The Transition Metals and Their Compounds

In this chapter we shall discuss the chemistry of the transition metals— the elements that occur in the central region of the periodic table. These elements and their compounds have great practical importance. Their chemical properties are complex and interesting. 

The Electronic Structures and Oxidation States of Iron Cobalt, Nickel, and the Platinum Metals 

It might be expected that the two outermost electrons would be easily removed, to form a bipositive ion. In fact, iron, cobalt, and nickel all form important series of compounds in which the metal is bipositive. These metals also have one or more higher oxidation states. The platinum metals form covalent compounds representing various oxidation states between +2 and +8. 

Iron can assume the oxidation states+2, +3, and +6, the last being rare, and represented by only a few compounds, such as potassium ferrate, KaFeOj. The oxidation states +2 and +3 correspond to the ferrous ion, Fe , and ferric ion, Fe, respectively. The ferrous ion has six electrons in the incomplete 2 d subshell, and the ferric ion has five electrons in this subshell. The magnetic properties of the compounds of iron and other transition elements are due to the presence of a smaller number of electrons in the 3td subshell than required to fill this subshell. For example, ferric ion can have all five of its 2 d electrons with spins oriented in the same direction, because there are five 2 d orbitals in the 3d subshell, and the Pauli principle permits parallel orientation of the spins of electrons so long as there is only one electron per orbital. The ferrous ion. is easily oxidized to ferric ion by air or other oxidizing agents. Both bipositive and terpositive iron form complexes, such as the ferrocyanide ion, Fe(CN)e and the ferricyanide ion, Fe(CN)e, but they do not form complexes with ammonia. 

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This brief review has shown that the transition metals and their compounds can play a very useful role in ceramics-directed silicon chemistry. Transition metal complexes find important applications as catalysts as well as stoichiometric reactants, and the metals themselves have found more direct application in the synthesis of silicon-containing ceramics and ceramic composites. 

In Chapter III the basic physical ideas inherent in these theories are applied to the transition metals and their compounds and alloys. These applications are separated into three main categories materials with R > Rc, those with R Rc, and those with R < Rc. Materials... 

A proper description of electronic defects in terms of simple point defect chemistry is even more complicated as the d electrons of the transition metals and their compounds are intermediate between localized and delocalized behaviour. Recent analysis of the redox thermodynamics of Lao.8Sro,2Co03. based upon data from coulometric titration measurements supports itinerant behaviour of the electronic charge carriers in this compound [172]. The analysis was based on the partial molar enthalpy and entropy of the oxygen incorporation reaction, which can be evaluated from changes in emf with temperature at different oxygen (non-)stoichiometries. The experimental value of the partial molar entropy (free formation entropy) of oxygen incorporation, Asq, could be... 

The transition metals and their compounds are well-known for their catalytic properties. The works related to catalytic applications involving metallic compounds have been awarded about 15 Nobel prizes between 1901 and 2014. While the idea of catalysis was originally conceived by Berzebus, it was... 

This process is thermodynamically favorable. It has a Mt of-98.2 kJ-mol and a ACT of-119.2 kJ mor and a AS of 70.5 TmoP -K . The rate of decomposition is dependent on the temperature and concentration of the peroxide, as well as the pH and the presence of impurities and stabilizers. Hydrogen peroxide is incompatible with many substances that catalyse its decomposition, including most of the transition metals and their compounds. Common catalysts include manganese dioxide, silver, and platinum. The same reaction is catalysed by the enzyme catalase, found in the liver, whose main function in the body is the removal of toxic byproducts of metabolism and the reduction of oxidative stress. The decomposition occurs more rapidly in alkali, so acid is often added as a stabilizer. 

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