GEOL237 Principles of Chemical Geology
Exercise #1
ภาคเรียนที่ 1 ปี การศึกษา 2554
กำหนดส่ง: 20 มิถุนายน 2554
(1) Refer to the figure below on first ionization potential (IE).
(1.1) Why is the first ionization potential of nitrogen greater than that of either carbon or
oxygen?
(1.2) Why do the first ionization potentials decrease from helium (He) to krypton (Kr)?
(2) Given that the order of fill for electron orbitals is 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, … For the
element with atomic number (Z) of 24, which one(s) of the following electron
configurations seems reasonable? For each configuration, state why you “accepted” or
“rejected” it?
(a) 1s2, …, 4s2, 3d4
(b) 1s2, …, 4s1, 3d5
(c) 1s2, …, 4s0, 3d6
(3) Refer to Table 4.5 (p. 181-182) in KH-chap4.pdf (electronic configurations of the elements)
to answer the following questions about the elements with atomic numbers (Z) 53, 54, and
55.
(3.1) Which one has the highest electronegativity? Why?
(3.2) Which one has the highest ionization potential? Why?
(4) Consider the “general” element/atom “Q”. Is the ionic radius of Q- the same under all
conditions? Why or Why not?
(5) Why is the radius of Fe3+ smaller than the radius of Fe2+?
(6) Given the radii of calcium (Ca2+), cadmium (Cd2+), oxygen (O2-), and sulfur (S2-) of 1.0, 0.95,
1.40, and 1.84 Å, respectively. If the bond lengths (or inter-ionic distance) of the
compounds CaO, CdO, CaS, and CdS are given in the following table, use these data to
answer the following questions.
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Solids
CaO
CdO
CaS
CdS
Inter-ionic Distance
(Å)
2.40
2.34
2.80
2.51
(6.1) Calculate radius ratio for all four compounds and predict coordination number (CN)
for cations. Then, calculate ionic character (IC or %Ionic) based on their differences in
electronegativity (E) using the following formula:
%IC  100 1  e0.25 E 


2
Bond
Radius Ratio (R+/R-)
Predicted CN
for cations
(L. Pauling,1960)
Ionic Character
(%)
Ca2+O2Cd2+O2Ca2+S2Cd2+S2(6.2) Explain why the bond length (or inter-ionic distance) between Cd2+ and S2- in cadmium
sulfide is smaller than the sum of radii of the two?
(6.3) Which compound is more ionic and which compound is more covalent?
(6.4) Does the compound that is more covalent have shorter bond length? Why?
(7) From the following ionic structure of calcium fluoride and cesium chloride shown next
page, do the ‘electrostatic valency’ principle for Ca2+, F-, Cl-, and Cs+ ions.
Figure 1: Calcium fluoride (fluorite, CaF2) and cesium chloride (CsCl) structures.
(8) If an ion A+ in an “ionic” compound A2X has coordination number (CN) of 4, what should
the coordination number of X be? [Use electrostatic valency principle]
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(9) Why does the zinc ion (Zn2+), in many of its compounds, show tetrahedral coordination (CN
= 4) although its ionic radius is similar to that of ions like Mg2+ which show only octahedral
coordination (CN = 8)?
(10) In each of the following pairs, choose one in which the chemical bond would have more
covalent character and explain why?:
(10.1)
KCl and KI
(10.2)
KCl and BaCl2
(10.3)
Li2S and Cs2S
(10.4)
Cu2O and Cu2S
(10.5)
BaCl2 and HgCl2
(10.6)
B2O3 and Al2O3
(11) In p.110 of KB-chap5.pdf, there is an example calculation of the average sizes of Na+ and
Cl- in sodium chloride. Use the same method to determine the average size of Cs+ and Cl- if
CsCl has a density of 2.31 g/cm3. Assume the sizes of Cs+ and Cl- ions are equal.
(12) Arrange the following elements in terms of (a) increasing ionization energy and (b)
increasing atomic radius: O, Se, C, Si, F.
(13) By examining the distances between ions in a salt it is possible to define ionic radii in a
manner similar to the way that atomic radii were defined. Listed below are the atomic and
ionic (+2) radii for calcium and zinc:
Radii (Å)
Ca
Zn
1.97
1.34
Ca2+
Zn2+
1.00
0.74
(13.1)
Explain why the atomic radius of calcium is larger than that of zinc?
(13.2)
Suggest a reason why the difference in the ionic radii is much less than the
difference in the atomic radii.
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