Homoatomic bond

Fig. 3.1 The plot of parameter D vs. parameter N. The plot contains elements (x), cations without homoatomic bonding ( ), anions without homoatomic bonding (O), cations with homoatomic bonding ), anions with homoatomic bonding (O), and ideal structures +). The definitions of some of the ideal structures are as follows, ideal rutile the oxygen positions of the ideal...

Fig. 3.7 Plot of the D parameter of cations (DJ against the D parameter of anions (Da) for selected binary structures. Compounds with homoatomic bonds are excluded.

MOLECULAR STRUCTURE-PROPERTY RELATIONS Table 4.11 Covalent radii (pm) within homoatomic bonds... 

Soluble heptapnicanortricyclane anions [Pny] (Fig. 3a) and trishomocubane-shaped (ufosane-like) anions [Pnn] (Fig. 3d) are very common and known as in the binary solids for Pn = P, As, Sb (Table 2). Oxidative coupling of these monomers leads to the dimers [Pny-Pny]" and [Pnn-Pnn]" for Pn = P and As (Fig. 3b, e), which - as observed for the tetrel element clusters - have an external homoatomic bond, but in this case the structures of the monomeric units are fully retained upon dimerization. A trimeric oxidative coupling product of [Py] is the... 

There are a number of compounds containing homoatomic bonds that fall outside the formal oxidation state III or V classification, e.g., Zintl anions and homoatomic cations of Sb or Bi, but these have little or no coordination chemistry. 

In a homoatomic bond, i.e. one between two atoms that are the same, the electrons in the covalent bond are shared equally between the two nuclei. This means that there is no permanent charge separation, i.e. one end is not permanently positive, nor the other permanently negative. Suggest two homoatomic molecules formed from elements selected from the first two rows of the Periodic Table. 

In a homoatomic bond, such as between two fluorine atoms, there is no permanent charge separation. If the bond in the fluorine molecule should break, what do you think would be the likely products Write an equation for your suggested answer. 

In summary, homolytic cleavage usually occurs with homoatomic bonds, or when the degree of polarisation is small. The result of such a cleavage is two radicals. Heterolytic cleavage occurs when the degree of polarisation is large, or... 

A homoatomic bond exists between identical atoms. In such a case the bond is unpolarised, because the electrons are equally shared, and so there is no permanent charge separation. 

Homoatomic bonds tend to prefer homolytic bond fission, which results in radicals being formed while heteroatomic bonds often undergo heterolytic bond fission, which results in ions being formed. 

This results in one oxygen having two lone pairs, one homoatomic bond and one unpaired electron, which means that it has a share in the six electrons in the valence shell, exactly as it would have had in the elemental state, and so its oxidation number is zero. The other oxygen has three lone pairs and one homoatomic bond. Thus, it has a share in seven electrons, which is one more than the elemental state, and so it has an oxidation state of-1. This analysis resolves the problem of fractional oxidation numbers that was encountered above. 

When a further electron is added to form the peroxide anion, 02, both oxygen atoms have three lone pairs and one homoatomic bond and so each atom now has an oxidation number of-1. 

Secondly, a triply bonded dinitrogen molecule, in which each nitrogen has an oxidation of zero, bonds to the atomic nitrogen anion to give rise to one of the canonical structures of the azide anion, namely, one terminal nitrogen has one lone pair and three homoatomic bonds, and so has an oxidation number of zero. The central atom has four homoatomic bonds, but one of which is polarised away from it, i.e. the dative bond, and so it has an oxidation number of+1. The other terminal nitrogen started with one extra electron and now also has a homoatomic bond, which is polarised towards it, and so now has an oxidation number of-2. This nitrogen atom has three lone pairs. 

The sulphur that occupies a terminal position is in a similar configuration to one of the oxygens. However, it has two covalent homoatomic bonds to the central sulphur and so its oxidation number is zero. The central sulphur has four heteroatomic bonds to oxygen atoms and in each case they are polarised away from the sulphur, and so its oxidation number is +4. Thus, instead of each sulphur being given the same oxidation number of +2, as was the result above, a distinction is drawn between them which reflects the different chemical environments they occupy. 

It should be noted that A is the difference between Da-b and the arithmetic mean of the homoatomic bond energies. 

In some cases it is possible to deduce homoatomic bond energies by extrapolation from the trend of bond energies observed within the periodic table. Figures are given in Table 9. 

Phosphorus is second only to carbon in the structural diversity of its homoatomic bonded forms In addition to monocyclic ring sizes from three to six, many different polycyclic structures have been identified ... 

The inherent basis of these procedures is the Zintl-Klemm concept and the Mooser-Pearson extended (8 — N) rule. Formerly applied only to classical two-center-two-electron bonds, the extended procedures comprise all varieties of bonding (multiple bonds, partial bonds, multicenter systems, radicals, and free electrons). Generally, for a compound AmB , an electron transfer A- A +, B- mp = nq ) to the more electronegative element B forms pseudoelements k, B that show the structural principles of the corresponding isoelectronic elements with the whole spread of homoatomic bond types. Alternatively, one can derive from the number of valence electrons e and cb according to the equation otca + nee + k = 3n the term k = saa + Y. bb - e, which accounts for the... 

Schnering, H.G. von (1981). Homoatomic Bonding of Main Group Elements. Angew.Chem. lnt.Ed.Engl 20, 33 - 51. 

H-G. Von Schnering, Homoatomic bonding of main group elements, AWC, 20, 33, 1981. 

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