Werner's Theory
The 1893 theory proposing that metals exhibit two types of valence and that ligands occupy fixed positions in space around the metal.
Unit
Dimensionless
In depth
Werner explained why CoCl₃·6NH₃ and CoCl₃·5NH₃ behave so differently by proposing a fixed inner sphere with definite geometry plus a variable outer sphere. Conductivity measurements and the isolation of predicted isomers confirmed the model and won him the 1913 Nobel Prize.
Examples in the real world
Predicting correctly that [Co(NH₃)₄Cl₂]⁺ would exist as two isomers, violet cis and green trans.