Class 12 Ch 9 Coordination Compounds Chemistry Notes PDF

Stuck with coordination compounds that just look like bracketed chaos? Don’t worry, this chapter is way easier once you know who’s bonding with who. It’s all about metal ions bonding with ligands to form complex ions. That’s the core.

From types of ligands and charges to real-life uses and scoring questions, everything fits once the basics are clear. So if you're looking for no-fluff, exam-ready Class 12 Chemistry Coordination Compounds Notes, this is exactly where you should be.

Notes of Coordination Compounds Class 12 PDF Here

If you're stuck flipping definitions or getting confused between ligands and coordination spheres – pause right here. These Coordination and Compounds Class 12 Notes break down the basics without the overload. From central atoms to chelates, this is your clean-start guide to the chapter.

What Are Coordination Compounds? – Explained for Class 12 Chemistry

A coordination compound is a chemical compound where a central metal atom or ion is bonded to surrounding ions or molecules called ligands. These ligands donate lone pairs of electrons to form coordinate bonds with the metal.

Basically, it’s metal + ligands = one stable, charged unit inside square brackets. You’ve probably seen stuff like [Fe(CN)₆]⁴⁻ or [Cu(NH₃)₄]²⁺ in your NCERT - that’s a coordination compound.

Types of Components in a Coordination Compound

Coordination compounds consist of multiple parts working together. Here’s a quick breakdown of the main terms:

1. Central Atom/Ion

This is usually a transition metal like Cu²⁺, Fe³⁺, or Co³⁺. It sits at the center and accepts electrons from ligands to form the compound.

Example: In [Fe(CN)₆]³⁻, iron (Fe³⁺) is the central metal ion.

2. Ligands

Ligands are ions or molecules that donate electron pairs to the metal ion.

Types of ligands:

• Monodentate – donate one pair (e.g. NH₃, Cl⁻, CN⁻)
• Bidentate – donate two pairs (e.g. ethylenediamine or C₂O₄²⁻)
• Polydentate – donate more than two pairs (e.g. EDTA⁴⁻)
  

3. Coordination Number

This tells us how many ligand atoms are bonded to the central atom.

Example: In [Co(NH₃)₆]³⁺, the coordination number is 6.

4. Coordination Entity

This includes the metal ion and the ligands bonded to it. It’s always inside square brackets.

Example: [Cu(NH₃)₄]²⁺ is a coordination entity.

5. Counter Ions

These are ions outside the brackets that balance the overall charge.

Example: In [Co(NH₃)₆]Cl₃, the 3 Cl⁻ ions are counter ions.

In short: Coordination compounds are like mini chemical teams - the metal is the leader, and ligands are the loyal helpers that stick around by donating electrons.

Core Concepts in Coordination and Compounds Class 12 Notes

Coordination compounds follow two main ideas - oxidation number and coordination number. These decide the charge, structure, and naming of every compound in this chapter. Once you get these two, the rest becomes way easier

Two Main Ideas Every Coordination Compound Follows

Just like solids can be crystalline or amorphous, coordination compounds work around two constant rules:

1. Oxidation Number of the Central Atom

This tells you the charge carried by the central metal ion, after accounting for all the ligand charges. It helps in writing formulas, names, and balancing redox reactions.

To calculate:
Oxidation number of metal = (overall charge of complex) – (total charge of ligands)

Features:

• Written in Roman numerals in naming (e.g., Iron(III)
• Ligands can be neutral or negative
• Needed for both IUPAC naming and reactions

Example:
In [Fe(CN)₆]³⁻ → CN⁻ = –1 (x6 = –6), total charge = –3
⇒ Fe = +3 oxidation state

2. Coordination Number

This is the number of ligand atoms directly attached to the central metal ion. It’s always based on the number of bonds, not the total number of ligands.

