Private: Chapter Nineteen
Key Terms, Key Equations, Summaries, and Exercises (Chapter 19)
Key Terms
actinide series (also, actinoid series) actinium and the elements in the second row or the f-block, atomic numbers 89–103
bidentate ligand ligand that coordinates to one central metal through coordinate bonds from two different atoms
central metal ion or atom to which one or more ligands is attached through coordinate covalent bonds
chelate complex formed from a polydentate ligand attached to a central metal
chelating ligand ligand that attaches to a central metal ion by bonds from two or more donor atoms
cis configuration configuration of a geometrical isomer in which two similar groups are on the same side of an imaginary reference line on the molecule
coordination compound stable compound in which the central metal atom or ion acts as a Lewis acid and accepts
one or more pairs of electrons
coordination compound substance consisting of atoms, molecules, or ions attached to a central atom through
Lewis acid-base interactions
coordination number number of coordinate covalent bonds to the central metal atom in a complex or the number of closest contacts to an atom in a crystalline form
coordination sphere central metal atom or ion plus the attached ligands of a complex
crystal field splitting (Δoct) difference in energy between the t2g and eg sets or t and e sets of orbitals
crystal field theory model that explains the energies of the orbitals in transition metals in terms of electrostatic interactions with the ligands but does not include metal ligand bonding
d-block element one of the elements in groups 3–11 with valence electrons in d orbitals
donor atom atom in a ligand with a lone pair of electrons that forms a coordinate covalent bond to a central metal
eg orbitals set of two d orbitals that are oriented on the Cartesian axes for coordination complexes; in octahedral complexes, they are higher in energy than the t2g orbitals
f-block element (also, inner transition element) one of the elements with atomic numbers 58–71 or 90–103 that have valence electrons in f orbitals; they are frequently shown offset below the periodic table
first transition series transition elements in the fourth period of the periodic table (first row of the d-block), atomic numbers 21–29
fourth transition series transition elements in the seventh period of the periodic table (fourth row of the d-block), atomic numbers 89 and 104–111
geometric isomers isomers that differ in the way in which atoms are oriented in space relative to each other, leading to different physical and chemical properties
high-spin complex complex in which the electrons maximize the total electron spin by singly populating all of the orbitals before pairing two electrons into the lower-energy orbitals
hydrometallurgy process in which a metal is separated from a mixture by first converting it into soluble ions, extracting the ions, and then reducing the ions to precipitate the pure metal
ionization isomer (or coordination isomer) isomer in which an anionic ligand is replaced by the counter ion in the inner coordination sphere
lanthanide series (also, lanthanoid series) lanthanum and the elements in the first row or the f-block, atomic numbers 57–71
ligand ion or neutral molecule attached to the central metal ion in a coordination compound
linkage isomer coordination compound that possesses a ligand that can bind to the transition metal in two different ways (CN− vs. NC−)
low-spin complex complex in which the electrons minimize the total electron spin by pairing in the lower-energy orbitals before populating the higher-energy orbitals
monodentate ligand that attaches to a central metal through just one coordinate covalent bond
optical isomer (also, enantiomer) molecule that is a nonsuperimposable mirror image with identical chemical and physical properties, except when it reacts with other optical isomers
pairing energy (P) energy required to place two electrons with opposite spins into a single orbital
platinum metals group of six transition metals consisting of ruthenium, osmium, rhodium, iridium, palladium, and platinum that tend to occur in the same minerals and demonstrate similar chemical properties
polydentate ligand ligand that is attached to a central metal ion by bonds from two or more donor atoms, named with prefixes specifying how many donors are present (e.g., hexadentate = six coordinate bonds formed)
rare earth element collection of 17 elements including the lanthanides, scandium, and yttrium that often occur together and have similar chemical properties, making separation difficult
second transition series transition elements in the fifth period of the periodic table (second row of the d-block), atomic numbers 39–47
