1. Composition and structure of the water molecule

1.1 Chemical nature of pure water

The water molecule can break down into gaseous elements or dissociate into ions, giving it a variety of scientific names:

• thermolysis (partially achieved by Lavoisier in 1785, as we saw above, at a temperature of around 750°C ; it would not be complete until around 3,000°C) or by electrolysis (first performed by Volta in 1800), we obtain hydrogen and oxygen, which shows that water is a hydrogen (or dihydrogen) oxide or an oxygen acid (we also sometimes say that water is an oxygen hydride, which is in fact incorrect, as this expression does not meet the definition of a hydride where the H atom is electronegative);

• by autoprotolysis, it partially dissociates: