Electronics chemical behaviour

The loose connection between electron configuration and the chemical behaviour of the heavy elements (transuranics). C. K. Jorgensen, Angew. Chem., Int. Ed. Engl., 1973,12,12-19 (73). 

In effect the chemist, and chemistry teacher, explains the observed chemical behaviour of matter (substances) - colour changes, precipitation from solution, characteristic flame colours, etc. - in terms of the very differenthQ miom of the quanticles that are considered to form the materials at the sub-microscopic level. Much of this involves the reconfiguration of systems of negative electrons and positively charged atomic cores (or kernels ) due to electrical interactions constrained by the allowed quantum states. 

Nano-structures comments on an example of extreme microstructure In a chapter entitled Materials in Extreme States , Cahn (2001) dedicated several comments to the extreme microstructures and summed up principles and technology of nano-structured materials. Historical remarks were cited starting from the early recognition that working at the nano-scale is truly different from traditional material science. The chemical behaviour and electronic structure change when dimensions are comparable to the length scale of electronic wave functions. Quantum effects do become important at this scale, as predicted by Lifshitz and Kosevich (1953). As for their nomenclature, notice that a piece of semiconductor which is very small in one, two- or three-dimensions, that is a confined structure, is called a quantum well, a quantum wire or a quantum dot, respectively. 

The atomic spectra of the actinides are very complex and it is difficult to identify levels in terms of quantum numbers and configurations (6). The chemical behaviour of the elements is dictated by the configurations of the electrons around the nucleus and in the case of the actinides it is the competition between the 5/ 1 7 s2 and the 5 /n 1 6 d 7 s2 levels that dictates these chemical properties. A comparison of the /-energy levels of the lanthanides and the actinides shows that less energy is required for the promotion of the 5 / -> 6 d levels than for the 4/ -> 5 d levels in the lanthanides. As a result of this lower energy requirement by the actinides they have the tendency to display higher valences since the bonding electrons are more readily available. It is only at the commencement of the second half of the actinides that there is commencement of properties which echo those of the lanthanides. 

As expected there is a close resemblance in the chemical behaviour of technetium and rhenium whereas the properties of both elements differ considerably from those of manganese. The electronic configuration of technetium in the ground state is 4d 5s. Technetium is a silver-grey metal which tarnishes slowly in moist air. 

Tellurium is the fourth element of the VIA family of the periodic table, which starts with oxygen. Since tellurium exhibits an electronic configuration similar to that of selenium and sulphur, the chemical behaviour of these elements is obviously closely related. This similarity was a hindrance to the greater development of tellurium chemistry. During several decades, research was restricted to an extrapolation of well-established reactions for the preparation and use of organic sulphur compounds to selenium, and mainly from selenium to tellurium. 

The molecular orbital picture of benzene proposes that the six jt electrons are no longer associated with particular bonds, but are effectively delocalized over the whole molecule, spread out via orbitals that span all six carbons. This picture allows us to appreciate the enhanced stability of an aromatic ring, and also, in due course, to understand the reactivity of aromatic systems. There is an alternative approach based on Lewis structures that is also of particular value in helping us to understand chemical behaviour. Because this method is simple and easy to apply, it is an approach we shall use frequently. This approach is based on what we term resonance structures. 

There are undoubtedly more elements on the way, as little by little the Periodic Table is extended into uncharted waters. And as this happens, we will learn about how these new elements behave. In 1997 an international team that included scientists from GSI, Berkeley, and Dubna was able to deduce that element 106 (seaborgium) has chemical properties similar to molybdenum and tungsten. In a sense this might have been expected, since seaborgium sits below these elements in the Periodic Table. But in fact the result was a surprise, because the chemical behaviour of the preceeding superheavy elements 104 and 105 is distorted by the effects of relativity on the electrons surrounding the immense nuclei. 

The chemical behaviour of an element depends on its electrons how many of them, and how arranged in their shell structure. The configuration of electrons is the same for all isotopes of an element - adding extra neutrons to a nucleus has essentially no effect on the electrons. So isotopes show the same chemical behaviour as one another. 

Another notable difference in properties down groups is the inert psiir effect > as demonstrated by the chemical behaviour of Tl, Pb and Bi. The main oxidation states of these elements are + I, + 2 and + 3, respectively, which are lower by two units than those expected from the behaviour of the lighter members of each group. There is a smaller, but similar, effect in the chemistry of In, Sn and Sb. These effects are partially explained by the relativistic effects on the appropriate ionization energies, which make the achievement of the higher oxidation states (the participation of the pair of s-electrons in chemical bonding) relatively more difficult. 

The chemical behaviour of molecules generally depends on the most weakly bound electrons. A molecule in the excited state differs from the ground state molecule with respect to both energy and electron wave-function, and therefore differs in its chemistry. Irradiation to produce an excited electronic state alters the reactivity of molecules in a number of ways which decide the nature of any photochemical reaction ... 

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