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MIRACULOUS WATER
The three fourth parts of the human body are formed by water, which indicates the importance that this miraculous compound has for life. If we consider that a person can lose an average of about three liters of water each day, we could be aware of the necessity to maintain and to regulate that liquid level indispensable for our life, to such an extent that we can get to stay three weeks without eating but not more than nine or ten days without drinking.
But why is the water something so indispensable and necessary? Could not another compound or substance make the same functions that the water? We are going to stop in order to analyze the properties of the water, and we will realize that is a peculiar substance.
There is a general tendency of all chemical compounds to have a higher boiling point as much as its molecular weight is increasing. The water boils to 100º C, so if we compare it with a substance that also has a boiling point next to that temperature, like Cl 2 O 7 with an atomic weight of 183, we should suppose that around this number it would be the atomic weight of water. However, this is not truth since water has a value of 18, it means, ten times smaller than we had waited. First surprise!.
The water is formed by molecules, that they are formed as well by three small atoms, two of hydrogen (H) and one of oxygen. Oxygen (O) is the first member of a family of elements that also includes sulphur (S), the selenium (Se) and tellurium (Te). Each atom of these elements can form molecule with two hydrogen atoms of such form:
If we pay attention to the progression of the boiling point for each compound based on its molecular weight we can observe that for the water would be possible to obtain a boiling point of - 73º C, however, water boils to 100º C behaving of an anomalous form to the rest of composed. We can thank to this anomaly, since if this didn't happen, the water would exist only in our planet like steam, so the life in the planet would be very difficult.
So, why water is so especial? The answer is that oxygen is a very electronegative element like fluorine or nitrogen, which it means; they have a noticeable tendency to monopolize electrons with negative load. In the case of water, each hydrogen atom shares an electron with oxygen, but due to the high tendency of oxygen to capture these electrons, these ones are more near the oxygen atom than hydrogen ones, so hydrogen takes a certain positive charge and oxygen the negative one. This type of molecules is denominated, therefore, polar molecules, since they have poles in which the electrical charges are concentrated. The result of these poles is the forces of attraction and repulsion between water molecules. Negatively charged Oxygen of a molecule forms small connections with positively charged hydrogen of other molecules. Due to this special force between molecules it is necessary to apply more energy than we had expected in order to separate them and to produce the boiling, so, instead of boiling to - 73º C water does to 100º C as we know, so thanks to this peculiar connection called 'hydrogen connection', life on the Earth is possible.
Because of this connection, if we want to increase a degree the temperature of the water, we must contribute a quite high heat to be able to separate these forces, in such form that when they form these small connections again they will give off that additional heat. It is said that water has a great caloric capacity. Due to it, the temperature of the sea and the rivers won't change very much with climatic changes, which allow to the aquatic organisms to live.
In addition, the sea will act like thermal regulator, absorbing the heat of the sun in summer or giving off heat in winter. In order to verify this, it is not necessary more to compare the temperatures of regions next to the sea with other farther.
It means the amount of heat necessary for fusing the ice or for making boil the water is higher than we had waited, since it is necessary to break these connections between molecules. Of course, this amount is also given off when we congeal the water or we condense the water steam.
Another important property of water is its power to dissolve substances. This is due to the polar form of the molecule that allows an ionic molecule can dissociate of such form that their ions move freely. This also happens in other polar compounds that also have concentrations of separate-loading charges, being also able to dissolve in the water. On the other hand, it cannot dissolve no polar substances like hydrocarbons, fats etc. The consequence of all this is also more important for life.
The most important substances of the human body are polar molecules, what it allows to dissolve them in the water. In addition to that, ionic gradients in a cellular scope based on the concentration of certain salts in the water are settled down. This is the base of much biological process. Thanks to water and its dissolvent powerful, substances by the organism can be transported.
But in case they were few all these strangers and anomalous properties, still we need to comment the strange behaviour of the water density. In a normal way, when we diminish the temperature of a substance, what we do is to reduce the vibratory energy of its molecules, so they will be more compressed and they will increase the density. However, this general norm to increase the density when we diminish the temperature seems that it does not say with the water. To 100 degrees, the liquid water reaches its minimum density (0.958 g/cm 3 ), if we low the temperature its density increases, so it behaves like the rest of the substances known in the nature. However, when it arrives at 4º C the density already reaches a value of 1.000 g/cm 3 and if we continue lowing the water begins to expand, opposite that we had expected, it diminishes its density until 0.999 g/cm 3 to 0º C. This strange phenomenon does not finish here, since if we carry on cooling until we congeal the water, this one will diminish the density abruptly having a value of 0.92 g/cm 3 to 0º C. This peculiar phenomenon is vital for the life in our planet and it must be analyzed with thoroughness, but that, it will be another chapter.
