Svante Arrhenius won the 1903 Nobel Prize in Chemistry for proposing the theory of electrolytic dissociation. His theory explained why certain substances conduct electricity when dissolved in water: they split into electrically charged particles called ions.
Arrhenius developed this idea in his 1884 doctoral thesis at Uppsala University. The proposal initially met resistance because many chemists believed dissolved compounds remained intact. Later experiments on conductivity and chemical reactions supported his interpretation.
His work helped establish the modern concept of acids and bases. In the Arrhenius definition, an acid increases hydrogen-ion concentration in water, while a base increases hydroxide-ion concentration. The definitions are limited to aqueous solutions, but they remain useful in introductory chemistry.
Arrhenius also contributed to physical chemistry, including studies of reaction rates and the greenhouse effect. He was the first Swedish scientist to receive a Nobel Prize. Wilhelm Ostwald, another pioneer of physical chemistry, was awarded the Chemistry Nobel in 1909, not 1903.