Werner's Theory of Coordination Compounds
### Introduction
Werner's Theory, proposed by Alfred Werner in 1893, was the first successful explanation of the
structure
of coordination compounds. He received the Nobel Prize in Chemistry in 1913 for his work.
### Postulates of Werner's Theory
1. **Dual Valency Concept**: Metal ions exhibit two types of valencies:
- **Primary Valency (Ionizable valency)**: Corresponds to oxidation state and is satisfied by
negative ions.
- **Secondary Valency (Non-ionizable valency)**: Represents the coordination number and is
satisfied by ligands.
2. **Fixed Coordination Number**: Each metal has a fixed number of secondary valencies,
determining its geometry.
3. **Spatial Arrangement of Ligands**: The ligands occupy specific positions around the metal ion,
leading to distinct geometries.
4. **Ionizability**: Primary valency satisfies ionic bonds, while secondary valency forms coordination
bonds.
### Primary and Secondary Valency
- **Primary Valency**: Corresponds to the oxidation state (e.g., in [CoCl3(NH3)3], Co has +3
oxidation state).
- **Secondary Valency**: Defines the coordination number (e.g., 6 for Co in [CoCl3(NH3)3], forming
an octahedral structure).
### Experimental Evidence Supporting Werner's Theory
1. **Ionization Studies**: Different compounds with the same molecular formula exhibited varying
electrical conductivity,
supporting the presence of non-ionizable secondary valencies.
2. **Isomerism**: Werner's theory explained geometrical and optical isomerism in coordination
complexes.
3. **Precipitation Reactions**: Only free chloride ions reacted with silver nitrate, confirming the
### Introduction
Werner's Theory, proposed by Alfred Werner in 1893, was the first successful explanation of the
structure
of coordination compounds. He received the Nobel Prize in Chemistry in 1913 for his work.
### Postulates of Werner's Theory
1. **Dual Valency Concept**: Metal ions exhibit two types of valencies:
- **Primary Valency (Ionizable valency)**: Corresponds to oxidation state and is satisfied by
negative ions.
- **Secondary Valency (Non-ionizable valency)**: Represents the coordination number and is
satisfied by ligands.
2. **Fixed Coordination Number**: Each metal has a fixed number of secondary valencies,
determining its geometry.
3. **Spatial Arrangement of Ligands**: The ligands occupy specific positions around the metal ion,
leading to distinct geometries.
4. **Ionizability**: Primary valency satisfies ionic bonds, while secondary valency forms coordination
bonds.
### Primary and Secondary Valency
- **Primary Valency**: Corresponds to the oxidation state (e.g., in [CoCl3(NH3)3], Co has +3
oxidation state).
- **Secondary Valency**: Defines the coordination number (e.g., 6 for Co in [CoCl3(NH3)3], forming
an octahedral structure).
### Experimental Evidence Supporting Werner's Theory
1. **Ionization Studies**: Different compounds with the same molecular formula exhibited varying
electrical conductivity,
supporting the presence of non-ionizable secondary valencies.
2. **Isomerism**: Werner's theory explained geometrical and optical isomerism in coordination
complexes.
3. **Precipitation Reactions**: Only free chloride ions reacted with silver nitrate, confirming the
