Base function (or hydroxide)

The base function is characterized by substances that present the hydroxyl group (OH)-1 bonded to metals. Due to the presence of this group, these substances are also called hydroxides. An example of this function is hydrated lime, used in wall paintings, whose formula is Ca (OH)2.

The bases are formed by hydroxyl anion (OH) ionic bonding- with a metal; they are therefore ionic compounds.

There is one exception, however, which is ammonium hydroxide (NH4OH), a base that has no metal in its formula, despite being an ionic compound.

At the bases, the hydroxyl anion has a hydrogen atom attached to an oxygen atom by electron sharing (covalent bonding); this hydroxyl anion has charge -1therefore forms an ionic bond with a cation.

Therefore, when isolated this anion has charge -1. Watch:

Base dissociation

Just as, in the presence of water, acids produce by ionization the cation H+, for a substance to belong to the base function it is necessary that when added to water it produces as anion exclusively hydroxyl (-OH).

See the following equations:

When dissolved in water, sodium hydroxide (NaOH) dissociates, yielding free ions. At+ and OH-.

Ionization and dissociation difference
Ionization is the formation of ions by breaking a covalent bond. That is, the source substance is not formed by ions and, after the covalent bond breakage, they are produced.
Dissociation It is the term applied to ionic compounds, that is, the separation of ions that already exist in these substances by some process.

Dissociation may also occur between bases with more than one hydroxyl.

In this example, in addition to cation Here2+, two hydroxyls are released on calcium hydroxide dissociation.

The bases are ionic compounds that dissociate in the presence of water, releasing anion (OH) - in solution.