Water (H2O): A Life Sustaining Molecule

Every life form on earth began in water, no life exists without it:

1. Our histology & physiology as an evidence.

When animal moved from the sea to dry land, it took millions of years of evolution, the sea "came with them", even now  millions of years later our body liquid still resembles sea water, we started life in a bag of water at the same temperature as our mother's body, the bag eventually bursts and we are born and new life it breathed into us and suddenly we are a real person relying on air to survive leaving water to take second place, but none the less vitally important as it still makes up over 70% of our body, so for an average healthy adult that sums up to about forty plus litres.

Three litres of our water circulates in our blood with another nine litres exchanging freely with it that are distributed throughout our body tissues but remain outside of them, this twelve litres resembles the "sea that came with us" 

Two litres of water pass into our reservoir every day, and an equal amount passes out as urine and perspiration, this exchange brings in our food, vitamins and mineral requirements and also flushes toxins from the body, controlled carefully by the kidneys and our hormone system to keep (hopefully) our body cells in top condition.

These cells contain the remaining 30 litres of body fluid.

 

The Miraculous Properties of Water:

Water has many exceptional chemical properties. Every water molecule forms by the combination of hydrogen and oxygen atoms. It is quite interesting that these two gases, one combustive and the other combustible, combine to form a liquid, and most interestingly, water.
 
1. The water molecule: the hydrogen bonds.
 
Now, let us briefly see how water is formed chemically. The electrical charge of water is zero, that is, it is neutral. Yet, due to the sizes of the oxygen and hydrogen atoms, the oxygen component of the water molecule has a slightly negative charge and its hydrogen component has a slightly positive charge. When more than one water molecule come together, positive and negative charges attract each other to form a very special bond called "the hydrogen bond". The hydrogen bond is a very weak bond and it is incomprehensibly short-lived. The duration of a hydrogen bond is approximately one hundred billionth of a second. But as soon as a bond breaks, another one forms. Thus, water molecules adhere tightly to each other while also retaining their liquid form because they are combined with a weak bond. 

2. High thermal energy: the hydrogen bonds.
 

Hydrogen bonds also enable water to resist temperature changes. Even if air temperature increases suddenly, water temperature increases slowly and, similarly, if air temperature falls suddenly, water temperature drops slowly. Large temperature changes are needed to cause considerable changes in water temperature. The significantly high thermal energy of water has major benefits for life. To give a simple example, there is a great amount of water in our bodies. If water adapted to the sudden vicissitudes of temperature in the air at the same rate, we would suddenly develop fevers or freeze.  
By the same token, water needs a huge thermal energy to evaporate. Since water uses up a great deal of thermal energy while evaporating, its temperature drops. To give an example, again from the human body, the normal temperature of the body is 36º C and the highest body temperature we can tolerate is 42º C. This 6º C interval is indeed very small and even working under the sun for a few hours can increase body temperature by that amount. Yet, our bodies spend a great amount of thermal energy through sweating, that is, by causing the water it contains to evaporate, which in turn causes body temperature to drop. If our bodies did not have such an automatic mechanism, working for even a few hours under the sun could be fatal.

3. A more viscous liquid: the hydrogen bonds.
 
Hydrogen bonds equip water with yet another extraordinary property, which is water's being more viscous in its liquid state than in its solid state. As a matter of fact, most substances on earth are more viscous in their solid states than in their liquid states. Contrary to other substances, however, water expands as it freezes. This is because hydrogen bonds prevent water molecules from bonding to each other too tightly, and thus many gaps are left in between them. Hydrogen bonds are broken down when water is in liquid state, which causes oxygen atoms to come closer to each other and form a more viscous structure.

An Interesting Property of Water:

1. An unique oxygen hydride.

We all know that water boils at 100º C and freezes at 0º C. In fact, under normal circumstances, water should be boiling not at 100º C but at + 180º C. Why? 
In the periodic table, the properties of elements in the same group vary in a progressive form from light elements towards heavy elements. This order is most evident in hydrogen compounds. The compounds of the elements sharing the same group with oxygen in the periodic table are called "hydrides". In fact, water is "oxygen hydride". Hydrides of other elements in this group have the same molecular structure as the water molecule.
The boiling points of these compounds vary in a progressive way from sulphur to heavier ones; however, the boiling point of water unexpectedly goes against this pattern. Water (oxygen hydride) boils at 80º C less than it is supposed to. Another surprising situation has to do with the freezing point of water. Again, according to the order in the periodic system, water is supposed to freeze at - 100º C. Yet, water breaks this rule and freezes at 0º C, 100º C above the temperature at which it is due. This brings to mind the question as to why no other hydride, but only water (oxygen hydride) disobeys the rules of the periodic system.