At large interatomic separations, an alkali halide moleculeMX has a lower energy as two neutral atoms, M + X; atshort separations, the ionic form (M+)(X-) has a lowerenergy. At a certain distance, Rc, the energies of the twoforms become equal, and it is near this distance that theelectron will jump from the metal to the halogen atom during a collision. Because the forces between neutral atomsare weak at large distances, a reasonably good approximation can be made by ignoring any variation in potentialV(R) for the neutral atoms between Rc and R - `. For theions in this distance range, V(R) is dominated by theirCoulomb attraction.(a) Express Rc for the first ionization energy of the metalM and the electron affinity of the halogen X.(b) Calculate Rc for LiF, KBr, and NaCl using data fromAppendix F.
At large interatomic separations, an alkali halide molecule
MX has a lower energy as two neutral atoms, M + X; at
short separations, the ionic form (M+)(X-) has a lower
energy. At a certain distance, Rc, the energies of the two
forms become equal, and it is near this distance that the
electron will jump from the metal to the halogen atom during a collision. Because the forces between neutral atoms
are weak at large distances, a reasonably good approximation can be made by ignoring any variation in potential
V(R) for the neutral atoms between Rc and R - `. For the
ions in this distance range, V(R) is dominated by their
Coulomb attraction.
(a) Express Rc for the first ionization energy of the metal
M and the
(b) Calculate Rc for LiF, KBr, and NaCl using data from
Appendix F.
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