| Summary: | The elements which constitute the Carbon Group of the Periodic Table are carbon C, silicon Si, germanium Ge, tin Sn, and lead Pb. All five of the elements have atoms characterized by an outer electron structure of ns2np2 with n representing the principal quantum number. This electron arrangement signals the possibility of oxidation states of IV and II. Such is the case with the II oxidation state becoming more stable from C to Pb. As one descends the group, there is a marked change from non-metallic (C) to metallic character (Pb). Reflecting very high ionization energies, C, Si, and Ge do not form a simple cation, they instead bond covalently. In line with the trends just mentioned, the inorganic aqueous chemistry moves from anionic (C) to cationic (Pb). The inorganic aqueous solution chemistry of C is represented by four acids and their anionic derivatives: carbonic acid H2CO3, oxalic acid H2C2O4, formic acid HOOCH, and acetic acid HOOCCH3. Note that in all of these the ionizing H+ ions are not attached to C but to O. The inorganic aqueous chemistry of Si is dominated by anions SiO(OH)3− and SiO2(OH)2−2 and their many polymeric forms and by the hexafluorosilicate anion SiF6−2. Ge is very similar to Si. Cationic species, largely absent in all three previous elements, are shown in both Sn and Pb. The covalent single bond radii of C, Si, and Ge are 77, 118, and 122 pm, and the ionic radii in pm of the other two elements are Sn+2(118), Sn+4 (83), Pb+2 (133), Pb+4 (92). a. E–pH diagrams. In order to understand the E–pH relationships of the aqueous species of C, it is important to consider both the thermodynamic and the kinetic relationships. Thermodynamics tells us whether a reaction will occur but it says nothing about how fast. The rate is a kinetic matter. When acetic acid HC2H3O2 is entered into a C species E–pH diagram, Figure 8.1 results. This figure shows that at equilibrium HC2H3O2 is not stable and disproportionates into H2CO3 and CH4. The same E–pH diagram results when formic acid HOOCH or when oxalic acid ...
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