Metallic elements band theory

A pure transition metal is best described by the band theory of solids, as introduced in Chapter 10. In this model, the valence s and d electrons form extended bands of orbitals that are delocalized over the entire network of metal atoms. These valence electrons are easily removed, so most elements In the d block react readily to form compounds oxides such as Fc2 O3, sulfides such as ZnS, and mineral salts such as zircon, ZrSi O4. ... 

A simple alternative model, consistent with band theory, is the electron sea concept illustrated in Fig. 9-22 for sodium. The circles represent the sodium ions which occupy regular lattice positions (the second and fourth lines of atoms are in a plane below the first and third). The eleventh electron from each atom is broadly delocalized so that the space between sodium ions is filled with an electron sea of sufficient density to keep the crystal electrically neutral. The massive ions vibrate about the nominal positions in the electron sea, which holds them in place something like cherries in a bowl of gelatin. This model successfully accounts for the unusual properties of metals, such as the electrical conductivity and mechanical toughness. In many metals, particularly the transition elements, the picture is more complicated, with some electrons participating in local bonding in addition to the delocalized electrons. 

Crystal field theory is one of several chemical bonding models and one that is applicable solely to the transition metal and lanthanide elements. The theory, which utilizes thermodynamic data obtained from absorption bands in the visible and near-infrared regions of the electromagnetic spectrum, has met with widespread applications and successful interpretations of diverse physical and chemical properties of elements of the first transition series. These elements comprise scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper. The position of the first transition series in the periodic table is shown in fig. 1.1. Transition elements constitute almost forty weight per cent, or eighteen atom per cent, of the Earth (Appendix 1) and occur in most minerals in the Crust, Mantle and Core. As a result, there are many aspects of transition metal geochemistry that are amenable to interpretation by crystal field theory. 

The hydrogen overpotential of metals periodically changes, and specifically Pt-G elements. Re and Tc show lower overpotentials. One can explain those in referring to tZ-hole characteristics based on the band theory. For utilization of RMFP, hydrogen evolution characteristic of the RMFP-deposit on Pt electrodes was investigated for electrolysis in alkaline solution. 

Recombination luminiscence is used, of course, to a limited extent, in luminiscence analysis of inorganic substances to detect trace amounts of a large number of elements. Recombination crystallophosphors, for example sulfides, are ionic crystals consisting of matrix (CaS, SrS, ZnS, CdS and others) whose crystalline lattice may easily suffer distortion on the introduction of minute amounts of metal ions (like Ag+, Cu2+, Mn2+ etc.) called activators. The mechanism of this luminiscence is explained in terms of the band theory of solids54 56). 

There are irregularities, however. In the transition metal groups 7, 8 and 9 the 3d series elements Mn, Fe and Co are exceptions. Some elements also have more complex structures, especially in thep block. An understanding of the factors controlling metallic structures requires the band theory of delocalized electrons, not discussed in this book. 

In Section 11.6 we saw that the ability of metals to condnct heat and electricity can be explained with molecular orbital theory. To gain a better nnderstanding of the conductivity properties of metals we must also apply our knowledge of qnantnm mechanics. The model we will use to study metallic bonding is band theory, so called becanse it states that delocalized electrons move freely through bands formed by overlapping molecular orbitals. We will also apply band theory to certain elements that are semiconductors. 

Describe the three types of cubic unit cells and explain how to find the number of particles in each and how packing of spheres gives rise to each calculate the atomic radius of an element from its density and crystal structure distinguish the types of crystalline solids explain how the electron-sea model and band theory account for the properties of metals and how the size of the energy gap explains the conductivity of substances ( 12.6) (SP 12.4) (EPs 12.57-12.75)... 

A simplified version of band theory can therefore be used to make a rather sweeping generalization about the electrical properties of the elements, as shown in Figure 11.48. One primary difference between the metals and nonmetals is related... 

Group 14 of the Elements Handbook (Appendix A) contains a discussion of semiconductors and the band theory of metals. How does this model explain the electrical conductivity of metals ... 

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