Bonds bent single

Fig. 4-8.—A representation of the ethylene molecule with the double bond shown as two bent single bonds.

The main result that emerges from the discussions of particular eases is that it has proved possible to give a description of a molecule in terms of equivalent orbitals which are approximately localised, but which can be-transformed into delocalised molecular orbitals without any change in the value of the total wave function. The equivalent orbitals are closely associated with the interpretation of a chemical bond in the theory, for, in a saturated molecule, the equivalent orbitals are mainly localised about two atoms, or correspond to lone-pair electrons. Double and triple bonds in molecules such as ethylene and acetylene are represented as bent single bonds, although the rather less localised o-n description is equally valid. 

It is found that multiple bonds are often formed by elements in the first row of the periodic table (boron, carbon, nitrogen, oxygen), and less often by the heavier elements. For example, the nitrogen molecule, N.>, has the structure N=N , whereas the phosphorus molecule, P4, contains six bent single bonds. 

Figure 11.10 Lewis structures of water (H20). (a) shows two possible configurations of water, but only H-O-H satisfies the electronic requirements of the oxygen atom, (b) shows three possible bond distributions for this structure, but only one (with a single bond to each of the hydrogens and two lone pairs on the oxygen) meets the requirements of all three atoms, (c) shows the bent structure of H-O-H which follows from the need to separate the two lone pairs and two single bonds as far as possible in the three-dimensional molecule, (d) shows a space-filling version of this arrangement, where the oxygen is black and the two hydrogens white.

An oxygen atom also has two pairs of non-bonding electrons, called lone pairs. Since there are a total of four electron pairs around a single-bonded oxygen atom, the shape around this oxygen atom is a variation of the tetrahedral shape. Because there are only two bonds, however, the shape around a single-bonded oxygen atom is usually referred to as bent. 

---