Water is a transparent, odorless, tasteless liquid composed of the elements hydrogen and oxygen. Water is an universal solvent, meaning that many elements can be dissolved by water. Fresh water has relatively few elements dissolved in the water, while the oceans contain many dissolved salts.
Water is important to our lives, and without it we could not live. In fact, there are no living creatures that can live without water. Water most probably originated on this planet as gases were emitted from volcanoes. The Earth's atmosphere captured this water and has continuously recycled it throughout time, in what is called the water cycle. Water evaporates and forms clouds – the clouds provide rain and snow – which is collected in rivers, lakes, underground reservoirs, and oceans – that are the source for further evaporation. Water is the perfect substance for the water cycle, because it has a high boiling point and a low freezing point.
|How water molecules "stick" together.|
The molecular structure of water resembles that of a teddy bear’s head. The hydrogen and the oxygen atoms have a very tight covalent bond formed where the hydrogen and the oxygen share electrons. Bonding between molecules of water is called a hydrogen bond, which has a weaker attraction. The hydrogen atoms of one water molecule stick to the oxygen atoms of nearby water molecules. These weak bonds are very important for the chemistry of life. Molecules which stick to water, such as alcohol and sugar, are called hydrophilic, meaning "water loving."
Not all molecules are sticky. The scientific name is hydrophobic which means "water fearing." Examples of slippery molecules are fats and oils.
Water exhibits surface tension. Surface tension of water or the ability of a substance to stick to itself makes water an excellent substance to float heavy objects on its surface. The molecules of water on the surface of a calm and quiet pond tend to be drawn into the liquid, so that the liquid surface is taut, like a sheet of rubber drawn over the open mouth of a jar. This tautness is caused by surface tension.
Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer. The surface of water can support small objects like a sewing needle until the surface tension is broken. This "skin" on the water aids the growth of mayflies and caddisflies that are attached to the water’s surface. However, surface tension can also trap flying insects that accidentally fall into the water and are unable to fly out.
|Capillary action on a wide tube|
Soaps and detergents help the cleaning of clothes by lowering the surface tension of the water. This allows the water to soak into pores and dirty areas more effectively. Small insects such as the water strider can walk on water because their weight is not enough to penetrate the power of surface tension.
Common tent materials are somewhat rainproof because surface tension of water will bridge the pores in the finely woven material. But if you touch the tent material with your finger, you will break the surface tension and the rain will drip through.
Water can defy gravity as it can "walk" up the sides of a thin tube. The molecule is actually attracted to the side and pulls itself up. It might take a long time to get up a thin capillary tube, but it is working against gravity.