Introduction
Coordination Compounds form one of the most important and scoring chapters of Class 12 Chemistry. This chapter is frequently asked in CBSE Board Exams, State Boards, NEET, JEE Mains, and other competitive examinations. Students usually search for Coordination Compounds Class 12 Notes to get clear concepts, easy explanations, IUPAC naming rules, isomerism, bonding theories, and important reactions. These notes are prepared strictly exam-based, using simple language, and cover all important topics as per the latest syllabus.
Coordination Compounds Class 12 Notes | Chemistry Full Notes for Board Exam
What are Coordination Compounds?
A coordination compound is a compound in which the central metal atom or ion is bonded to a fixed number of ions or molecules called ligands through coordinate (dative) bonds.
Example:
- [Co(NH3)6]Cl3
- K4[Fe(CN)6]
In coordination compounds, the metal ion acts as a Lewis acid (electron pair acceptor) and ligands act as Lewis bases (electron pair donors).
Important Terms and Definitions
1. Central Metal Atom/Ion
The metal atom or ion to which ligands are attached.
Example: Co³⁺ in [Co(NH3)6]Cl3
2. Ligands
Ions or molecules that donate a pair of electrons to the central metal atom.
Examples: NH3, H2O, CN⁻, Cl⁻
3. Coordination Number
The total number of ligand donor atoms attached to the central metal atom.
Example: Coordination number of Co³⁺ in [Co(NH3)6]³⁺ is 6.
4. Coordination Sphere
The central metal ion and ligands enclosed within square brackets.
Example: [Co(NH3)6]³⁺
5. Oxidation Number
The charge on the central metal ion assuming all ligands are removed as ions.
Types of Ligands
Based on Denticity
- Monodentate Ligands – Bind through one donor atom
- Examples: NH3, H2O, Cl⁻
- Bidentate Ligands – Bind through two donor atoms
- Example: Ethylenediamine (en)
- Polydentate Ligands – Bind through more than two donor atoms
- Example: EDTA⁴⁻ (Hexadentate)
Chelating Ligands
Ligands that form ring structures with the metal ion are called chelating ligands.
Werner’s Theory of Coordination Compounds
Alfred Werner proposed this theory to explain the structure of coordination compounds.
Main Postulates:
- Metals have two types of valencies:
- Primary valency (Ionizable)
- Secondary valency (Non-ionizable)
- Primary valency = Oxidation state
- Secondary valency = Coordination number
- Secondary valencies are directional
Example: [Co(NH3)6]Cl3
- Primary valency = 3
- Secondary valency = 6
Nomenclature of Coordination Compounds (IUPAC Rules)
Steps for Naming:
- Name the cation first, then the anion
- Name ligands in alphabetical order
- Use prefixes: di-, tri-, tetra-, penta-, hexa-
- Neutral ligands: NH3 = ammine, H2O = aqua
- Negative ligands end with -o
- Oxidation state of metal written in Roman numerals
Example:
[Co(NH3)6]Cl3 → Hexaamminecobalt(III) chloride
Isomerism in Coordination Compounds
Structural Isomerism
- Linkage Isomerism
- Example: [Co(NH3)5NO2]Cl2 and [Co(NH3)5ONO]Cl2
- Coordination Isomerism
- Example: [Co(NH3)6][Cr(CN)6]
Stereoisomerism
- Geometrical Isomerism
- Cis-trans isomerism
- Optical Isomerism
- Non-superimposable mirror images
Bonding in Coordination Compounds
Valence Bond Theory (VBT)
According to VBT, the central metal ion uses hybrid orbitals to bond with ligands.
Types of Complexes:
- Inner orbital complexes (d²sp³)
- Outer orbital complexes (sp³d²)
Limitations of VBT
- Cannot explain color
- Cannot explain magnetic properties accurately
Crystal Field Theory (CFT)
CFT explains bonding based on electrostatic attraction between metal ions and ligands.
Crystal Field Splitting
- Octahedral field
- Tetrahedral field
Strong field ligands cause pairing of electrons, weak field ligands do not.
Importance and Applications of Coordination Compounds
- Hemoglobin (Fe complex) carries oxygen
- Chlorophyll (Mg complex) for photosynthesis
- Used in electroplating
- Used in medicines (cisplatin)
- Used in qualitative analysis
Important Exam-Oriented Points
- Learn IUPAC naming carefully
- Practice oxidation number calculations
- Isomerism is highly scoring
- Short notes questions are common
FAQs – Coordination Compounds Class 12 (Students’ Most Searched Questions)
Q1. What are coordination compounds in Class 12 Chemistry?
Coordination compounds are compounds in which a central metal atom or ion is surrounded by ions or molecules called ligands, which are linked to the metal through coordinate bonds.
Q2. Is Coordination Compounds an important chapter for board exams?
Yes, Coordination Compounds is one of the most important and high-weightage chapters in Class 12 Chemistry. Questions from this chapter are frequently asked in CBSE board exams, including naming, isomerism, and bonding.
Q3. Which topics are most important in Coordination Compounds Class 12?
The most important topics are:
- IUPAC nomenclature
- Werner’s theory
- Types of ligands
- Isomerism (linkage, geometrical, optical)
- Valence Bond Theory
- Crystal Field Theory
Q4. How many marks are asked from Coordination Compounds in Class 12 board exam?
Generally, 4–6 marks questions are asked from Coordination Compounds in the Class 12 Chemistry board exam, including short and long answer questions.
Q5. Is Coordination Compounds important for NEET and JEE?
Yes, this chapter is very important for NEET, JEE Mains, and other competitive exams. MCQs related to ligands, hybridization, and magnetic behavior are commonly asked.
Q6. What is the easiest way to remember IUPAC naming of coordination compounds?
The easiest way is to follow a step-by-step approach, practice daily, remember common ligand names, and solve previous years’ board questions.
Q7. What is the difference between primary and secondary valency?
Primary valency is ionizable and equal to the oxidation state, while secondary valency is non-ionizable and equal to the coordination number.
Q8. Which ligands are strong field ligands in Class 12 syllabus?
Common strong field ligands include CN⁻, CO, NO₂⁻, while weak field ligands include H₂O, F⁻, Cl⁻.
Q9. Why are coordination compounds colored?
Coordination compounds are colored due to d–d electronic transitions when electrons absorb visible light and jump between split d-orbitals.
Q10. Can I score full marks in Coordination Compounds by studying notes only?
Yes, if you study clear notes, practice numerical problems, IUPAC naming, and previous year questions, you can easily score full marks from this chapter.
Conclusion
Coordination Compounds is a conceptual but scoring chapter in Class 12 Chemistry. With proper understanding of definitions, nomenclature, isomerism, and bonding theories, students can easily score full marks from this chapter. These Coordination Compounds Class 12 Notes are designed to help students revise quickly and perform confidently in exams.