Valence shell atomic orbitals oxygen

Figure 6, Electron-density plots for the valence-shell atomic orbitals of sulfur, oxygen, and hydrogen as the free atoms. These plots are to the same scale as those given in Figures 2 through 5 and 7 through 10.

The electrons which are important for the bonding in the water molecule are those in the valence shell of the oxygen atom 2s22p4. It is essential to explore the character of the 2s and 2p orbitals, and this is done by deciding how each orbital transforms with respect to the operations associated with each of the symmetry elements possessed by the water molecule. 

Figure 8. Electron-density plots of the valence-shell molecular orbitals of the H2SO molecule in the plane containing the oxygen and the sulfur atoms, the plane which bisects the H-S-H angle...

Although the number of protons around the oxygen atom may vary, the nnmber of electrons and the electron orbitals remain essentially the same. The valence shell of the oxygen atom is short of two electrons for a complete shell and the hydrogen atoms have one electron each. The latter two electrons are donated to fill the oxygen valence shell. The bonding scheme is quite simple, with four lone-pair electrons and two electrons in each bond (Figure 3.2). 

In writing these configurations for diatomic molecules of second-row elements, we have omitted the electrons from the Is orbitals because they are not part of the valence shells of the atoms. When considering the oxygen molecule, for which the a orbital arising from the combinations of the 2pz orbitals lies lower in energy than the 7r orbitals, we find that the electron configuration is... 

Phosphorus is directly below nitrogen in the periodic table. (The relationship of the chemistry of phosphorus to that of nitrogen is somewhat like the sulfur-oxygen relationship discussed in the introduction to Chapter 17.) The phosphorus atom electron configuration is Ne 3.s,23/J3, and it has five outer-shell electrons, as shown by its Lewis symbol in Figure 18.1. Because of the availability of underlying 3d orbitals, the valence shell of phosphorus can be expanded to more than eight electrons. 

Unhybridized oxygen 2/ -orbitals would form two OH bonds 90° apart. According to the valence-shell model, the two bonds would belong to distorted tetrahedra around each oxygen atom. 

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