Water is an extraordinary substance and shows abnormal behavior from many points of view. In 2003 Martin Chaplin created a site that constantly updates where he describes more than 70 anomalous water behaviors subdividing them into phase, density, material, thermodynamic, physical anomalies (1).
The small size of the water molecule, its lightness, the high difference in electronegativity of its constituent atoms and the asymmetric angle between the oxygen atom and the two hydrogen atoms explain almost all the anomalous behavior of the water. The apparent simplicity of the water molecule does not seem to justify the incredible ability to favor structures and interactions at a much more articulate level of organization of the molecular matter.
The water molecule consists of an oxygen and two hydrogen atoms. The distance between each hydrogen atom and the oxygen atom is on average 0.9585 Ängström and the two hydrogen atoms form with the oxygen atom an average angle of 104.45 °. I say average values because in the molecule in reality there are various kinds of oscillations (removal / approach of the atoms of hydrogen to that of oxygen, variation of the angle between the oxygen atom and the two of hydrogen, torsions in the three directions of space) they make constantly changing angles and distances. In order to better frame the problem, the average oxygen atom diameter is about 1.2 Ängström and that of hydrogen is about 1.06 Ängström (1 Ängström is equal to one ten millionth of a millimeter and a ten thousandth of micron).
The atoms constituting the water molecule pool two pairs of electrons to form a dipole molecule (because the attraction exerted by oxygen is greater than that exerted by hydrogen). This dipolarity makes electropositive hydrogen and electronegative oxygen allowing the existence of a covalent bond at a stable angle (asymmetrical and oscillating around 104.45 °). Moreover this dipolarity makes possible the bond (called hydrogen bridge bond) between hydrogen atoms of a molecule and oxygen atoms of adjacent molecules. Being a dipole of quite large dimensions, the water molecule can be influenced by external electromagnetic fields. Many anomalies of water are attributable to these characteristics, especially to the hydrogen bonds that are formed and destroy continuously.
It would be too long to describe in detail each anomalous behavior of water and explain the chemical and physical reasons for this behavior, for which we mention only some of them referring to Martin Chaplin for further information.
Water has unique moisturizing properties towards important biological macromolecules (in particular proteins and nucleic acids) that determine in solution their three-dimensional structures, and therefore their biological functions. This hydration forms gels that can undergo reversibly the gel-sol phase transitions that underlie many cellular mechanisms.
Substances such as hydrocarbons and fats, being non-polar, are not very soluble or insoluble (hydrophobic substances) while others (proteins, polysaccharides, DNA indispensable for cell functioning) are very soluble (hydrophilic).
The high breaking speed / continuous reconstitution of the hydrogen bonds makes the water less viscous.
The high dielectric constant allows water to easily interact with electromagnetic fields and easily solubilize ionic or very polar compounds.
Due to the small dimensions that allow water molecules to come between one ion and another or between one molecule and another, it is one of the best solvents. To give just one example, the lattice constant of a sodium chloride crystal is equal to 0.564 nanometers (five ten millionths of a meter = five ten thousandths of a micron); this means that the water molecule being five times smaller, can easily enter the crystalline lattice of sodium chloride. Furthermore, depending on the polarity of the ions involved, it is able to interact electrostatically (or to form hydrogen bonds) generating forces that break the crystalline structure (in chemical lexicon this “siege” of the solute ions by the water molecules it is called solvatation).
The water is permanently present on the earth both in the liquid state, in the solid state and in the gaseous state (thus making life on earth possible as we know it).It is odorless, colorless and transparent (therefore it allows the photosynthesis of aquatic plants).The specific heat is very high (only hydrogen, helium and a few other substances have such a high specific heat, because the energy given to the water molecules when it is heated, in addition to shaking the molecules more, also serves to break the hydrogen bonds (starting from the liquefaction temperature, when the temperature rises, the hydrogen bonds begin to break, which are reduced as the temperature rises until it disappears with complete evaporation) .This feature is very useful for an optimal thermoregulation of the beings living, in addition the large amount of water present in the earth’s surface allows good climatic thermoregulation.
The latent heat of fusion is very high due to the fact that, once the evaporation temperature is reached, 75% of the hydrogen bonds are still present; also the latent heat of fusion is very high. These peculiarities are very important for the climate on earth, in fact the water thanks to these high latent heat can thermoregulate mitigating temperature fluctuations.Ice is 9% less dense than water and is an excellent insulation (floating in water allows life even in the waters in icy areas of the earth).The water molecule is so small and so light that it should evaporate at -80 ° C (and instead on earth, depending on atmospheric pressure, it evaporates between 68 ° C and 100 ° C) and should freeze -100 ° Cinstead of 0 ° C; reaches its maximum density at 3.98 ° C as well as its maximum degree of vitality (2).
(2) For further information see Viktor Schauber – anomalous point and state of indifference.