Main-group elements electronegativity

This type of transhalogenation reaction, which is common amongst the halides of main group elements, always proceeds in the direction which pairs the most electropositive element with the most electronegative, since the greatest amount of energy is evolved with this combination. 

Table 2.1 Values of electronegativity x for some main-group elements...

Zintl phases remarks on their definition. We have seen that the Zintl phases may be considered as a group of compounds formed by an electropositive (cationic) component (alkali, alkaline earth metal, lanthanide) and an anionic component (for instance a main group element of moderate electronegativity). The anionic part of the structure may be described in terms of normal valence combination. 

Reductive elimination is simply the reverse reaction of oxidative addition the formal valence state of the metal is reduced by two (or one in a bimetallic reaction), and the total electron count of the complex is reduced by two. While oxidative addition can also be observed for main group elements, this reaction is more typical of the transition elements in particular the electronegative, noble metals. In a catalytic cycle the two reactions always occur pair-wise. In one step the oxidative addition occurs, followed for example by insertion reactions, and then the cycle is completed by a reductive elimination of the product. 

Figure 1.7 The Allred-Rochow electronegativity coefficients of the main group elements of the 2nd, 3rd, 4th and 5th periods...

Figure 3.7 shows the relationship between atomic size and electronegativity for the main-group elements in periods 2 to 6. 

Table 6.5 Electronegativities of Some Main Group Elements...

Figure 3. Electronegativity EN (according to Allred-Rochow) and the X-C-C angles (MP2/6-31G black dots experimental data triangles) of ethyl-main-group elements (eel. = eclipsed, stag. = staggered, perp. = perpendicular). For more details see text and ref. [22].

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