Period 2 molecules fluorides

Consider the fluorides of the second-row elements. There is a continuous change in ionic character of the bonds fluorine forms with the elements F, O, N, C, B, Be, and Li. The ionic character increases as the difference in ionization energies increases (see Table 16-11). This ionic character results in an electric dipole in each bond. The molecular dipole will be determined by the sum of the dipoles of all of the bonds, taking into account the geometry of the molecule. Since the properties of the molecule are strongly influenced by the molecular dipole, we shall investigate how it is determined by the molecular architecture and the ionic character of the individual bonds. For this study we shall begin at the left side of the periodic table. 

In this section we discuss the bonding of the fluorides, chlorides, and hydrides of the elements of periods 3 and beyond with LLP coordination numbers up to four with particular emphasis on the elements of period 3. As might be expected these molecules show many similarities to the corresponding period 2 molecules, and the differences can be mainly attributed to the larger size and lower electronegativity of the atoms of a period 3 element compared to the corresponding period 2 element. 

Because of the -dependence of aa, the innermost electron shells make the largest contribution, but the fall-olf is fairly gradual, as we shall see in examples below. For free atoms, aa increases steadily with the number of electrons, as shown in Fig. 2, but the increase is periodic in molecules, as shown in Figs. 6-8 for the binary hydrides and fluorides. 

The type of products depends largely on the reaction temperature (Thomaset al., 81). At the boiling point of the isobutylene (— 6°) polymerization in the presence of boron fluoride yielded an oil after a considerable induction period. On the other hand, if the isobutylene was precooled to — 80° an immediate reaction occurred with almost explosive violence, producing a polymer of a very much higher molecular weight. The molecular weight of the polyisobutylene molecule increased from... 

Some attempts have been made in recent years to establish the identity of the neutral products of ion-molecule reactions. Smith et al. (1980) carried out a flowing afterglow experiment in which neutral products were collected at the end of the flow tube during periods ranging from 15 minutes to 1 hour. Analysis by glc of the collected fractions shows neopentyl fluoride as the only neutral product in reaction (24). 

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