Other Tetrahedral Molecules

5-5 other tetrahedral molecules Members of the carbon family (carbon, silicon, germanium, tin, and lead) readily form four o- bonds with four adjacent atoms. The resulting molecules invariably have a tetrahedral structure around 

Molecule Bond Bond length, A Bond energy (BE), kcal/mole 

A number of important oxyanions have a tetrahedral structure, among them and C104. Properties of a representative group of tetrahedral molecules are given in Table 5-1. 

Describe the bonding in CF4 in terms of molecular orbitals, and construct a molecular-orbital energy-level diagram. Around which nucleus or nuclei do the electrons spend more time in the 7 orbitals Do you expect any partial ionic character in the C—bonds What is the dipole moment of CF4 Why  

Under what conditions are the molecular-orbital and valence-bond descriptions of bonding in CH4 the same From Eqs. C5-1), (5-3), (5-5), and (5 7), construct the valence-bond bonding functions that are shown in Fig. 5-8. 

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The hydrogen group orbitals are referred to as symmetry adjusted linear combinations (SALC). Although their development will not be shown here, the molecular orbital diagrams for other tetrahedral molecules are similar. 

Pb(CD3)4 are 726xl0 and 569 x 10 cm respectively [47]. For centrifugal distortion constants, see [49]. The rotational branch structure to the skeletal fundamentals is studied and OR, RS branch separations are observed and compared with calculated values [35]. The PR separations are 15.7 and 13.9 cm respectively [47]. The inertia defect, bringing out the influence of vibration-rotation interaction on molecule structure was calculated and compared with that of other tetrahedral molecules [48]. 

All these compounds have (distorted) tetrahedral molecules, those of formula O2SX2 having C2v symmetry and the others Cj. Dimensions are in Table 15.15 the remarkably short O-S and S-F distances in O2SF2 should be noted (cf. above). Indeed, the implied strength of bonding in this molecule is reflected by the fact that it can be made by reacting the normally extremely inert compound SFg (p. 687) with the fluoro-acceptor SO3 ... 

The most interesting oxides of Ru and Os, however, are the volatile, yellow tetroxides, RUO4 (mp 25°C, bp 130°C< 3>) and OSO4 (mp 40°C, bp 130°C). They are tetrahedral molecules and the latter is perhaps the best-known compound of osmium. It is produced by aerial oxidation of the heated metal or by oxidizing other compounds of osmium with... 

Like the carbon atom in methane and the nitrogen atom in methylamine, the oxygen atom in methanol (methyl alcohol) and many other organic molecules can also be described as sp3-hybridized. The C-O-H bond angle in methanol is 108.5°, very close to the 109.5° tetrahedral angle. Two of the four sp3 hybrid... 

White phosphorus is composed of tetrahedral molecules of P4 in which each P atom is connected to three other P atoms. Draw the Lewis structure for this molecule. Does it obey the octet rule ... 

Diamondoids, when in the solid state, melt at much higher temperatures than other hydrocarbon molecules with the same number of carbon atoms in their structures. Since they also possess low strain energy, they are more stable and stiff, resembling diamond in a broad sense. They contain dense, three-dimensional networks of covalent bonds, formed chiefly from first and second row atoms with a valence of three or more. Many of the diamondoids possess structures rich in tetrahedrally coordinated carbon. They are materials with superior strength-to-weight ratio. 

Zig-zag chains are also obtained starting from many other neutral tectons wherein the donor and/or acceptor sites have an angled geometry, e.g. (Z)-diazaalkenes [171]2, phosphine oxides [79], carbonyl [150], phosphoramidyl [124,139], and sulfinyl [151] sites, tetrahedral molecules that work as bidentate modules (e.g. the adducts CBr4/DABCO [172],... 

The bond pointing "up" constitutes one C-H bond in that direction while the other three must exactly equal the effect of one C-H pointing "down." The "down" component of each of the three bonds can be obtained from cos(180 — 109° 28 ) = 1/3. Therefore, the three bonds exactly equal the effect of the one bond pointing in the "up" direction. This would be true for any regular tetrahedral molecule, so the dipole moment would be zero. 

A simple, previously mentioned example may be represented by the tetrahedral molecule P4. In this structure there are 4 vertex atoms (n = 4) and there are no exocyclic groups. On the other hand, P has 5 valence electrons, so the number of cluster electrons is 4 X 5 = 20 electrons. This number (20) is therefore related to the number of vertices by the condition 20 = 5n. The cluster is electron-precise. 

If equal bond dipoles act in opposite directions in three-dimensional space, they counteract each other. A molecule with identical polar bonds that point in opposite directions is not polar. Figure 1.5 shows two examples, carbon dioxide and carbon tetrachloride. Carbon dioxide, CO2, has two polar C=0 bonds acting in opposite directions, so the molecule is non-polar. Carbon tetrachloride, CCI4, has four polar C—Cl bonds in a tetrahedral shape. You can prove mathematically that four identical dipoles, pointing toward the vertices of a tetrahedron, counteract each other exactly. (Note that this mathematical proof only applies if all four bonds are identical.) Therefore, carbon tetrachloride is also non-polar. 

Here a designates the trace of the polarizability tensor of one molecule (l/47i o) times the factor of a represents the electric fieldstrength of the quadrupole moment q2. Other non-vanishing multipole moments, for example, octopoles (e.g., of tetrahedral molecules), hexadecapoles (of linear molecules), etc., will similarly interact with the trace or anisotropy of the polarizability of the collisional partner and give rise to further multipole-induced dipole components. 

In other words, for tetrahedral molecules, these relationships differ from the ones used for the linear molecules, especially Eq. 4.18. As a consequence, we must rederive the relationships for the spectral line shape and spectral moments. If the intermolecular interaction potential may be assumed to be isotropic, the line shape function Vg(a> T), Eq. 6.49, which appears in the expression for the absorption coefficient a, Eq. 6.50, may still be written as a superposition of individual profiles,... 

A water molecule hydrogen bonded to four other water molecules note the tetrahedral arrangement of bonds around the central oxygen. 

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