smelting process of extracting a pure metal from a molten ore
spectrochemical series ranking of ligands according to the magnitude of the crystal field splitting they induce
steel material made from iron by removing impurities in the iron and adding substances that produce alloys with properties suitable for specific uses
strong-field ligand ligand that causes larger crystal field splittings
superconductor material that conducts electricity with no resistance
t2g orbitals set of three d orbitals aligned between the Cartesian axes for coordination complexes; in octahedral complexes, they are lowered in energy compared to the eg orbitals according to CFT
third transition series transition elements in the sixth period of the periodic table (third row of the d-block), atomic numbers 57 and 72–79
trans configuration configuration of a geometrical isomer in which two similar groups are on opposite sides of an imaginary reference line on the molecule
weak-field ligand ligand that causes small crystal field splittings
Summary
19.1 Occurrence, Preparation, and Properties of Transition Metals and Their Compounds
The transition metals are elements with partially filled d orbitals, located in the d-block of the periodic table. The reactivity of the transition elements varies widely from very active metals such as scandium and iron to almost inert elements, such as the platinum metals. The type of chemistry used in the isolation of the elements from their ores depends upon the concentration of the element in its ore and the difficulty of reducing ions of the elements to the metals. Metals that are more active are more difficult to reduce.
Transition metals exhibit chemical behavior typical of metals. For example, they oxidize in air upon heating and react with elemental halogens to form halides. Those elements that lie above hydrogen in the activity series react with acids, producing salts and hydrogen gas. Oxides, hydroxides, and carbonates of transition metal compounds in low oxidation states are basic. Halides and other salts are generally stable in water, although oxygen must be excluded in some cases. Most transition metals form a variety of stable oxidation states, allowing them to demonstrate a wide range of chemical reactivity.
19.2 Coordination Chemistry of Transition Metals
The transition elements and main group elements can form coordination compounds, or complexes, in which a central metal atom or ion is bonded to one or more ligands by coordinate covalent bonds. Ligands with more than one donor atom are called polydentate ligands and form chelates. The common geometries found in complexes are tetrahedral and square planar (both with a coordination number of four) and octahedral (with a coordination number of six). Cis and trans configurations are possible in some octahedral and square planar complexes. In addition to these geometrical isomers, optical isomers (molecules or ions that are mirror images but not superimposable) are possible in certain octahedral complexes. Coordination complexes have a wide variety of uses including oxygen transport in blood, water purification, and pharmaceutical use.
19.3 Spectroscopic and Magnetic Properties of Coordination Compounds
Crystal field theory treats interactions between the electrons on the metal and the ligands as a simple electrostatic effect. The presence of the ligands near the metal ion changes the energies of the metal d orbitals relative to their energies in the free ion. Both the color and the magnetic properties of a complex can be attributed to this crystal field splitting. The magnitude of the splitting (Δoct) depends on the nature of the ligands bonded to the metal. Strong-field ligands produce large splitting and favor low-spin complexes, in which the t2g orbitals are completely filled before any electrons occupy the eg orbitals. Weak-field ligands favor formation of high-spin complexes. The t2g and the eg orbitals are singly occupied before any are doubly occupied.
19.1 Occurrence, Preparation, and Properties of Transition Metals and Their Compounds
1.
Write the electron configurations for each of the following elements:
(a) Sc
(b) Ti
(c) Cr
(d) Fe
(e) Ru
2.
Write the electron configurations for each of the following elements and its ions:
(a) Ti
(b) Ti2+
(c) Ti3+
(d) Ti4+
3.
Write the electron configurations for each of the following elements and its 3+ ions:
(a) La
(b) Sm
(c) Lu
4.
Why are the lanthanoid elements not found in nature in their elemental forms?
5.
Which of the following elements is most likely to be used to prepare La by the reduction of La2O3: Al, C, or Fe? Why?
6.
Which of the following is the strongest oxidizing agent: VO43,
CrO42−,
or MnO4−?
7.
