Question

Which statement is logical according to Werner's theory?

• A. Primary valency can be ionized
• B. Secondary valency can be ionized
• C. Primary and secondary valency do not ionize
• D. Only primary valency does not ionize

Hint:

Werner's theory states that primary valency is ionizable and corresponds to oxidation state, while secondary valency is non-ionizable and corresponds to coordination number.

Answer 1

The Correct Option is A

Concept: Werner's coordination theory was proposed to explain the structure and properties of coordination compounds. According to Werner, a metal ion exhibits two types of valencies:
• Primary valency
• Secondary valency Primary valency corresponds to the oxidation state of the metal ion and is generally satisfied by negative ions. Secondary valency corresponds to the coordination number and is satisfied by ligands directly attached to the metal ion. A key distinction between these two valencies is their ionization behavior in aqueous solution.

Step 1: Understanding primary valency. Primary valency is equivalent to the oxidation state of the central metal atom. For example, in \[ [Co(NH_3)_6]Cl_3 \] the oxidation state of cobalt is \[ +3. \] Thus the primary valency is three. These valencies are satisfied by chloride ions present outside the coordination sphere.

Step 2: Understanding ionization of primary valency. The chloride ions outside the coordination sphere can dissociate in water. \[ [Co(NH_3)_6]Cl_3 \rightarrow [Co(NH_3)_6]^{3+}+3Cl^{-} \] Thus the ions satisfying primary valency are ionizable. Hence primary valency can ionize.

Step 3: Understanding secondary valency. Secondary valency is satisfied by ligands directly attached to the metal. In \[ [Co(NH_3)_6]Cl_3 \] the six ammonia molecules satisfy secondary valency. Since these ligands are present inside the coordination sphere, they do not ionize under ordinary conditions.

Step 4: Checking each option. Option (A): Primary valency can be ionized. Correct. Option (B): Secondary valency can be ionized. Incorrect because ligands inside the coordination sphere are non-ionizable. Option (C): Both do not ionize. Incorrect. Option (D): Only primary valency does not ionize. Incorrect.

Step 5: Final conclusion. According to Werner's theory, primary valencies are ionizable whereas secondary valencies are non-ionizable. Therefore, \[ \boxed{(A)} \]