Atomic properties, carbon compared with silicon

Similarities and differences between Ge, Sn, Pb (M) atoms and their M—Y bonds (Y = inorganic, organic or organometallic substituents). In some cases the specific character of the M atom and the M—Y bonds is more clearly seen when compared with properties and bonds of carbon and especially silicon atoms — the lighter elements of the group 14 column of the periodic table. The peculiarities of M atoms and M—Y bonds determine to a considerable extent the similarity and difference of the physical properties and chemical behaviour of organic compounds of the elements in question. 

The continuous reduction in size of a solid finally leads to a situation where the original solid state properties can be only partially observed or may be even completely lost, as these properties are exclusively the result of the cooperation between an infinite number of building blocks. Further reduction of size finally leads to typical molecular behavior. On the other hand, even here are structural relations to the bulk occasionally detectable. For instance, the arrangements of the sp hybridized carbon atoms in cyclohexane or in adamantane can easily be traced back to the diamond lattice, whereas benzene or phenanthrene represent derivatives of the graphite lattice. However, neither cyclohexane, benzene, nor phenanthrene have chemical properties which are comparable with those of the carbon modifications they originate from. The existence of the above mentioned Q, C]o or Ci4 units is otUy made possible by the saturation of the free valencies by hydrogen atoms. Comparable well known examples for other elements are numerous, for instance the elements boron, silicon, and phosphorous. Figure 1-1 illustrates some of the relations between elementary and molecular structures. 

Chapter 6 addresses the stracture of non-polymer fibers. A wide range of non-polymer fibers, such as carbon, glass, silicon carbide, boron, asbestos, and metal fibers, now is available commercially. Compared with polymer fibers, nonpolymer fibers often are stronger, stiffer, more heat resistant, and nonflammable. However, except for metal fibers, non-polymer fibers also are characterized by their brittleness. These property characteristics are directly related to the atomic arrangement and the defect stracture of non-polymer fibers. Chapter 6 discusses the stracture of two most used non-polymer fibers caibon and glass fibers. 

Cl, O, S, N) or Si—M—X (M C) groups, it was demonstrated that a number of anomalous physicochemical properties exist as compared to carbon analogs (a-effect). This is due to the fact that the interaction of Si and X atoms follows not only the inductive and resonance mechanisms but can also occur through space 614,617,619) jjj jjjg jjg silicon atom can interact either directly with X... 

Selected physical properties of the tetrahalides of C and Si are listed in Table 13.3. The carbon tetrahalides differ markedly from those of the later group 14 elements they are inert towards water and dilute alkali and do not form complexes with metal halides. The distinction has been attributed to the absence of d orbitals in the valence shell of a C atom look back at the electronic versus steric debate, outlined in Section 13.3. However, one must be cautious. In the case of CX4 being inert towards attack by water, the lack of C d orbitals presupposes that the reaction would proceed through a 5-coordinate intermediate (i.e. as is proposed for hydrolysis of silicon halides). Of course, it is impossible to establish the mechanism of a reaction that does not occur Certainly, CF4 and CCI4 are thermodynamically unstable with respect to hydrolysis compare the value of AjG° for equation 13.35 with that of —290 kJ mol for the hydrolysis of SiCl4. 

---