Which of the following elements is most likely to form an oxide with the formula MO3: Zr, Nb, or Mo?
8.
The following reactions all occur in a blast furnace. Which of these are redox reactions?
(a) 3Fe2O3(𝑠)+CO(𝑔)⟶2Fe3O4(𝑠)+CO2(𝑔)
(b) Fe3O4(𝑠)+CO(𝑔)⟶3FeO(𝑠)+CO2(𝑔)
(c) FeO(𝑠)+CO(𝑔)⟶Fe(𝑙)+CO2(𝑔)
(d) C(𝑠)+O2(𝑔)⟶CO2(𝑔)
(e) C(𝑠)+CO2(𝑔)⟶2CO(𝑔)
(f) CaCO3(𝑠)⟶CaO(𝑠)+CO2(𝑔)
(g) CaO(𝑠)+SiO2(𝑠)⟶CaSiO3(𝑙)
9.
Why is the formation of slag useful during the smelting of iron?
10.
Would you expect an aqueous manganese(VII) oxide solution to have a pH greater or less than 7.0? Justify your answer.
11.
Iron(II) can be oxidized to iron(III) by dichromate ion, which is reduced to chromium(III) in acid solution. A 2.5000-g sample of iron ore is dissolved and the iron converted into iron(II). Exactly 19.17 mL of 0.0100 M Na2Cr2O7 is required in the titration. What percentage of the ore sample was iron?
12.
How many cubic feet of air at a pressure of 760 torr and 0 °C is required per ton of Fe2O3 to convert that Fe2O3 into iron in a blast furnace? For this exercise, assume air is 19% oxygen by volume.
13.
Find the potentials of the following electrochemical cell:
Cd | Cd2+, M = 0.10 ‖ Ni2+, M = 0.50 | Ni
14.
A 2.5624-g sample of a pure solid alkali metal chloride is dissolved in water and treated with excess silver nitrate. The resulting precipitate, filtered and dried, weighs 3.03707 g. What was the percent by mass of chloride ion in the original compound? What is the identity of the salt?
15.
The standard reduction potential for the reaction [Co(H2O)6]3+(𝑎𝑞)+e−⟶[Co(H2O)6]2+(𝑎𝑞)
is about 1.8 V. The reduction potential for the reaction [Co(NH3)6]3+(𝑎𝑞)+e−⟶[Co(NH3)6]2+(𝑎𝑞)
is +0.1 V. Calculate the cell potentials to show whether the complex ions, [Co(H2O)6]2+ and/or [Co(NH3)6]2+, can be oxidized to the corresponding cobalt(III) complex by oxygen.
16.
Predict the products of each of the following reactions. (Note: In addition to using the information in this chapter, also use the knowledge you have accumulated at this stage of your study, including information on the prediction of reaction products.)
(a) MnCO3(𝑠)+HI(𝑎𝑞)⟶
(b) CoO(𝑠)+O2(𝑔)⟶
(c) La(𝑠)+O2(𝑔)⟶
(d) V(𝑠)+VCl4(𝑠)⟶
(e) Co(𝑠)+𝑥𝑠F2(𝑔)⟶
(f) CrO3(𝑠)+CsOH(𝑎𝑞)⟶
17.
Predict the products of each of the following reactions. (Note: In addition to using the information in this chapter, also use the knowledge you have accumulated at this stage of your study, including information on the prediction of reaction products.)
(a) Fe(𝑠)+H2SO4(𝑎𝑞)⟶
(b) FeCl3(𝑎𝑞)+NaOH(𝑎𝑞)⟶
(c) Mn(OH)2(𝑠)+HBr(𝑎𝑞)⟶
(d) Cr(𝑠)+O2(𝑔)⟶
(e) Mn2O3(𝑠)+HCl(𝑎𝑞)⟶
(f) Ti(𝑠)+𝑥𝑠F2(𝑔)⟶
18.
Describe the electrolytic process for refining copper.
19.
Predict the products of the following reactions and balance the equations.
