# 23.E: Exercises


## 23.4: First-Row Transition Metal Elements: Scandium to Manganese

### Conceptual Problems

1. The valence electron configuration of Sc is 4s23d1, yet it does not lose the d1 electron to form 1+ ion. Why?
2. Give the ground-state electron configuration for Mn, Mn2+, Au, Au3+, Mo, and Mo5+.
3. A great deal of research is being conducted on the use of titanium alloys as materials for transportation applications (airplanes, ships, automobiles, etc.). Why is Ti particularly suited to this purpose? What is the primary disadvantage that needs to be overcome?
4. Both Ti and Ta are used for bioimplants because they are highly resistant to corrosion. Their uses also extend to other applications where corrosion must be avoided. Why are these metals so corrosion resistant?
5. Give two reasons why Zr is used to make the casing for UO2 fuel in water-cooled nuclear reactors.
6. Why is chromium added to steel to form stainless steel? What other elements might also be effective additives for this purpose? Why did you select these elements?
7. Tungsten is commonly used as the filament in electric light bulbs. Why is tungsten particularly suited to this purpose?
8. Palladium metal is used to purify H2 by removing other gases. Why is Pd so permeable to H2?
9. Give the valence electron configuration for Sc, Fe, Re, Ag, Zr, Co, V, Pr, Hg, Cr, Ni, Ce, Cu, and Tb.
10. The Hg–Hg bond is much stronger than the Cd–Cd bond, reversing the trend found among the other transition-metal groups. Explain this anomaly.
11. Which of the transition metals are most likely to form compounds in the +6 oxidation state? Why?

### Structure and Reactivity

1. Do you expect TiCl4, TiCl3, TiCl2, and Ti to be oxidized, reduced, or hydrolyzed by water? Explain your reasoning.
2. The atomic radii of vanadium, niobium, and tantalum are 134 pm, 146 pm, and 146 pm, respectively. Why does the radius increase from vanadium to niobium but not from niobium to tantalum?
3. The most stable oxidation state for the metals of groups 3, 4, and 5 is the highest oxidation state possible. In contrast, for nearly all the metals of groups 8, 9, and 10, intermediate oxidation states are most stable. Why?
4. Most of the transition metals can form compounds in multiple oxidation states. Ru, for example, can form compounds in the +8, +6, +4, +3, +2, and −2 oxidation states. Give the valence electron configuration of Ru in each oxidation state. Why does Ru exhibit so many oxidation states? Which ones are the most stable? Why?
5. Predict the maximum oxidation states of Cu, Cr, Mo, Rh, Zr, Y, Ir, Hg, and Fe.
6. In the +4 oxidation state all three group 7 metals form the dioxides (MO2). Which of the three metals do you expect to form the most stable dioxide? Why?
7. Of [Fe(H2O)6]+, OsBr7, CoF4, PtF6, FeI3, [Ni(H2O)6]2+, OsO4, IrO4, NiO, RhS2, and PtH, which do not exist? Why?
8. The chemistry of gold is somewhat anomalous for a metal. With which elements does it form the Au ion? Does it form a stable sulfide?
9. Of Os4+, Pt10+, Cr6+, Ir9+, Ru8+, Re7+, and Ni10+, which are not likely to exist? Why?
10. Of Ag2S, Cu2S, AuI3, CuF, AuF, AgN, and AuO, which are not likely to exist?
11. There is evidence that the Au ion exists. What would be its electron configuration? The compound CsAu has been isolated; it does not exhibit a metallic luster and does not conduct electricity. Is this compound an alloy? What type of bonding is involved? Explain your answers.
12. Of Hg2Cl2, ZnO, HgF2, Cs2[ZnCl5], and HgNa, which are not likely to exist?
13. Mercurous oxide (Hg2O) and mercurous hydroxide [Hg2(OH)2] have never been prepared. Why not? What products are formed if a solution of aqueous sodium hydroxide is added to an aqueous solution of mercurous nitrate [Hg2(NO3)2]?
14. Arrange Fe2O3, TiO2, V2O5, MoO3, Mn2O7, and OsO4 in order of increasing basicity.
15. Mercurous sulfide has never been prepared. What products are formed when H2S gas is bubbled through an aqueous solution of mercurous nitrate?
16. Arrange Sc2O3, VO, V2O5, Cr2O3, Fe2O3, Fe3O4, and ZnO in order of increasing acidity.
17. Arrange Sc2O3, V2O5, CrO3, Mn2O7, MnO2, and VO2 in order of increasing basicity.
18. Predict the products of each reaction and then balance each chemical equation.
1. Ti + excess Cl2, heated
2. V2O5 in aqueous base
3. K2Cr2O7 + H2SO4
4. RuBr2 + O2, in water
5. [CrO4]2− in aqueous acid
6. Hg2+ + Hg, in aqueous acid
1. Predict the products of each reaction and then balance each chemical equation.
1. AgBr + hν
2. W + excess Cl2, heated
3. CuO + H2, heated
4. Fe2O3 in aqueous acid
5. RhCl3 + NH3, in water
6. Fe2+ + [MnO4], in water
1. What do you predict to be the coordination number of Pt2+, Au+, Fe3+, and Os2+?
2. Of La, Sc, Cr, and Hf, which is most likely to form stable compounds in the +4 oxidation state? Why?
3. Give the most common oxidation state for Y, W, Ru, Ag, Hg, Zn, Cr, Nb, and Ti.
4. Give the most common oxidation state for Os, Cd, Hf, V, Ac, Ni, Mn, Pt, and Fe.
5. Give the highest oxidation state observed for Zr, Fe, Re, Hg, Ni, La, and Mo.
6. Give the highest oxidation state observed for Ag, Co, Os, Au, W, and Mn.
7. Arrange La, Cs, Y, Pt, Cd, Mo, Fe, Co, and Ir in order of increasing first ionization energy.
8. Briefly explain the following trends within the transition metals.
1. Transition-metal fluorides usually have higher oxidation states than their iodides.
2. For a given metal, the lowest-oxidation-state oxide is basic and the highest-oxidation-state oxide is acidic.
3. Halides of the transition metals become more covalent with increasing oxidation state and are more prone to hydrolysis.
1. Propose a method to prepare each of the following compounds: TiCl4[(CH3)2O]2, Na2TiO3, V2O5, and Na2Cr2O7.
2. Of the group 5 elements, which
1. has the greatest tendency to form ions in the lower oxidation states?
2. has the greatest tendency to form a polymeric fluoride?
3. does not form an MX2 species?
4. forms the most basic oxide?
5. has the greatest tendency to form complexes with coordination numbers higher than 6?

