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The elements to be treated in this chapter may be considered to be of three types. All of them show one species which dominates the water domain in the E–pH diagram. The dominant species in the E–pH diagrams and the elements which display it are as follows: (1) an insoluble oxide: Ti, Zr, Hf (Group 4B) and Nb, Ta (Group 5B), (2) a high-oxidation-state anion: Mo, W (Group 6B) and Tc, Re (Group 7B), (3) a noble metal: Ru, Rh, Pd, Os, Ir, Pt (Group 8B). These five elements all show highly stable inert oxides which occupy the majority of the water domain in their E–pH diagrams. This can be seen in Figures 13.1 through 13.5. The three 4B oxides (TiO₂, ZrO₂, HfO₂) are insoluble in HOH, dilute acids, dilute bases, and concentrated bases, but are soluble in strong concentrated acids to give TiO+2, ZrO+2, and HfO+2. The two 5B oxides (Nb2O5, Ta2O5) are insoluble in HOH, dilute acids, and dilute bases, but Nb2O5 dissolves in concentrated bases whereas Ta2O5 does not. All the elements in their highest oxidation state are hard cations and therefore will be particularly attracted to the hard atoms F and O. a. E–pH diagram. The E–pH diagram in Figure 13.1 shows Ti in oxidation states of 0, II, III, and IV. In the legend of the diagram, equations for the lines between the species are presented. Table 13.1 displays ions and compounds of Ti. The metal appears to be very active, but a thin refractory oxide coating renders it inactive to all but extreme treatment. Ions and compounds in oxidation states of II and III are unstable with regard to atmospheric O₂ and also with regard to HOH except for Ti+3 in strongly acidic solution. b. Discovery, occurrence, and extraction. Ti, named after the Titans, the mythological first sons of the earth, was discovered by Gregor in 1791 in the mineral menachanite, a variety of ilmenite. The major sources of Ti are the minerals rutile TiO₂ and ilmenite FeTiO3. They are treated with Cl2 and C at elevated temperatures to generate gaseous TiCl4 which condenses to a colorless liquid at 136°C.

The supply of the known 118 elements is considered in terms of their abundance in the universe and in the Earth?’s crust, the availability of minerals and their formation of elements from natural and induced transmutation. The blocks of the elements of the Periodic Table are analysed to consider whether their availability is such that can allow them to participate in solutions of the pressure on resources on the Earth. The roles of the elementary properties, radii, ionisation energies and electronegativities in affording the characteristics of the elements, including conductivity properties, are explained. The factors influencing the properties of compounds that affect their modes of extraction, such as their energetics, solubility and oxidation state stability are also discussed.

After solving a structure, the crystallographer has to find a sensible interpretation of the solution, as the initial model is usually merely a collection of unidentified peaks. The crystallographer needs to find out which density maximum corresponds to which chemical element, a task that would be easy if the electron density peaks were somehow colour-coded and electron density for carbon was, say, black, for nitrogen blue, for sulfur yellow, for oxygen red and so forth. Unfortunately all electrons are blue, at least on the computer screen, and this chapter describes crystallographic (e.g., thermal parameters, bond lengths) and chemical knowledge (e.g., oxidation states, coordination geometry) necessary for atom type assignment. Three examples are given in which the assignment of the atom type is not quite obvious.

This chapter investigates the modulation of synaptic N-methyl D-aspartate (NMDA) receptors in striatal medium spiny neurons by the presence of endogenous dopamine. It demonstrates that an interaction is occurring between ascorbate and dopamine. It also illustrates that ascorbate could facilitate the lifetime of dopamine acting synaptically by altering the oxidation state of dopamine (DA). This chapter then shows a novel regulation of NMDA receptor-mediated synaptic responses that may have relevance for neurological diseases of the basal ganglia.