(a) Zn is added to a solution of Cr2(SO4)3 in acid.
(b) FeCl2 is added to a solution containing an excess of Cr2O72−
in hydrochloric acid.
(c) Cr2+ is added to Cr2O72−
in acid solution.
(d) Mn is heated with CrO3.
(e) CrO is added to 2HNO3 in water.
(f) FeCl3 is added to an aqueous solution of NaOH.
20.
What is the gas produced when iron(II) sulfide is treated with a nonoxidizing acid?
21.
Predict the products of each of the following reactions and then balance the chemical equations.
(a) Fe is heated in an atmosphere of steam.
(b) NaOH is added to a solution of Fe(NO3)3.
(c) FeSO4 is added to an acidic solution of KMnO4.
(d) Fe is added to a dilute solution of H2SO4.
(e) A solution of Fe(NO3)2 and HNO3 is allowed to stand in air.
(f) FeCO3 is added to a solution of HClO4.
(g) Fe is heated in air.
22.
Balance the following equations by oxidation-reduction methods; note that three elements change oxidation state.
Co(NO3)2(𝑠)⟶Co2O3(𝑠)+NO2(𝑔)+O2(𝑔)
23.
Dilute sodium cyanide solution is slowly dripped into a slowly stirred silver nitrate solution. A white precipitate forms temporarily but dissolves as the addition of sodium cyanide continues. Use chemical equations to explain this observation. Silver cyanide is similar to silver chloride in its solubility.
24.
Predict which will be more stable, [CrO4]2− or [WO4]2−, and explain.
25.
Give the oxidation state of the metal for each of the following oxides of the first transition series. (Hint: Oxides of formula M3O4 are examples of mixed valence compounds in which the metal ion is present in more than one oxidation state. It is possible to write these compound formulas in the equivalent format MO·M2O3, to permit estimation of the metal’s two oxidation states.)
(a) Sc2O3
(b) TiO2
(c) V2O5
(d) CrO3
(e) MnO2
(f) Fe3O4
(g) Co3O4
(h) NiO
(i) Cu2O
19.2 Coordination Chemistry of Transition Metals
26.
Indicate the coordination number for the central metal atom in each of the following coordination compounds:
(a) [Pt(H2O)2Br2]
(b) [Pt(NH3)(py)(Cl)(Br)] (py = pyridine, C5H5N)
(c) [Zn(NH3)2Cl2]
(d) [Zn(NH3)(py)(Cl)(Br)]
(e) [Ni(H2O)4Cl2]
(f) [Fe(en)2(CN)2]+ (en = ethylenediamine, C2H8N2)
27.
Give the coordination numbers and write the formulas for each of the following, including all isomers where appropriate:
(a) tetrahydroxozincate(II) ion (tetrahedral)
(b) hexacyanopalladate(IV) ion
(c) dichloroaurate(I) ion (note that aurum is Latin for “gold”)
(d) diamminedichloroplatinum(II)
(e) potassium diamminetetrachlorochromate(III)
(f) hexaamminecobalt(III) hexacyanochromate(III)
(g) dibromobis(ethylenediamine) cobalt(III) nitrate
28.
Give the coordination number for each metal ion in the following compounds:
(a) [Co(CO3)3]3− (note that CO32− is bidentate in this complex)
(b) [Cu(NH3)4]2+
(c) [Co(NH3)4Br2]2(SO4)3
(d) [Pt(NH3)4][PtCl4]
(e) [Cr(en)3](NO3)3
(f) [Pd(NH3)2Br2] (square planar)
(g) K3[Cu(Cl)5]
(h) [Zn(NH3)2Cl2]
29.
Sketch the structures of the following complexes. Indicate any cis, trans, and optical isomers.
