Werner, Alfred (1866–1919)

French-born Swiss chemist. He was awarded the Nobel Prize for Chemistry in 1913 for his work on valency theory, which gave rise to the concept of coordinate bonds and coordination compounds.

Werner demonstrated that different three-dimensional arrangements of atoms in inorganic compounds gives rise to optical isomerism (the rotation of polarized light in opposite directions by molecules that contain the same atoms but are mirror images of each other).

Werner was born in Mulhouse, Alsace, and studied in Switzerland at the Zürich Polytechnic, becoming professor there in 1895.

In addition to ionic and covalent bonds, Werner proposed the existence of a set of coordination bonds resulting from an attractive force from the centre of an atom acting uniformly in all directions. The number of groups, or ligands, that can thus be bonded to the central atom depends on its coordination number and determines the structure (geometry) of the resulting molecules. Neutral ligands (such as ammonia and water) leave the central atom's ionic charge unchanged; ionic ligands (such as chloride or cyanide ion) alter the central charge accordingly.