Free Radicals
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Free Radicals

Sometimes we have to deal with atoms or molecules that don't have all of their electrons paired up or bonded. We call these free radicals.

One example is the chlorine free radical that has been implicated in the destruction of ozone in the upper atmosphere.

: Cl :
Another example is the hydroxyl free radical that can result when water molecules are broken apart by radiation or other reactions. This happens in our bodies often enough that we have certain enzymes dedicated to reacting with hydroxyl free radicals.

: O :

A third is nitrogen dioxide, one of the components in smog. A variety of Lewis diagrams can be drawn for this one, but they all seem to end up with one unpaired, unbonded electron.               
: O : N : : O


In each of these examples it is the unpaired, unbonded electron that makes these free radicals so reactive. These atoms and molecules have room for and a strong attraction for an additional electron. They can react with a wide variety of other chemicals to gain electrons.


Practice Identifying Free Radicals

To give you just a little practice working with free radicals, take some time now to identify the free radical in each of the following pairs of chemicals. Also, draw a Lewis diagram that illustrates why that chemical is a free radical. (This is also given in exercise 23 in your workbook.) Answers follow on the next page.

CO or NO
chlorine atom or chlorine molecule




N : : O
chlorine atom
: Cl :


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