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General Chemistry: An Integrated Approach Hill, Petrucci, 4th Edition Chapter 22 The d-Block Elements and Coordination Chemistry Mark P. Heitz State University of New York at Brockport © 2005, Prentice Hall, Inc. On the Periodic Table … d-block elements contain the transition metals EOS Chapter 22: d-Block Elements 2 Relative Orbital Energies in the Fourth-Period Transition Series EOS Chapter 22: d-Block Elements 3 Fourth-Period Properties EOS Chapter 22: d-Block Elements 4 Atomic Radii EOS Chapter 22: d-Block Elements 5 Oxidation Numbers EOS Chapter 22: d-Block Elements 6 Scandium Scandium is rather widely distributed in Earth’s crust, but there is only one mineral from which it is extracted, thortveitite, Sc2Si2O7 Despite its relative rarity, the physical and chemical properties of scandium have been well characterized. Its chemistry is based mostly on the Sc3+ ion Scandium properties resemble main group metals, particularly aluminum EOS Chapter 22: d-Block Elements 7 Titanium Titanium is the ninth most abundant element in Earth’s crust and the second most abundant transition metal (after iron) Three desirable properties make titanium a highly useful metal: (1) low density; (2) high structural strength, even at high temperatures; and (3) corrosion resistance The most important compound of titanium is the oxide, TiO2, and its most important use is as a white pigment in paints, papers, and plastics EOS Chapter 22: d-Block Elements 8 Vanadium Vanadium is reasonably abundant in Earth’s solid crust, ranking nineteenth among the elements It is mostly obtained as a by-product of the production of uranium from carnotite, K2(UO2)2(VO4)2·3 H2O Vanadium is of interest because of (1) its use as an alloying element in steel; (2) the catalytic activity of some of its compounds, principally V2O5; and (3) the range of oxidation number in its ions The different oxidation states of vanadium gives a variety of distinctive colors EOS Chapter 22: d-Block Elements 9 Chromium The most important source of chromium is the mineral chromite, FeCr2O4, or FeO·Cr2O3 In addition to its use in alloys, chromium can be plated onto other metals, generally by electrolysis from a solution containing CrO3 in H2SO4 Dichromate ion, Cr2O72–, is a common oxidizing agent; chromate ion, CrO42–, is a good precipitating agent The name chromium is from chromus (color) because its compounds exhibit many colors Chapter 22: d-Block Elements EOS 10 Manganese Manganese is obtained mainly from the mineral pyrolusite, MnO2 Ferromanganese alloys are wear resistant and shock resistant and are used for railroad tracks, bulldozers, and road scrapers Manganese dioxide is the starting point for making most other manganese compounds Potassium permanganate, KMnO4, is an important oxidizing agent that is used in both analytical and organic chemistry laboratories EOS Chapter 22: d-Block Elements 11 The Iron Triad: Fe, Co, and Ni Iron is the fourth most abundant element in Earth’s crust. Cobalt and nickel are not nearly as common, but they are still sufficiently abundant that their annual production is thousands of tons All three iron triad elements form 2+ ions Ferromagnetism is a much stronger magnetic effect than paramagnetism EOS Chapter 22: d-Block Elements 12 Ferromagnetism and Paramagnetism EOS Chapter 22: d-Block Elements 13 Heme and Hemoglobin Transition metals are required for life … EOS Chapter 22: d-Block Elements 14 Important Metals of Group IB EOS Chapter 22: d-Block Elements 15 Zinc Zinc has many uses, such as in alloys, and is a good electrical conductor Brass is a copper alloy having from 20 to 45% zinc and small quantities of tin, lead, and iron Zinc oxidizes in air to form a thin, adherent oxide coating that protects the underlying metal from further corrosion Because zinc is more easily oxidized than iron, zinc is used in making galvanized iron EOS Chapter 22: d-Block Elements 16 Cadmium Cadmium can substitute for zinc in coating metals for certain applications Its primary uses are in alloys and as electrodes in batteries Because of its capacity to absorb neutrons, cadmium is used in control rods in nuclear reactors Zinc in trace amounts is an essential element for humans; cadmium is quite toxic Its effect may be to substitute for zinc in certain enzymes EOS Chapter 22: d-Block Elements 17 Mercury Mercury differs from zinc and cadmium in at least six significant ways Mercury forms few water-soluble compounds and most of its compounds are not hydrated The physical properties of mercury, especially its metallic and liquid properties and its high density, determine many of its uses Long-term exposure can present a serious health hazard Mercury poisons the body’s systems, in part by interfering with sulfur-containing enzymes Chapter 22: d-Block Elements EOS 18 The Lanthanide Elements The elements cerium through lutetium comprise the first series of the f-block and are called the inner transition elements These elements are frequently called “rare earths,” a name of historical origin but a clear misnomer because several are not rare at all For many uses, the lanthanides do not have to be separated from one another. A mixture of the lanthanide metals with about 25% La is used in certain steel and magnesium-based alloys. Some of the oxides are used to color glass EOS Chapter 22: d-Block Elements 19 Terminology for Complexes A complex consists of a central atom, which