Effects of Radicals - Unpaired Electron

We must know look at the way in which the atoms of water are bonded together. Remember that water consists of a single atom of oxygen with two hydrogen atoms linked on to it. The bonds between the oxygen atom and each hydrogen atom consists of a pair of electrons shared between the atoms one from the hydrogen atom and one from the oxygen atom. The water molecule, however, routinely separates into two particles called ions that wander about freely. The term 'ion' just means 'wanderer'.

One of these two ions of water is a hydrogen atom (H) without its electron. Bearing in mind that the nucleus of an atom is positively charged and that electrons are negative, you will see that this ion is positively charged. The other ion is a complete hydrogen atom, with its electron, linked to a complete oxygen atom but with the electron missing from the first hydrogen atom also stuck on (OH). So this ion is negatively charged. The H ion is called a 'positive ion', and the OH ion is called a 'negative ion'. This is the normal way for water to be split up and is known as 'ionization'. Positive and negative ions are important in chemistry, and many chemical reactions occur between different ions coming together.

About 50 years ago it was discovered to the astonishment of the chemists that, under certain circumstances, the water molecule can split up in another, quite different, way. If ,for instance, water is exposed to radiation such as X-rays or gamma rays, the two electron bonds between the oxygen and the hydrogen atoms can briefly split, leaving one electron on the hydrogen and one on the oxygen atom combination the hydroxyl radical thus creating two radicals, both electrically neutral but both having only one spare electron. Thus momentarily, we have two atoms each with only one electron in an outer orbital. Both the hydrogen radical and the hydroxyl radical are horribly active. It is the unpaired electron that makes them so chemically active. A group with an unpaired electron is highly unstable and is desperate either to pick up another electron from somewhere, or to give up its solitary electron. The hydroxyl radical is the most reactive free radical known to chemistry and will attack almost every molecule in the body. 

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