Is there something seemingly simpler than the water? Despite its apparent simplicity this we know so well fluid is complex and still not well understood. Water is endowed with some exceptional properties physical, chemical which constitute its specificity. As demonstrates this article, the structure microscopic liquid water, which is in based on these properties, is research a topic may provide some news.
Water is one of the four “elements” that the Greek philosopher Aristotle had defined as constituents of the universe (the others being air, earth and fire). We still do not understand it best. Given our familiarity with the water, the fact is no less surprising. Oceans, lakes, rivers, rainfall, abundant in almost all regions of the Earth, water is largely determined by the landscapes and climates.
Very often it is synonymous with life: water is an essential component of the structure and metabolism of all living things. Certainly, the primary role of water must be attributed to chance it derives from its unique physical and chemical properties. An example of a biologically important property of water is the hydrophobic effect, ie the fact that hydrocarbon CH groups tend to be repelled by water molecules. This effect is responsible, in part at least, of the complex spatial structures that present proteins, DNA and lipid bilayers of cell membranes.
In the absence of water, all these structures would be unstable. It said that even without much risk of error, that this effect might play a role in the emergence of life on Earth. But the hydrophobic effect is not the only interesting property of water. In what follows we will find others.
Why is water a chemical so privileged? The answer, of course, lies in the molecule and its interactions with the environment. Water molecules are relatively well known, but the interactions. set in a group of water molecules are less so. However, it is these that largely contribute to a liquid water is exceptional.
Water was considered as a single body until the eighteenth century. In 1781 the chemical (and theologian) English Joseph Priestley made by combustion synthesis of hydrogen. Chemicals Antoine-Laurent Lavoisier and Henrv Cavendish proved that water was composed of hydrogen and oxygen. Later in 1805 the French chemist Louis-Joseph Gay-Lussac and sage von Humboldt, Prussian Alexandei determined that the volume ratio of hydrogen / oxygen value 2, which ultimately led to the molecular formula H20. The water molecule consists of two hydrogen atoms and one oxygen atom.
In the molecule H, O, each hydrogen atom is bonded to the oxygen atom by a covalent bond. In this connection, relatively strong, the hydrogen atom and the oxygen atom they share one electron each. These atoms gain an electron and added: the hydrogen atom with two electrons is instead of one oxygen and peripherals with eight electrons instead of six (he participates in two links). As we know, these numbers correspond to full outer electron shells that confer greater stability to the molecule.
The distribution of the electrons in the OH covalent bond is not symmetrical: the electrons are more strongly attracted to the oxygen atom by hydrogen. As a result, the oxygen becomes negatively charged and the hydrogens positively. This imbalance in the distribution of electrical charges, added to the non-linear geometry of the water molecule, results in the existence of a “dipole moment – electric”. This electrical imbalance is responsible for the great solvent power of water for ionic crystals with (certain salts, acids or bases). Water molecules can be inserted between the glass constituent ions moving towards them the opposite electrical charge. The resulting shielding considerably weakens the attraction between the ion crystal, reducing the cohesion of the crystal and facilitating its dissolution.