is usually a metal atom or ion, and attached groups called ligands The coordination number is the total number of points at which a central atom or ion attaches ligands EOS Chapter 22: d-Block Elements 20 Terminology for Complexes The region surrounding the central atom or ion and containing the ligands is called the coordination sphere A substance consisting of one or more complexes is called a coordination compound EOS Chapter 22: d-Block Elements 21 Cobalt(III) Coordination Cmpds If a complex carries a net electric charge, it is called a complex ion EOS Chapter 22: d-Block Elements 22 Ligands Many metal atoms and ions have empty orbitals that can accommodate electron pairs Ligands with one donor atom have just one point of attachment to the central metal atom or ion and are called monodentate ligands EOS Chapter 22: d-Block Elements 23 Ligands Polydentate refers to multiple points of attachment by one ligand EOS Chapter 22: d-Block Elements 24 Naming Complex Ions In naming a complex, first name the ligands and then the central metal atom or ion as a single compound word Name the ligands in alphabetical order based on the first letters of their names and ignoring prefixes Designate the number of ligands with prefixes Use the unmodified name of the central metal in a complex cation. In a complex anion, add the ending -ate to the name of the central metal Write the names in the order of cation followed by anion Chapter 22: d-Block Elements EOS 25 Some Metals in Complex Anions EOS Chapter 22: d-Block Elements 26 Isomerism in Complex Ions Structural isomers differ in the ligands that are attached to the central atom or in the donor atoms through which the ligands are bonded Geometric isomers differ in the arrangement of the attached ligands, forming either cis- (same side) or trans- (opposite sides) compounds EOS Chapter 22: d-Block Elements 27 Optical Activity Optical isomers are isomers that differ in their ability to rotate the plane of polarized light EOS Chapter 22: d-Block Elements 28 Optical Activity Each of the two molecules or ions of an optical isomer is called an enantiomer and each enantiomer rotates the plane-polarized light in opposite directions EOS Chapter 22: d-Block Elements 29 Crystal Field Theory The attractions between a central atom or ion and its ligands are largely electrostatic To predict the magnetic properties of a complex ion, its structure and the ability of its ligands to split the dorbital energy levels must be known EOS Chapter 22: d-Block Elements 30 d-Level Splitting EOS Chapter 22: d-Block Elements 31 Crystal Field Theory The spectrochemical series shows the relative abilities of some common ligands to split the dorbital energy levels Ligands that produce large energy separations between groups of d orbitals are called “strong field” ligands, and those that produce small separations are “weak field” ligands EOS Chapter 22: d-Block Elements 32 Color in Complex Ions Many complex ions are colored because the energy differences between d orbitals match the energies of components of visible light EOS Chapter 22: d-Block Elements 33 Effect of Ligands on Colors EOS Chapter 22: d-Block Elements 34 Non-visible Transitions Ions having the following electron configurations have no electron transitions in the energy range of visible light noble-gas electron configuration An outer shell with 18 electrons An “18 + 2” configuration (for example, Sn2+) EOS Chapter 22: d-Block Elements 35 Chelates Chelates generally are much more stable than complexes with monodentate ligands The increase in entropy during chelation is an important factor in the stabilities of chelates EDTA (ethylenediaminetetraacetic acid) is commonly used to sequester metal ions in solution Chelation therapy is sometimes used to treat heavy metal ion poisoning EOS Chapter 22: d-Block Elements 36 A Metal–EDTA Complex EOS Chapter 22: d-Block Elements 37 Summary of Concepts • All the elements of the d block are metals • Most metals exist in several oxidation states and form many complex ions and colored compounds • The early members in a period in the d block are active metals but later members are less active • Scandium resembles aluminum but is not widely used • The uses of titanium depend on its high strength, low density, and corrosion resistance • Dichromate and permanganate ions are widely used oxidizing agents EOS Chapter 22: d-Block Elements 38 Summary (cont’d) • Copper, silver, and gold are much less active than earlier members of their periods • Zinc, cadmium, and mercury are not transition elements; their atoms and ions all have filled d subshells • The central metal atom or ion of a metal complex is a Lewis acid; it forms coordinate covalent bonds by accepting lone-pair electrons from ligands, which are Lewis bases • Isomerism among complexes is of two general types: structural and optical EOS Chapter 22: d-Block Elements 39 Summary (cont’d) • Interactions between lone-pair electrons on ligands and electrons in the d orbitals of the central metal atom or ion produce a splitting of the d-orbital energy level • Electron transitions between d orbitals of different energy provide a way for a complex to absorb some wavelength components of visible light and transmit others, giving rise to color • Explanations of the colors and magnetic properties of complexes are facilitated by a special listing of common ligands called the spectrochemical series EOS Chapter 22: d-Block Elements 40