Sodium fluoride adopts the NaCl structure type. Estimate the lattice energy of NaF using an electrostatic model. 

Use the concept of lattice energy to rationahze why sodium fluoride dissolves in water, whereas calcium fluoride does not. Extending this reasoning, would you e q>ect magnesium fluoride to be soluble ... 

Hence, if one brings together a good electron donor (such as a sodium atom) and a good electron acceptor (such as a fluorine atom), one might expect a chemical reaction to occur. Electrons are transferred and an ionic compound (sodium fluoride, NaF) is produced. A three-dimensional solid lattice of sodium and fluoride ions is created, where each sodium ion is surrounded by fluoride ions, and each fluoride ion is in turn surrounded by sodium ions. Another very important aspect of such a relation is the fact that energy is released as the product is formed. This release of energy associated with the formation of the reaction products becomes very important in the consideration of the chemistry of pyrotechnics and explosives. 

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-... 

Determine the enthalpy change of solution of sodium fluoride using the following data lattice energy=-902 kJ mob enthalpy change of hydration of sodium ions =-406 kJmob ... 

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