Inert pair of electrons

On the other hand, there are good reasons for believing that this is not always the case and with, for example, antimony and bismuth, the heavier members of the group, there is evidence for the presence of an inert pair of s electrons. Because the angles between the substituents of a neutral antimony(III) or bismuth(III) compound are close to 90°, it is possible to consider that, rather than using sp hydrid orbitals, the substituents are attached via pure p orbitals, with the lone pair of electrons remaining localized in the appropriate s orbital. The concept of an inert pair of electrons has some validity and it allows rationalization of much of the chemistry of these elements in the + 3 oxidation state. It is, however, difficult to provide direct experimental evidence for the effect, but it is difficult otherwise to rationalize the almost ideal octahedral structure of [SbClg]. ... 

There are a number of features that will be evident from the structures described herein that help illustrate the role that the inert pair of electrons plays in these structures. Some of the motifs will include the formation of polar structures where the oxoanions are aligned along one crystallographic axis, and the creation of channels to house the lone-pair electrons, which in at least one case gives rise to a chiral network. 

The central question that needs answering as this chapter comes to a close is whether or not general statements can be made concerning the role that the inert pair of electrons on heavy oxoanions can play in determining the structures of crystalline actinide compounds As we survey the known materials with anions of this type, it is apparent that there are many roles for these electrons, including the formation of channels and cavities, alignment to create polarity and chirality, and especially dimensional reduction. Dimensional reduction to one-... 

FIG. 12.14. The crystal structure of tetragonal PbO (and SnO). The small shaded circles represent metal atoms. The arrangement of bonds from a metal atom is shown at the right, where the two dots represent the inert pair of electrons (see p. 937). 

These compounds of tetrapositive lead correspond to the tin compounds prepared in Experiment 19. Compounds of tetrapositive lead are much less stable than compounds of tetrapositive tin, owing to the greater inertness of the so-called inert pair of electrons in the atom of lead (see Chapter VI) that is, +4 lead will gain two electrons very easily to form +2 lead. This property is very apparent in this experiment. 

Lead(II) in Group IV and bismuth(III) in Group V we saw that the stability of the oxidation number that is two less than the Group number increases down Groups III, IV and V. Thus, in Groups IV and V, lead and bismuth are the elements in which it should be most prominent. Note that lead(II) and bismuth (III) are the oxidation numbers that are associated with the T1+ electronic configuration, [Xe]4f " 5d 6s, which contains an inert pair of electrons in the 6s subshell. The conclusion is correct lead(IV) and bismuth(V) are even less stable with respect to lead(II) and bismuth(III) than thallium(III) is with respect to thallium(I). 

The classical view of the lone pair is that, after mixing of the s and p orbitals on the heavy metal cation, the lone pair occupies an inert orbital in the ligand sphere [6]. This pair of electrons is considered chemically inert but stereochemi-cally active [7]. However, this implies that the lone pair would always and in any (chemical) environment be stereochemically active, which is not the case. For example, TIF [8] adopts a structure, which can be considered as a NaCl type of structure which is distorted by a stereochemically active lone pair on thallium. In contrast TlCl [9] and TlBr [10] adopt the undistorted CsCl type of structure at ambient temperature, and at lower temperatures the (again undistorted) NaCl type of structure. The structure of PbO [11] is clearly characterized by the stereochemically active lone pair. In all the other 1 1 compounds of lead with... 

Three pairs of electrons must be shared in order that each nitrogen atom has an octet of electrons. The formation of strong covalent bonds between nitrogen atoms in N2 is responsible for the relative inertness of nitrogen gas. 

The fact that SFs does not react with water is not due to thermodynamic stability. Rather, it is because there is no low-energy pathway for the reaction to take place (kinetic stability). Six fluorine atoms surrounding the sulfur atom effectively prevent attack, and the sulfur atom has no unshared pairs of electrons where other molecules might attack. In SF4, not only is there sufficient space for an attacking species to gain access to the sulfur atom, but also the unshared pair is a reactive site. As a result of these structural differences, SF6 is relatively inert, whereas SF4 is very reactive. 

NHCs possess a lone pair of electrons and an accessible vacant orbital. This combination resembles the situation in many transition metal centers and could thus mimic their chemical behavior. While cyclic diaminocarbenes are inert towards hydrogen, it has been demonstrated that cyclic (aIkyl)(amino)carbenes of type 16... 

The octalluoroxenaies are the most stable xenon compounds known they can be heated to 400 °C without decomposition. The anions have square antiprismatic geometry. They, too, present a problem to VSEPR theory analogous to that of XeF6 since they should also have a stereochemically active lone pair of electrons that should lower the symmetry of the anion. If the steric crowding theory is correct, however, the presence of eight ligand atom/, could force the lone pair into a stereochemically inert s Orhital. 

The atoms of each of the elements of Group IVb have four valence electrons, two of them s electrons, two of them p electrons. Although these are seldom, if ever, completely removed, they are very often shared with electronegative elements, leading to the +4 oxidation state which may be considered typical of the family. As indicated earlier, however (p. 121), the two electrons sometimes remain aloof when this happens, the elements assume the +2 state. The stability of the +2 state (which is related to the degree of aloofness of the so-called inert pair of s electrons) increases sharply with atomic number. The values of the oxidation potentials for the change M 2 —> M+4 mirror this trend ... 

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