Step 1: Understanding the Concept:
Werner's theory was the first successful explanation of the bonding and structure of coordination compounds.
Step 3: Detailed Explanation:
1. Metals in coordination compounds show two types of valency: Primary and Secondary.
2. Primary Valency: It is ionizable and corresponds to the oxidation state of the metal. It is satisfied by negative ions.
3. Secondary Valency: It is non-ionizable and corresponds to the coordination number. It is satisfied by negative ions or neutral molecules (ligands).
4. Secondary valencies are fixed for a metal and are directed in space toward specific positions, which determines the geometry of the complex.
Step 4: Final Answer:
Werner's postulates differentiate between ionizable oxidation states and non-ionizable coordination numbers.