Oxygen diatomic, electronic structure

Kotani, M., Mizuno, Y., Kayama, K., and Ishiguro, E., J. Phys. Soc. Japan 12, 707, Electronic structure of simple diatomic homonuclear molecules. I. Oxygen molecule. ... 

Ordinary oxygen consists of diatomic molecules with an unusual electronic structure. We might expect these molecules to contain a double bond ... 

This proposed electronic structure for diatomic oxygen contains a double bond between the two atoms, which on the face of it, would suggest that the molecule ought to be quite unreactive. In fact, diatomic oxygen is quite reactive. Suggest a reason for this. 

Chapters 1 and 2 dealt primarily with the electronic structure of isolated atoms of the various elements. With the exception of the noble gases, however, it is the molecule, not the individual atom, that is the basic building block of materials in nature. Even elements that occur naturally in their pure state are generally found in molecular form. For example, the oxygen and nitrogen in the atmosphere are made up of the diatomic molecules O2 and N2, not discrete O and N atoms. In Chapter 3, we begin our study of molecules and the chemical bonds that hold them together. 

The increased-valence theory represents a natural extension of the more familiar Lewis-Pauling valence-bond theory. Therefore an understanding of it may be useful for all chemists who have an interest in qualitative valence-bond descriptions of electronic structure. It will be shown that all Lewis-type valence-bond structures with lone-pairs of electrons can be stabilized easily via one-electron delocalizations from doubly-occupied atomic orbitals into diatomic bonding molecular orbitals when the relevant atomic orbitals overlap, as is shown here for the two sets of oxygen n electrons of N2O. 

The behavior of the / electrons of lanthanides is not fiilly understood, even for the diatomics. The oxides and fluorides are considered to have the simplest electronic structure of the diatomics, because of the strong electronegativity of the oxygen and fluorine atoms. We have analyzed the electronic structure of the ground state and excited states of cerium... 

Linnett used the concept that an octet of valence shell electrons consists of two sets of four opposite-spin electrons to show that in diatomic and other linear molecules the two tetrahedra are not in general formed into four pairs as we have discussed for F2 and the CC triple bond in C2H2. This idea is the basis of the double-quartet model, which Linnett applied to describe the bonding in a variety of molecules. It is particularly useful for the description of the bonding in radicals, including in particular the oxygen molecule, which has two unpaired electrons and is therefore paramagnetic This unusual property is not explained by the Lewis structure... 

Calculated geometries for a small number of diatomic and small polyatomic free radicals are compared with experimental structures in Table 5-18. These have been drawn from a somewhat larger collection provided in Appendix A5 (Tables A5-50 to A5-57). Except for triplet oxygen, all radicals possess a single unpaired electron (they are doublets). The usual set of theoretical models has been examined. All calculations involve use of the unrestricted open-shell SCF approach, where electrons of different spin occupy different orbitals, as opposed to the restricted open-shell SCF approach, where paired electrons are confined to the same orbital (see Chapter 2 for more detailed discussion). 

The properties of oxygen are of course directly related to its molecular structure. The diatomic oxygen molecule is a diradical. A radical is an atom or group of atoms that contains one or more unpaired electrons. Dioxygen is a diradical because it possesses two unpaired electrons. For this and other reasons, when it reacts, dioxygen can accept only 1 electron at a time. 

When sulfur is quenched at reduced pressure from the temperature at which the vapor species is predominantly diatomic S2 to liquid nitrogen temperature, a diatomic solid-state modification is formed with a structure similar to that of oxygen, being paramagnetic with two unpaired electrons, and this structure can be retained up to —80°C (13, 14, 15, 16, 17),... 

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