Silicon nonbonding electron pairs

Figure 12.20 By drawing Lewis structures you can show that there are three (chlorine), two (sulfur), one (phosphorus), and zero (silicon) nonbonding electron pairs per atom.

Silicon (Si) and germanium (Ge) are in the same group of the periodic table as carbon, and they form tetrahedral compounds as carbon does. When four different groups are situated around the central atom in silicon, germanium and nitrogen compounds, the molecules are chiral. Sulphoxides, where one of the four groups is a nonbonding electron pair, are also chiral. 

Wurtz coupling of dibutylaminotrimethyl-l-2-dichlorodisilane forms a partially networked polymer.79 This networked polymer shows an absorption maximum at 360 nm, that is 30 nm red shifted relative to the absorption of poly (dialkylsilanes). The shift is due to the nonbonding electron pair of the amino substituents extending the a-conjugation of the silicon backbone. Two broad emission bands at 440 nm and 400 nm are observed and assigned to the network silicon units and the linear silicon chains, respectively. The unusual photophysical properties arise from both the amino side groups and the networked structure. 

How many nonbonding electron pairs are there per atom in chlorine, sulfur, phosphorus, and silicon ... 

The most striking property of water is that its solid form is less dense than its liquid form ice floats at the surface of liquid water (Figure 6.8). With a few exceptions, (for example, silicon, gallium, germanium, bismuth, and pure acetic acid), the density of almost all other substances is greater in the solid state than in the liquid state. To understand why water is different, we have to examine the electronic structure of the H2O molecule. As we saw in Chapters 2 and 3, there are two pairs of nonbonding electrons, or two lone pairs, on the oxygen atom ... 

It has been known for some time that the basicities of a heteroatom decrease upon a-silyl substitution [12], For example, alkyl silyl ethers (R3Si-0-R ) are less basic than dialkly ethers. Silylamines are weak bases compared to alkylam-ines. This electron-withdrawing effect of silyl groups has been explained in terms of the interaction between low lying vacant orbitals such as 3d orbitals of silicon or a orbitals with the nonbonding p orbitals (lone pairs) of the heteroatom (Fig. 4). This interaction decreases the HOMO level which in turn lowers the basicity of the heteroatom. Such effect may also cause the increase of the oxidation potentials, but little study has been reported on the electrochemical properties of this type of compounds. 

All of the nonbond potential functional forms that have been presented to this point take into account the effect that one particle has on another particle based solely on the distance between the two particles. However, in some systems like metals and alloys as well as some covalently bonded materials like silicon and carbon, the nonbonded potential is a function of more than just the distance between two particles. In order to model these systems, the embedded-atom method (EAM) (Daw and Baskes 1983,1984 Finnis and Sinclair 1984) and modified embedded-atom method (MEAM) (Baskes 1992) utilize an embedding energy, f j, which is a function of the atomic electronic density pi of the embedded atom I and a pair potential interaction 0// such that... 

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