Molecular shape linear structure

Can Lewis structures provide us with information regarding the actual spatial arrangements of atoms within molecules To explore this question, let us invent a triatomic molecule and call it XY2, in which X is the central atom with bonds to each Y atom. Each bond is polar since the joined atoms have different electronegativities. Therefore each bond contributes to the overall dipole moment of the molecule. Consider two possibilities for the molecular shape, linear and bent ... 

The secondary structure describes the molecular shape or conformation of the polymer chain. For most linear polymers this shape approaches a helical or pleated skirt (or sheet) arrangement depending on the nature of the polymer, treatment, and function. Examples of secondary structures appear in Figure 2.13. 

Organic polymers are responsible for the very life—both plant and animal—that exists. Their complexity allows for the variety that is necessary for life to occur, reproduce, and adapt. Structures of largely linear natural and synthetic polymers can be divided into primary structures, which are used to describe the particular sequence of (approximate) repeat units secondary structures, which are used to describe the molecular shape or conformation of the polymer tertiary structures, which describe the shaping or folding of macromolecules and quaternary structures, which give the overall shape to groups of tertiary-structured macromolecules. The two basic secondary structures are the helix and the sheet. 

Non-linear group contribution with extensive structural corrections which account for effects related to molecular shape and polar effects. 

S2.3 The Lewis structures and molecular shapes for XcFi and ICb are shown below. The XeFi Lewis structure has an octet for the 4 F atoms and an expanded valence shell of 10 electrons for the Xe atom, with the 8 + (2 x 7) = 22 valence electrons provided by the three atoms. The five electron pairs around the central Xe atom will anange themselves at the comers of a trigonal bipyramid (as in PF5). The three lone pairs will be in the equatorial plane, to minimize lone pair-lone pair repulsions. The resulting shape of the molecule, shown at the right, is linear (i.e., the F-Xe-F bond angle is 180°). 

In fig. 5 we see that, indeed, the T-shaped and the staggered parallel structure have maximum electrostatic attraction. The dispersion energy is most favourable, of course, for the linear structure. For distances in the neighbourhood of the (isotropic) Van der Waals minimum the (short range) exchange repulsion is the dominant anisotropic term, however. Since it increases very steeply when the molecular charge clouds start to overlap (especially in the linear structure 0 = 0g = 4>a — 1... 

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