Triangular-planar molecules

The triangular planar (D3h symmetry) CO/ molecular ion with 24 electrons (AB324-type) in CaC03 is easily ionized by radiation to electron and hole centres self-trapped in the lattice or an oxygen vacancy type C02 molecular ion at the anon site. Molecular orbital schemes based on the general scheme of AB3 molecules with 25,24 and 23 electrons for atoms A (B, C, Si, N, P, As and S) and B (O) characterize their specific -factor. Hence, the anisotropic -factor of these radicals estimated from the powder spectrum has been to identify the radical species.1... 

In any molecule in which there are no nonbonding pairs around the central atom, the molecular shape is the same as the molecular geometry. Thus, to use the examples from Table 6.2, all three two-substituent molecules have both a linear geometry and a linear shape. Both BH3 and H2CO have a triangular planar shape, CH4 has a tetrahedral shape, PF5 a triangular bipyramidal shape, and SF6 a square bipyramidal shape. 

If ammonia, NH3, were somehow squashed into a triangular planar shape, the molecule would gain in symmetry and become less polar. Of course, the ammonia would no longer be identifiable as ammonia because its physical and chemical properties would become vastly different. 

Write electron-pair structures for each of the following. Include both bonding and nonbonding pairs and predict the preferred shape of the molecule or ion. as linear, triangular (planar), angular, tetrahedral, or pyramidal. 

At normal temperatures, sulfur trioxide is a volatile liquid (its boiling point is 45°C), composed of triangular planar S03 molecules. In the solid, and to some extent in the liquid, these molecules form trimers (unions of three molecules) of composition S309 (14) as well as larger combinations. 

In an atom, the hybridization of s and p orbitals to form sp orbitals provides electron probability areas where bonds can form to make a molecule more stable than if the bonding had occurred in the individual s and p orbitals. The sp orbitals have one large lobe and one small lobe and are aligned along x, y, and z coordinates so that four sp orbitals, called sp3 orbitals because they are made of one s and three p orbitals, result in a tetrahedral-shaped arrangement. When there are three sp orbitals, made of one s and two p orbitals, called sp orbitals, the molecular has a triangular-planar shape. If there is bonding in two sp orbitals, made of one s and one p orbital, a linear molecule results. 

Explain why some four-atom molecules, such as NH3 (ammonia), have a pyramid shape, and other four-atom molecules, such as A1C13 (aluminum chloride), have a triangular-planar shape. 

The observed geometry of the molecule is in accord with the predicted orientation of the hybrid orbitals the sp AO s are planar and separated by 120° (Fig. 19.3). This is also the arrangement that permits the maximum bond angle (minimum electron repulsion). The sp hybrid AO s always have this triangular, planar orientation and hence are called TRIGONAL hybrid orbitals. 

Fig. 19.22. Vector representation of zero dipole moments for (a) linear, AB2 b) triangular planar, AB3 and (c) tetrahedral, AB4 molecules. The dashed arrows are resultant vectors.

Norbornadiene (NBD) forms two different complexes with silver nitrate, NBD-AgN03 18,19) and NBD-2AgN03 (/, 18,19). The latter complex, for which a crystal structure has recently been reported (2), can be obtained by adding N BD to an aqueous solution of silver nitrate. The crystals that separated were recrystallized from ethanol. Each double bond in the norbornadiene molecule is coordinated to a silver atom in a triangular-planar configuration. The NBD molecule then serves to cross-link two AgN03 chains. 

The molecular orbital structure of a portion of a trans polyacetylene molecule (Figure 9.1) is shown in Figure 9.2. The carbon atom bonding is hybridized as was discussed for semiconductors in Chapters 2 and 5, with s-l-px+Py atomic orbitals (Figure 9.2b) forming the sp triangular planar molecular orbital structure and... 

Fig. 2.16. Planar orientational structures of nonpolar molecules on a triangular lattice.

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