Oxygen—ozone screen

We will look at the importance of the oxygen-ozone screen as a mechanism for protecting us from dangerous UV radiation in Chapter 7. 

The Chapman cycle is a series of chemical reactions related to the oxygen-ozone screening... 

When writing a Lewis structure we restrict a molecule s electrons to certain well defined locations either linking two atoms by a covalent bond or as unshared electrons on a sm gle atom Sometimes more than one Lewis structure can be written for a molecule espe cially those that contain multiple bonds An example often cited m introductory chem istry courses is ozone (O3) Ozone occurs naturally m large quantities m the upper atmosphere where it screens the surface of the earth from much of the sun s ultraviolet rays Were it not for this ozone layer most forms of surface life on earth would be dam aged or even destroyed by the rays of the sun The following Lewis structure for ozone satisfies fhe ocfef rule all fhree oxygens have eighf elecfrons m fheir valence shell... 

Ozone exists naturally in the upper atmosphere of the earth. The ozone layer is especially important because it absorbs ultraviolet light and thus acts as a screen to prevent this radiation, which can cause skin cancer, from penetrating to the earth s surface. When an ozone molecule absorbs this energy, it splits into an oxygen molecule and an oxygen atom ... 

Ozone is formed in the stratosphere by the short-wavelength (< 240-nm) homolysis of molecular oxygen (O2) to two oxygen atoms (O), followed by the subsequent collision of an oxygen atom with an oxygen molecule to produce O3. The absorption spectrum of ozone (X ax = 255 nm) is such that virtually all the potentially damaging ultraviolet wavelengths between 200 and 300 nm are screened out before they reach... 

Ultraviolet radiation has wavelengths in the 200-400 nm range. This energy is sufficient to break some chemical bonds and to create havoc with many biological systems. Fortunately for us, much of the UV radiation that streams from the Sun towards Earth never reaches Earth. It is absorbed primarily by two important screening molecules, oxygen and ozone. Let s examine how this happens. 

Ozone layer Layer in the stratosphere between 15 and 30 km above the earth s surface in which ozone is relatively concentrated (amounts greater than 10 molecules/cm ). The ozone is produced by the action of solar ultraviolet radiation on oxygen and is important in screening the earth s surface from potentially harmful short-wavelength radiation. 

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