Water – the Magic Element
We drink it, we need it to keep ourselves clean and we enjoy swimming in it. More than sixty percent of our body consists of it: water. Nothing is taken for granted like water is. For scientists it is quite a different matter. Nothing is clear. There are a lot of mysteries surrounding water, starting with its chemical composition.
Water is made up of two elements: one of them, oxygen, is the most abundant of all terrestrial elements and the other one, hydrogen is the simplest and the third most common element. In water the ratio of hydrogen to oxygen is 2 : 1. Therefore, water is a small molecule but its qualities are quite unusual.
Chemical Aspects
The water molecule has a very characteristic structure; it does not resemble a ball but looks more like the letter V. The oxygen and the two hydrogen atoms include an angle of 104°. It is the oxygen that attracts the electrons it shares with the two hydrogen atoms; the latter ones receive a partial positive charge, whereas oxygen carries a partial negative charge. This asymmetric charge is the base of the so-called hydrogen bridges the bonding forces of which are something between the normal covalent bond within a molecule and the forces between different molecules, the so-called Van-de-Waal’s forces.
These special hydrogen bridges are primarily important for the very specific qualities of water. They account for the liquid state of water at temperatures between 0° and 100° Celsius. If we compare water to its most similar substances, for example hydrogen sulphide, then it should be gas in this temperature range. In its solid form water is ice which is lighter than water – its liquid form. Hydrogen bridges weave a voluminous net out of the water molecules. That is an important difference compared to other molecules. So ice swims on the surface of water thus allowing fish and other water life to survive the winter. The ice functions as an insulating layer.
Jane Funke und Hannelore Gießen
Diesen Artikel finden Sie in DAS PTA MAGAZIN 06/2007 auf Seite 52 f. oder als PDF-Download im Kasten oben rechts.
