Main-group elements oxidation states/numbers

Table 63 Ionic radii for main group elements according to Shannon [69], based on r(Oz ) = 140 pm. Numbers with signs oxidation states. All values refer to coordination number 6 (except c.n. 4...

In subsequent research, it turned out that two-state reactivity can also provide a concept for the understanding of oxidation reactions way beyond the scope of gas-phase ion chemistry and can actually resolve a number of existing mechanistic puzzles. In enzymatic oxidations involving cytochrome P450, for example, changes in spin multiplicity appear to act as a kind of mechanistic distributor for product formation [27-29], and in the case of manganese-catalyzed epoxidation reactions, two-state scenarios have been put forward to account for the experimentally observed stereoselectivities [30-32], Two-state reactivity is not restricted to oxidation reactions, and similar scenarios have been proposed for a number of other experimentally studied reactions of 3d metal compounds [33-37]. Moreover, two-state scenarios have recently also been involved in the chemistry of main group elements [38]. The concept of two-state reactivity developed from the four-atomic system FeO /H2... 

One of the classical properties of the main group elements is that the stability of the lower oxidation states increases with atomic number, and the chemistry of thallium is a good example of this effect. In aqueous solution, the Tl+ ion is stable with respect to oxidation by the solvent and there is accordingly an extensive chemistry of this oxidation state. The similarities between Tl+ and the corresponding alkali metal cations have resulted in much interest in the use of this ion as a probe in biochemical systems, and the ease with which 205T1 NMR spectra can be recorded has also had an impact on such studies.277,278... 

The change in the basic and acidic properties here shown for the oxides of main group elements which have the highest oxidation state number. The oxides in the blue colored regions are basic (metallic) oxides and the oxides in the red colored regions are acidic (nonmetallic) oxides. The oxides in both blue and red colored regions are amphoteric oxides (the oxides of amphoteric metals). 

The concept of an atom s oxidation state see Oxidation Number) can provide fundamental information about the stmcture and reactivity of the compound in which the atom is found. In fact, it can be argued that oxidation states provided the basis for Medeleev s initial organization of the periodic table. For the main group elements, the relative stability of lower oxidation states within a given group increases as the atomic number increases. This trend in the periodic table see Periodic Table Trends in the Properties of the Elements) is generally attributable to the presence of an inert s pair see Inert Pair Effect) caused by relativistic effects see Relativistic Effects). 

Multiple oxidation states are characteristic of the transition elements. Remember that iron gives up two electrons and forms the Fe + ion in its oxide, FeO. In another oxide, Fe203, iron gives up its two 4s electrons and one 3d electron to form the Fe ion. Many of the transition elements can have multiple oxidation numbers ranging from 2+ to 7+. These oxidation numbers are due to involvement of the d electrons in chemical bonding. Recall that only some of the heavier main group elements such as tin, lead, and bismuth have multiple oxidation numbers. These elements also have d electrons that can be involved in bonding. 

An important group of cations that shows electronically distorted environments are those of the main group elements in lower oxidation states. These contain nonbonding electron pairs in their valence shells, the so-called lone pairs . Such atoms are usually found displaced from the center of their coordination sphere so as to form between 3 and 5 strong bonds and a number of weaker ones. The effect can be described using the Valence Shell Electron Pair Repulsion (VSEPR) Model [43] in which it is assumed that the cation is surrounded uniformly by between 4 and 7 electron pairs occupying valence shell orbitals. One or more of these is a lone pair... 

A number of the distortions found in cation coordination environments are the result of electronic instabilities in the atoms themselves. Such distortions are typically found among the transition metal cations and the main group elements in low oxidation states. The origins of these instabilities are different and they... 

The main group elements show a periodic pattern of oxidation states. For the first 25 elements, there is a stepwise increase in the oxidation state for the elements as you follow them going across the periodic table, left to right, as shown in Figure 3-1. The maximum oxidation state of an element is equal to the number of electrons in the outer orbital for these first 25 elements. 

The transition metals often have a variety of oxidation states and usually have an oxidation state that s less than that of their group number. The oxidation state of the main group elements, however, is usually the same as the group number. For example, the main group elements Na, Mg, and AF all have a single oxidation state that s the same as their respective group numbers. 

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