Electroneutrality principle

Paufing s electroneutrality principle is an approximate method of estimating the charge distribution in molecules and complex ions. It states that the distribution of charge in a molecule or ion is such that the charge on any single atom is within the range - -1 to —1 (ideally close to zero). 

Let us now examine the consequences of the formation of a donor-acceptor bond in a little more detail. If the donor - acceptor bond is completely covalent, then we record net transfer of one unit of charge from the donor to the acceptor as a direct consequence of the equal sharing of the electron pair between the two centres. This result leaves a positive charge on the donor atom and a negative charge on the acceptor atom. The limiting ionic and covalent descriptions of a complex cation such as [Fe(H20)6] are shown in Fig. 1-1. 

Colour of light absorbed Approximate wavelength ranges / nm Corresponding wavenumbers (approximate values) / cm Colour of light transmitted, i.e. complementary colour of the absorbed light 

In a colour wheel representation, complementary colours are in opposite sectors 

The intense colours of species such as [Mn04] have a different origin, namely charge transfer absorptions or emissions (see Section 16.4). The latter are not subject to selection rule 19.4 and are always more intense than electronic transitions between different d orbitals. We return to selection rules in Section 20.6. 

and the end of Section 1.12) compounds of J-block metals is common and arises from the presence of unpaired electrons. This phenomenon can be investigated using electron spin resonance (ESR) spectroscopy. It also leads to signal broadening and anomalous chemical shift values in NMR spectra (see Box 2.5). 

The formation of such complexes is analogous to the formation of those of s- and /j-block metals and discussed in previous chapters, e.g. [K(18-crown-6)]+, [Be(H20)4] +, fra -[SrBr2(py)5], [AlFg] , [SnCle] and [Bi2(C6H402)4] . 

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In principle, the effects of the concentration of ions can be removed by dividing A2.4.31 by the concentration. Taking Avagadro s constant as L and assuming a concentration of solute c mol m, then from the electroneutrality principle we have = A = z cL and clearly... 

According to the electroneutrality principle for this system, Ch = Ca + Cqh and = Ca + Cqh subtracting these equations gives... 

A few years ago3 71 proposed an electroneutrality principle—the postulate that the electron distribution in stable molecules and crystals is such that the electrical charge that is associated with each atom is close to zero, and in all cases less than 1, in electronic units. In a molecule involving single bonds we expect a transfer of charge from atom to... 

The transfer of an electron to the iron atom is compatible with the electroneutrality principle. The electronegativity of iron is 1.8, leading to 12% ionic character of the iron-carbon bonds and to the satisfactory value +0.04 for the resultant charge on an iron atom that has accepted an electron and is forming nine bonds with carbon atoms. 

The development during the past year of a statistical theory of unsynchronized resonance of covalent bonds in a metal, with atoms restricted by the electroneutrality principle to forming bonds only in number u — 1, u, and v + 1, with u the metallic valence, has led directly to the value 0.70 0.02 for the number of metallic orbitals per atom.39 This theory also has led to the conclusions that stability of a metal or alloy increases with increase in the ligancy and that for a given value of the ligancy, stability is a maxi-... 

Here the phosphorus atom has four shared electron pairs and one unshared pair, using five orbitals. (In PC15, eg, the transargononic phosphorus atom has five shared pairs in its outer shell.) However, because of the electroneutrality principle such a structure is allowed only for structure 1. Transargononic structures do not occur for first-row atoms, so this phenomenon is not found in NF3. These ideas concerning the bonding in NF3 and PF3 are implicit in the discussion by Marynick, Rosen and Liebman61 of the inversion barriers of these molecules. 

In the discussion of hypoelectronic metals in ref. 4, the number of ways of distributing Nv/2 bonds among NL/2 positions in a crystal containing N atoms with valence v and ligancy L was evaluated. The number per atom is the Nth root of this quantity. Structures for which the number of bonds on any atom is other than v-l,v, orv + l were then eliminated with use of the binomial distribution function [only the charge states M+, M°, and M are allowed by the electroneutrality principle (5)]. In this way the following expression for rhypo, the number of resonance structures per atom for a hypoelectronic metal, was obtained ... 

The compound Lajln has Tc = 10.4 K. Because La is hypoelectronic and In is hyperelectronic, I expect electron transfer to take place to the extent allowed by the approximate electroneutrality principle.13 The unit cube would then consist of 2 La, La, and In+, with In+ having no need for a metallic orbital and thus having valence 6 with the bonds showing mainly pivoting resonance among the twelve positions. The increase in valence of In and also of La (to 3 f ) and the assumption of the densely packed A15 structure account for the decrease in volume by 14.3%. Because the holes are fixed on the In + atoms, only the electrons move with the phonon, explaining the increase in Tc. 

Accordingly, the CO moiety acquires negative charge. The consequent exigencies of the electroneutrality principle are then met by the CO group donating this charge back to the metal via its now expanded <7-donor orbital ... 

Consider the closely related ion [FeCHiO/e] ". The only difference is in the formal oxidation state of the metal ion. If an ionic model is assumed (9.6), the charge on the metal center is +2. A purely covalent model results in the placing of a formal quadruple negative charge upon the iron center (9.7). To satisfy the electroneutrality principle, and establish a near-zero charge on the metal, each oxygen atom is... 

Attempts to rationalize the role of ligands in these reactions and in the even more intriguing case of cooligomerizations have been successful only in part. Steric and electronic effects of the substrate should not be considered without taking in account both the other ligands present and the oxidation state of the metal. Donor substrates are generally best stabilized by acceptor ligands and vice versa (10c). in accordance with the electroneutrality principle. 

Structure (3.226c), for example, depicts a central heptavalent Cl atom (Fa = 7), exceeding the normal valence octet by six electrons (These excess electrons are assumed to be accommodated in chlorine 3d orbitals, whereas d-orbital participation is prevented in first-row compounds.) Hypervalent structures such as (3.226a)-(3.226c) are claimed to be justified by the electroneutrality principle, which stipulates that second-row central atoms have zero formal charge (whereas first-row oxyanion Lewis structures commonly violate this principle).148... 

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