Water

Water molecule consists of one oxygen atom covalently bonded to two hydrogen atoms: H-O-H The covalent bond is very strong, hence the energy to be delivered to break is great. Until 1781 it was believed that water was indestructible and unchanging substance, but Cavendish proves otherwise, and checks Lavoisier in 1783.

In terms of mass, 16 g of oxygen is associated with 2.16 g of hydrogen. The linear molecular structure H - O - H, can not explain their behavior and properties, is just a way to symbolize. Actually occurs spatially as a large sphere (oxygen atoms) of two areas that leave girls like protrusions or ears (hydrogen atoms) arranged angularly and one side. The angle formed by the three atoms is 105 degrees.

This angular disposition of the atomic bonds causes a charge density distribution on the molecule that produces a polarization. Thus we see that one end is electro-positive (on the side are the protons) and the other is electronegative. The polarization is the cause of one of the unique properties of water: Their ability and therefore solvent combination to form compounds.

The polarization is also responsible for intermolecular binding of a molecule of water with others. The electrical interactions between the hydrogen molecule and relatively free electron pairs of oxygen on the other, leading to a molecular link called "hydrogen bonds". For this type of link each water molecule has the opportunity to join four others in an "elastic".

This particular link will determine, according to the conditions of pressure and temperature, the distance between a water molecule to the other, allowing the distance as the water has any of its three states: solid, liquid or vapor.

Basic properties:
Properties Value
chemical formula H2O
molecular weight 18.0153 g/mol
phase liquid (at STP)
melting point 0 °C
boiling point 100 °C
density 1 g/cm3

Liquid properties:
Properties Value
vapor pressure 17.5 mmHg (at 20 °C)
dynamic viscosity 8.9×10-4 Pa s (at 25 °C)
surface tension 0.0728 N/m
refractive index 1.333
UV cutoff wavelength 191 nm