2003.11.12
1.Among the thirteen possible monoclinic space groups are P2 , P2 /m, and
1 1
P2 /c. Compare these space groups by listing the symmetry elements for
1
each. (9%)
2.Both CsCl and CaF2 exhibit a coordination number of 8 for the cations.
What is the structural relationship between these two lattices? (10%)
3.Show your understanding of the meaning of the Madelung constant by
calculating A for the isolated F-Be2+F- fragment considered as a purely
ionic species. (5%)
4.To ionize Mg to Mg2+ costs two times as much energy as to form Mg+. The
formation of O2- is endothermic rather than exothermic as O-. Nevertheless
, magnesium oxide is always formulated as Mg2+O2- rather than Mg+O-.
a.What theoretical reason can be given for the Mg2+O2- formulation?
b.What simple experiment could be performed to prove that magnesium oxide
was not Mg+O-? (6%)
5.The crystal structure of LaF3 is different from those discussed. Assume it
is unknown. Using the equation of Kapustinskii, estimate the lattice
energy. (rLa3+ = 117.2pm ; rF- = 119pm) (10%)
6.Which of the following will exhibit the greater polarizing power? Give the
reason for your answer. (10%)
a.K+ or Ag+ b.K+ or Li+ c.Li+ or Be2+ d.Cu2+ or Ca2+ e.Ti2+ or Ti4+
7.Derive the following of Born-Land'e equation for the lattice energy of an
ionic compound: ANZ+Z-E^2 1
U0 = ─────(1 - ─)
4πε0r0 n (10%)
8.Draw the following crystal structure and describe the arrangement of the
cations and anions for the following species.
a.ZnS(wurtzite) b.ZnS(zinc blende) c.CaF2(fluorite) d.Li2O(anitfluorite)
e.TiO2(rutile) (25%)
9.Draw a diagram to describe the energy changes involved in the formation of
solid NaF from its element and calculate the electron affinity of the F
atom with the following quantities (in KJ/mol):
Lattice energy of NaF:-923;
Dissociation energy of F2(g):154
Heat of sublimation of Na metal:109
Ionization energy of the Na atom:495
Heat of formation of solid NaF:-570 (10%)
10.Write down the International notations (Hermann-Mauguin system) for the
following corresponding Schoenflies notations:
a.C2v b.C2h c.C3v d.D3d e.C6h (5%)
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