Charge alternation concept

This scheme is actually much more comphcated than the scientific model of silver ions sticking to chloride ions because of their opposite charges (Figure 4.7) and illustrates just how tenacious some misconceptions can be once they have a hold of a student s imagination. You can download a diagnostic task to identify common alternative conceptions students may hold about how bonds form in a precipitation reaction ( Reaction to form silver chloride ) from the Royal Society of Chemistry website (see the Other resources section at the end of this chapter). 

The concepts of resonance and charge alternation are nearly synonyms and useful for the description of electron distribution of conjugated % systems bound to heteroatoms [1, 2]. Alternation of the charge along a saturated chain was definitively confirmed by the semiempirical CNDO/2 method [3]. 

Wellington, C.A. Khowaiter, S.H. Charge Distributions in Molecules and Ions MINDO 3 Calculations. An Alternative of the Charge Localization Concept in Mass Spectrometry. Tetrahedron 1978,34,2183-2190. 

Secondly, in the symbolic phase, it is important to pay extra attention to reaction equations, especially the writing of formula-units of salts. To avoid students alternative conception that salts do not consist of ions because of the absence of charge in the formulas, it is better to put these charges in the formulas. For instance, in the beginning of teaching precipitation reactions, you can better write the precipitation reaction for silver chloride as Ag (aq) + CT(aq) —> Ag CF(s). When students are more familiar with writing salt formulas you can replace Ag Cl (s) by the simple AgCl(s) notation. 

More recently, a new method of assembling multilayers of PB on surfaces has been described.110 In contrast to the familiar process of self-assembly, which is spontaneous and leads to single monolayers, directed assembly is driven by the experimenter and leads to extended multilayers. In a proof-of-concept experiment, the generation of multilayers of Prussian blue (and the mixed Fein/Run analog ruthenium purple) on gold surfaces by exposing them alternately to positively charged ferric cations and [Fe(CN)6]4- or [Ru(CN)f,]4 anions has been demonstrated.110... 

In 1997, Decher reported a fundamental concept regarding the multilayer nanoassemblies composed of polycations and polyanions [24]. The polymer assemblies were prepared by an alternate adsorption process, as shown in Figure 6.5. If a substrate has an anionic charge on its surface then polycation could adsorb onto the surface as a first layer. Polyanion could subsequently adsorb onto the surface by immersing in a... 

The second reactions represented in Schemes 5.15 and 5.16 deal with the same initial ion and the same products. The essence consists in the question, which of two complementary particles retains the charge To estimate the intensity of the alternative peaks one should use Stevenson s mle (Section 5.4.1.2). To propose a mechanism of the process (in terms of the described concept) it is necessary to take into account that stabilization of the charge is more important than stabilization of the radical (see above). As the reactions initiated by the charge involve charge migration, they are usually less favorable in comparison with the alternative reactions initiated by the radical center. 

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