(a) [Pt(H2O)2Br2] (square planar)
(b) [Pt(NH3)(py)(Cl)(Br)] (square planar, py = pyridine, C5H5N)
(c) [Zn(NH3)3Cl]+ (tetrahedral)
(d) [Pt(NH3)3Cl]+ (square planar)
(e) [Ni(H2O)4Cl2]
(f) [Co(C2O4)2Cl2]3− (note that C2O42−
is the bidentate oxalate ion, −O2CCO2−)
30.
Draw diagrams for any cis, trans, and optical isomers that could exist for the following (en is ethylenediamine):
(a) [Co(en)2(NO2)Cl]+
(b) [Co(en)2Cl2]+
(c) [Pt(NH3)2Cl4]
(d) [Cr(en)3]3+
(e) [Pt(NH3)2Cl2]
31.
Name each of the compounds or ions given in Exercise 19.28, including the oxidation state of the metal.
32.
Name each of the compounds or ions given in Exercise 19.30.
33.
Specify whether the following complexes have isomers.
(a) tetrahedral [Ni(CO)2(Cl)2]
(b) trigonal bipyramidal [Mn(CO)4NO]
(c) [Pt(en)2Cl2]Cl2
34.
Predict whether the carbonate ligand CO32−
will coordinate to a metal center as a monodentate, bidentate, or tridentate ligand.
35.
Draw the geometric, linkage, and ionization isomers for [CoCl5CN][CN].
19.3 Spectroscopic and Magnetic Properties of Coordination Compounds
36.
Determine the number of unpaired electrons expected for [Fe(NO2)6]3−and for [FeF6]3− in terms of crystal field theory.
37.
Draw the crystal field diagrams for [Fe(NO2)6]4− and [FeF6]3−. State whether each complex is high spin or low spin, paramagnetic or diamagnetic, and compare Δoct to P for each complex.
38.
Give the oxidation state of the metal, number of d electrons, and the number of unpaired electrons predicted for [Co(NH3)6]Cl3.
39.
The solid anhydrous solid CoCl2 is blue in color. Because it readily absorbs water from the air, it is used as a humidity indicator to monitor if equipment (such as a cell phone) has been exposed to excessive levels of moisture. Predict what product is formed by this reaction, and how many unpaired electrons this complex will have.
40.
Is it possible for a complex of a metal in the transition series to have six unpaired electrons? Explain.
41.
How many unpaired electrons are present in each of the following?
(a) [CoF6]3− (high spin)
(b) [Mn(CN)6]3− (low spin)
(c) [Mn(CN)6]4− (low spin)
(d) [MnCl6]4− (high spin)
(e) [RhCl6]3− (low spin)
42.
Explain how the diphosphate ion, [O3P−O−PO3]4−, can function as a water softener that prevents the precipitation of Fe2+ as an insoluble iron salt.
43.
For complexes of the same metal ion with no change in oxidation number, the stability increases as the number of electrons in the t2g orbitals increases. Which complex in each of the following pairs of complexes is more stable?
(a) [Fe(H2O)6]2+ or [Fe(CN)6]4−
(b) [Co(NH3)6]3+ or [CoF6]3−
(c) [Mn(CN)6]4− or [MnCl6]4−
44.
Trimethylphosphine, P(CH3)3, can act as a ligand by donating the lone pair of electrons on the phosphorus atom. If trimethylphosphine is added to a solution of nickel(II) chloride in acetone, a blue compound that has a molecular mass of approximately 270 g and contains 21.5% Ni, 26.0% Cl, and 52.5% P(CH3)3 can be isolated. This blue compound does not have any isomeric forms. What are the geometry and molecular formula of the blue compound?
45.
Would you expect the complex [Co(en)3]Cl3 to have any unpaired electrons? Any isomers?
46.
Would you expect the Mg3[Cr(CN)6]2 to be diamagnetic or paramagnetic? Explain your reasoning.
47.
Would you expect salts of the gold(I) ion, Au+, to be colored? Explain.
48.
[CuCl4]2− is green. [Cu(H2O)6]2+is blue. Which absorbs higher-energy photons? Which is predicted to have a larger crystal field splitting?