Jons Berzelius (1779-1848)

Berzelius was a Swedish chemist. He classified different substances by calculating their atomic weights.
By 1818 he had accurately calculated the atomic weights of 45 elements and suggested a new way of naming the elements
by using the first letter or letters of their names, O = oxygen
Combinations of elements are represented by putting the letters together CO2 = Carbon dioxide, one carbon atom joined to two oxygen atoms.

Source : Wikipedia