Werner's Theory — Primary and secondary valency
Coordination Compounds
15
JEE Qs
8%
Hard
60
min
Master the definitions of primary and secondary valency and practice their application to determine the structure, number of ions, and properties of various coordination complexes.
✅ Key Points for JEE
- 1Primary valency corresponds to the oxidation state of the central metal ion; it is ionizable, non-directional, and satisfied by anions.
- 2Secondary valency corresponds to the coordination number of the central metal ion; it is non-ionizable, directional, and satisfied by ligands (anions or neutral molecules), dictating the complex's geometry.
- 3A single ligand can sometimes satisfy both primary and secondary valencies simultaneously if it is an anion and acts as a coordinating ligand.
- 4Werner's theory successfully explained the distinct properties (e.g., conductivity, number of ions, isomerism) of various coordination compounds.
⚠️ Common Mistakes
- ✕Confusing primary and secondary valencies, especially regarding their ionizability and directional nature.
- ✕Incorrectly identifying which ligands satisfy primary valency, secondary valency, or both in a given complex.
- ✕Failing to accurately determine the oxidation state (primary valency) and coordination number (secondary valency) of the central metal ion.
📝 Practice Questions
See allQ74.In the Claisen-Schmidt reaction to prepare, dibenzalacetone from 5.3 g of benzaldehyde, a total of 3.51 g of product was obtained. The percentage yield in this reaction was ______ %.
Q61.The calculated spin-only magnetic moments of K3 [Fe(OH)6] and K4 [Fe(OH)6] respectively are : (1) 3.87 and 4.90 B.M. (2) 4.90 and 5.92 B.M. (3) 4.90 and 4.90 B.M. (4) 5.92 and 4.90 B.M.
Q54.Identify the homoleptic complexes with odd number of d electrons in the central metal : (A) [FeO4]2− (B) [Fe(CN)6]3− (C) [Fe(CN)5NO]2− (D) [CoCl4]2− (E) [Co(H2O)3 F3] Choose the correct answer from the options given below : (1) (A), (B) and (D) only (2) (C) and (E) only (3) (B) and (D) only (4) (A), (C) and (E) only
Q68.In which of the following complexes the CFSE, Δo will be equal to zero? (1) [Fe(en)3]Cl3 (2) K4 [Fe(CN)6] (3) [Fe(NH3)6]Br2 (4) K3 [Fe(SCN)6]
Q70.From the magnetic behaviour of [NiCl4]2− (paramagnetic) and [Ni(CO)4] (diamagnetic), choose the correct geometry and oxidation state. (1) [NiCl4]2−: NiII , tetrahedral [Ni(CO)4] : NiII , (2) [NiCl4]2− : NiII , square planar [Ni(CO)4] : Ni(0) square planar , square planar (3) [NiCl4]2−: NiII , tetrahedral [Ni(CO)4] : Ni(0), (4) [NiCl4]2−: Ni(0), tetrahedral [Ni(CO)4] : Ni(0), tetrahedral square planar
Q53.The correct order of the following complexes in terms of their crystal field stabilization energies is : (1) [Co(NH3)4]2+ < [Co(NH3)6]2+ < [Co(en)3]3+ < [Co(NH3)6]3+ (2) [Co(NH3)6]2+ < [Co(NH3)6]3+ < [Co(NH3)4]2+ < [Co(en)3]3+ (3) [Co(en)3]3+ < [Co(NH3)6]3+ < [Co(NH3)6]2+ < [Co(NH3)4]2+ (4) [Co(NH3)4]2+ < [Co(NH3)6]2+ < [Co(NH3)6]3+ < [Co(en)3]3+
NCERT Chapters
- Class 12 Chemistry Ch 9: Coordination Compounds