Bent triatomic molecules ozone

Fi9Ure 18.3 In addition to translational motion, molecules exhibit both vibrations, in which the atoms positions relative to one another change, and rotations, in which the molecule rotates about its center of mass, (a) A diatomic molecule such as fluorine only exhibits one type of vibration. A bent, triatomic molecule such as ozone exhibits three types of vibration, (b) A diatomic molecule exhibits two (hffeient rotations, whereas a bent, triatomic molecule exhibits three different rotations. (Note that rotation of F2 about the x axis would cause no change in the positions of either atom in the molecule.)... 

Ozone, O3, an allotropic form of oxygen, is a bent triatomic molecule. 

A similar situation arises in the ir-v excited states of ethylene and acetylene where the n interactions become antibonding the excited states are consequently twisted (11) and bent (12) respectively. Another example is provided by triatomic molecules formed by second row atoms ifthe total number of valence electrons exceeds 16, the molecules are bent 33) since there are now antibonding electrons present and bending reduces the resulting unfavourable 7r interaction by replacing p AOs by hybrid AOs (cf. ozone, 13). 

This simple MO pictnre for ozone can also be employed to describe the bonding in other bent triatomic molecnles of second-row elements, such as NO2. Example 4.7 applies molecular orbital theory to CO2, a linear second-row triatomic molecule. 

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