Properties of the Transition Metals

In addition to the ability of transition metals to adopt a variety of oxidation states, they have the ability to form coordination compounds. Coordination compounds contain complex ions. The ability to form a complex ion is not restricted to transition metals however, most examples you will see involve a transition metal. 

When a transition metal forms a cation it is the s-electrons that leave first. Thus, iron is [Ar]4s23d6, and Fe2+ is [Ar]3d6, and Fe3+ is [Ar]3ds. 

Like their atomic and physical properties, the chemical properties of the transition elements are very different from those of the main-group elements. Let s examine the key properties in the Period 4 transition series. 

Metallic Behavior and Reducing Strength Atomic size and oxidation state have a major effect on the nature of bonding in transition metal compounds. Like the metals in Groups 3A(13), 4A(14), and 5A(15), the transition elements in their lower oxidation states behave chemically more like metals. That is, ionic bonding is more prevalent for the lower oxidation states, and covalent bonding is more 

CHAPTER 22 The Transition Elements and Their Coordination Compounds 

Oxidation States and d-Orbital Occupancy of the Period 4 Transition Metals  

Although the transition metals are less electropositive (or more electronegative) than the alkali and alkaline earth metals, their standard reduction potentials suggest that all of them except copper should react with strong acids such as hydrochloric acid to produce hydrogen gas. However, most transition metals are inert toward acids or react slowly with them because of a protective layer of oxide. A case in point is chromium Despite a rather negative standard reduction potential, it is quite inert 

TABLE 22.1 Electron Configurations and Other Properties of the First-Row Transition Metals  

The electron configurations of the first-row transition metals were discussed in Section 7.9. Calcium has the electron configuration [Ar]4i. From scandium across to copper, electrons are added to the hd orbitals. Thus, the outer electron configuration of scandium is that of titanium is and so on. The two exceptions are 

When the first-row transition metals form cations, electrons are removed first from the 4x orbitals and then from the 3d orbitals. (This is the opposite of the order in which orbitals are filled in atoms.) For example, the outer electron configuration of Fe + is 3d not 4 3d  

Locate the transition metal atoms and ions in the periodic table shown here. Atoms (1) [KrlSs dd. (2) [Xt]6s Af 5d. Ions (3) [Ar]3d (a +4 ion). 

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A systematic correlation of the properties of the/-transition metal ions. S. P. Shina, Struct. Bonding (Berlin), 1976, 30, 1-64 (98). 

Manninen, S., Honkimaki, V., Hamalainen, K., Laukkanen, J., Blaas. C., Redinger, J., McCarthy, J. and Suortti, P. (1996) Compton-scattering study of the electronic properties of the transition-metal alloys FeAI, CoAI, and NiAl, Phys. Rev., B53,7714-7720. 

A guide to the manner in which structural theory may be applied to a detailed consideration of the mechanism of a surface-catalyzed reaction is found in papers by Cossee (113), Arlman (114), and Arlman and Cossee (115) concerning the mechanism of the stereoregular heterogeneous catalyzed polymerization of propylene. Particular crystallographic sites are shown to be the active centers at which the reactants combine and ligand field theory is used to demonstrate a plausible relationship between the activation energy for the conversion of adsorbed reactants to the product and the properties of the transition metal complex which constitutes the reaction center. 

In the following chapter some special magnetic properties of the transition metal fluorides will be dealt with, which depend more clearly upon a specific bonding behaviour in and between the MeFe-octahedra than the crystal structure itself. 

The H-abstraction reaction, however, does not determine selectivity entirely. Depending on the experimental conditions, as discussed earlier, butadiene desorption could be one important step. In this case, the electronic properties of the transition metal ions that determine the interaction with the unsaturated hydrocarbon have to be considered. 

Both the controversy initiated through these early investigations, and the fundamentally interesting properties of the transition metal carbides and nitrides, have stimulated tremendous interest in providing a model for the bonding in these materials. As electronic structure calculations have become more common as a tool in the study of solid state properties, numerous models have been proposed.12 19... 

Much interest has been generated in various properties of metal derivatives of dithioketones, ethylene (1, 2) dithiolates, and related compounds in recent years (17,18,29, 43, 65, 66). There are many interesting facets of these fascinating compounds, and the previously mentioned references cover them in some detail. We limit ourselves here to the structures of the Pt group metals of these engrossing ligands. Unfortunately, some of the more interesting properties of the transition metals... 

Terry M. Tritt and R. T. Littleton, IV, Thermoelectric Properties of the Transition Metal Pentatellurides Potential Low-Temperature Thermoelectric Materials Franz Freibert, Timothy W. Darling, Albert Miglori, and Stuart A. Trugman, Thermomagnetic Effects and Measurements... 

Ferric chloride solutions react very slowly with NF3 at 100° C. the FeCl3 acts as a hydrolysis catalyst, yielding nitric oxide and nitrate. This catalysis is not a general property of the transition metal ions as shown by the total inertness of NF3 to solutions of CoCl2, MnSC>4, CuS04, and NiS04 at 100° C. over periods up to 7 days. 

In all of these compounds, even the tetrahedral ones, a possible starting point for the calculation of properties is an ionic electronic structure with the effects of interatomic matrix elements treated in perturbation theory. As wc liave indiettted, and as will be seen in detail in the next section, it is even possible to treat tlic polar covalent nontransition-metal solids in this way. Thus we should be able to calculate properties of the transition-metal compounds just as we did for the simple ionic compounds. 

Tlie bands have long been interpreted as LCAO d bands, crossed by and hybridized with a free-electron-like band (Saffren, 1960 Hodges and Ehrenreich, 1965 and Mueller, 1967). By including some eleven parameters (pseudopotential matrix elements, interatomic matrix elements, orthogonality corrections, and hybridization parameters), it is possible to reproduce the known bands very accurately. We shall also make an LCAO analysis of the bands but shall take advantage of recent theoretical developments to reduce the number of independent parameters to two for each metal, each of which can be obtained for any metal from the Solid State Table. These two parameters will also provide the basis for understanding a variety of properties of the transition metals. 

In studying the properties of the transition metals it is most convenient to... 

Valence properties of the transition metal or main group element fragments can be changed by variation of element identity and by changing the external ligands. 

But now that many metals may be incorporated into such a framework, examples of all three possible isomers are known for this structure type. Indeed, two have been isolated for Rh, and in this case, the relative stabilities of the two isomers were determined to be 5p > Sq. If one assumes that the isomeric form isolated in the other cases corresponds to the most stable one, then isomer stability is seen to depend on the nature of the metal and its ancillary ligands. The properties of the transition metal are expressed in structure. 

Nowadays these questions are in the focus of attention in the studies of the magnetic properties of the transition metal oxides and of the colossal magnetoresistance compounds in part. For the LaMnOa crystals the most consistent approach based on taking into account both the CJTE and the superexchange Hamiltonians was developed by Ishihara, Inoue, and Maekawa [35]. 

Let s begin by surveying some of the key physical and chemical properties of the transition-metal elements and interpreting trends in those properties using the quantum theory of atomic structure developed in Chapter 5. We focus initially on the fourth-period elements, also called the first transition series (those from scandium through zinc in which the 3d shell is progressively filled). Then we discuss the periodic trends in the melting points and atomic radii of the second and third transition series elements. 

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