1. Pt10+, Ir9+, and Ni10+. Because ionization energies increase from left to right across the d block, by the time you reach group 9, it is impossible to form compounds in the oxidation state that corresponds to loss of all the valence electrons.
1. Hg22+(aq) + H2S(g) → Hg(l) + HgS(s) + 2H+(aq)
1. Mn2O7 < CrO3 < V2O5 < MnO2 ≈ VO2 < Sc2O3
1. 2AgBr(s) $$\xrightarrow{\mathrm{light}}$$ 2Ag(s) + Br2(l)
2. W(s) + excess Cl2(g) $$\xrightarrow{\Delta}$$ WCl6(s)
3. CuO(s) + H2(g) $$\xrightarrow{\Delta}$$ Cu(s) + H2O(g)
4. Fe2O3(s) + 6H+(aq) → 2Fe3+(aq) + 3H2O(l)
5. RhCl3(s) + 6NH3(aq) → [Rh(NH3)6]Cl3(aq)
6. 3Fe2+(aq) + MnO4(aq) + 7H2O(aq) → Fe3+(aq) + MnO2(s) + 5H+(l)
1. Os, +4; Cd, +2; Hf, +4; V, +5; Ac, +3; Ni, +2; Mn, +2; Pt, +2 & +4; Fe, +2 & +3
1. Ag, +3; Co, +4; Os, +8; Au, +5; W, +6; Mn, +7

## 23.5: The Iron Triad: Iron, Cobalt, and Nickel

### Practice Problems

1. Fe2O3(s) + 3CO(g) --> 2Fe (l) + 2CO2(g)

2. 5Fe2+(aq) + MnO4-(aq) + 8H+(aq) --> 5Fe3+(aq) + Mn2+(aq) +4H2O(l)

3. [Fe(H2O)6]3+ +SCN-(aq) --> [FeSCN(H2O)5]2+ + H2O(l)

4. 4FeS + 7O2 --> 2Fe2O3 + 4SO2

5. Ni + H2O --> No Reaction

## 23.8: Lanthanides

### Practice Problems

1. Which elements are considered to be Lanthanides?
2. How do the Lanthanides react with oxygen?
3. What causes the Lanthanide Contraction?
4. Why do Lanthanides exhibit strong electromagnetic and light properties?
5. What do the Lanthanides have in common with the Noble Gases?

1. Elements Lanthanum (57) through Lutetium (71) on the periodic table are considered to be Lanthanides.
2. Lanthanides tend to react with oxygen to form oxides. The reaction at room temperature can be slow while heat can cause the reaction to happen rapidly.
3. The Lanthanide Contraction refers to the decrease in atomic size of the elements in which electrons fill the f-subshell. Since the f sub-shell is not shielded, the atomic size will decrease as the nuclear charge still increases.
4. Lanthanides exhibit strong electromagnetic and light properties because of the presence of unpaired electrons in the f-orbitals. The majority of the Lanthanides are paramagnetic, which means that they have strong magnetic fields.
5. Both the Lanthanides and Noble Gases tend to bind with more electronegative atoms, such as Oxygen or Fluorine.

## 23.9: High Temperature Superconductors

1. Why does the BCS theory predict that superconductivity is not possible at temperatures above approximately 30 K?
2. How does the formation of Cooper pairs lead to superconductivity?

Solution

1. According to BCS theory, the interactions that lead to formation of Cooper pairs of electrons are so weak that they should be disrupted by thermal vibrations of lattice atoms above about 30 K.

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