Acids and bases - Broensted-Lowry definition
A more fundamental definition of acids and bases than the one provided on the index page was given by the Danish chemists Johannes Broensted.
The definitions are:
A Broensted acid is a proton doner.
A Broensted base is a proton acceptor.
The English chemist, Thomas Lowry, proposed exactly the same at roughly the same time so this is all called the Broensted Lewry theory.
The theory can be visualized (figure 1)
Fig 1. The proton is transferred from the acid to the base
So in terms of speaking about acids and bases it this context, a proton is H+. Please remember that hydrogen only consist of a proton and a single electron giving the neutral charge. Without the electron only the proton is left, that is H+.
So, we can have both weak and strong acids. A weak acid is not very prone to release its proton while a strong acid will immediately donate its proton to anything that comes close.
In terms of definitions, a strong acid is fully ionized in aqueous solutions at normal concentrations. A weak acid is only partially ionized.
E.g. a solution of acetic acid held at pH 5.6, only approx. 10% is on the protonized form (CH3COOH) while 90% is ionized and in the form CH3COO-, having a negative charge since it has donated its proton H+ to water (H2O) yielding the hydronium ion.
Web references
Broensted-Lowry definition at Wikipedia
Concept explained
Broensted-Lowry at Salisbury University