Triangular planar molecular

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. 2.20. Allowed planar molecular orientations in the representation of double (upper row) and ordinary (lower row) azimuthal angles two rigidly fixed molecular orientations (n = 2) for a square lattice (a) and for a triangular lattice (b), and four discrete orientations (n = 4) on a square lattice (c).

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. 

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. 

Three electron pairs, all bonding, yield the same electron-pair and molecular geometries trigonal (triangular) planar (Line 2). Each bond angle is 120°. 

Molecular geometry Tetrahedron tetrahedral Trigonal (triangular) planar Valence shell electron-pair repulsion theory (VSEPR) Section 13.3 Angular Bent... 

For example, in a plane triangular molecule such as BF3, each of the twofold symmetry axes lying in the plane can be carried into coincidence with each of the others by rotations of 27r/3 or 2 x 2nl3, which are symmetry operations. Thus all three twofold axes are said to be equivalent to one another. In a square planar AB4 molecule, there are four twofold axes in the molecular plane. Two of them, C2 and C2, lie along BAB axes, and the other two, C and Ci, bisect BAB angles. Such a molecule also contains four symmetry planes, each of which is perpendicular to the molecular plane and intersects it along one of the twofold axes. Now it is easy to see that C2 may be carried into C2 and vice versa, and that C2 may be carried into C2 and vice versa, by rotations about the fourfold axis and by reflections in the symmetry planes mentioned, but there is no way to carry C2 or C into either CJ or Cn or vice versa. Thus C2 and C2 form one set of equivalent axes, and and C form another. Similarly, two of the symmetry planes are equivalent to each other, but not to either of the other two, which are, however, equivalent to each other. 

The B atom has an incomplete octet in all its trihalides. The compounds consist of planar triangular molecules with an empty 2p-orbital perpendicular to the molecular plane. The empty orbital allows the molecules to act as Lewis acids, which accounts for the catalytic action of BF3 and BC13. 

The VSEPR theory has its roots in the observation prior to 1940 that isoelectronic molecules or polyatomic ions usually adopt the same shape. Thus BF3, B03 C03, COF2 and NO3 are ail isoelectronic, and they all have planar triangular structures. As developed in more recent years, the VSEPR theory rationalises molecular shapes in terms of repulsions between electron pairs, bonding and nonbonding. It is assumed that the reader is familiar with the rudiments of the theory excellent expositions are to be found in most inorganic texts. 

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