Features:

• Helps determine the shape of the compound
• Doesn’t depend on the charge of the ligand
• Common values: 2, 4, or 6 (leading to linear, tetrahedral, or octahedral shapes)

Examples:

• [Cu(NH₃)₄]²⁺ → coordination number = 4 (tetrahedral)
• [Co(NH₃)₆]³⁺ → coordination number = 6 (octahedral)

Werner’s Theory – Included in Class 12th Coordination Compounds Notes

Werner’s theory was the first proper explanation of how coordination compounds are formed. He showed that metal ions don’t just stick to any atoms randomly - they follow a fixed pattern of bonding that explains both structure and properties.

Two Types of Valency in Werner’s Theory

Just like solids can be classified by particle arrangement, Werner’s theory divides valency like this:

1. Primary Valency (Ionisable)

This refers to the oxidation state of the central metal. These valencies are satisfied by anions like Cl⁻ or NO₃⁻ and can ionise in solution.
Features:

• Equal to oxidation number
• Satisfied by negative ions
• Ionisable (found outside the brackets)

Example: [Co(NH₃)₆]Cl₃ → Cl⁻ ions are primary valencies

2. Secondary Valency (Non-Ionisable)

This refers to the coordination number – the number of ligands directly attached to the metal ion. These don’t ionise in solution and stay bonded inside the brackets.
Features:

• Equal to coordination number
• Satisfied by ligands (neutral or negative)
• Non-ionisable (found inside the brackets)

Example: [Co(NH₃)₆]Cl₃ → NH₃ molecules are secondary valencies

Naming Rules from Class 12 Coordination Compounds Notes

Naming a coordination compound might look tricky, but once you know the order and rules, it’s actually super logical. You always start from the ligands, then the metal, and finally mention its oxidation number - all following IUPAC rules.

How to Name Coordination Compounds

Here’s the fixed step-by-step format used in Class 12 Chemistry Coordination Compounds Notes:

1. Naming the Ligands

List all ligands first - in alphabetical order, not by charge or number.

Rules:

• Anionic ligands end in –o (e.g., Cl⁻ → chloro, CN⁻ → cyano)
• Neutral ligands use their regular names (e.g., NH₃ → ammine, H₂O → aqua)
• Use prefixes: di–, tri–, tetra– (but bis–, tris– for complex ligands)

Example: [Co(NH₃)₄Cl₂]⁺ → tetraammine dichloro cobalt

2. Naming the Metal

After ligands, write the metal name. If the complex is anionic, the metal ends in –ate.

Rules:

• Mention the oxidation number in Roman numerals
• Use –ate for metals in negative complexes (e.g., ferrate, cuprate)

 Examples:

• [Co(NH₃)₆]³⁺ → hexaamminecobalt(III)
• [PtCl₆]²⁻ → hexachloroplatinate(IV)

Isomerism – Straight from Class 12 Chemistry Coordination Compounds Notes

Isomerism in coordination compounds is just like in organic chemistry - same formula, different arrangement. But here, it’s all about how ligands attach or where atoms sit. This concept is super important for both board exams and MCQs.

Types of Isomerism in Coordination Compounds

Here are the two major categories explained in Class 12 Chemistry Coordination Compounds Notes:

1. Structural Isomerism

This is when the connection or bonding of ligands changes. The compound still has the same formula, but the structure is different.

Types include:

• Ionisation isomerism: Produces different ions in solution
  → [Co(NH₃)₅Br]SO₄ vs. [Co(NH₃)₅SO₄]Br
  
  
• Hydrate isomerism: Water is inside vs. outside the coordination sphere
  → [Cr(H₂O)₆]Cl₃ vs. [Cr(H₂O)₅Cl]Cl₂·H₂O
  
  
• Linkage isomerism: Ligand bonds through different atoms (e.g., –NO₂ vs –ONO)

2. Stereoisomerism

Here, the bonding stays the same, but the spatial arrangement changes. It affects geometry, not formula.

Types include:

• Geometrical isomerism: Different positions of ligands (cis/trans)
  → [Pt(NH₃)₂Cl₂] → cis and trans forms

• ‍Optical isomerism: Mirror image compounds (non-superimposable) → Common in octahedral complexes with bidentate ligands (e.g., [Co(en)₃]³⁺)

Bonding Theories in Coordination Compounds Class 12 Notes

To explain how ligands stick to the central metal, we use bonding theories. These theories help us understand shapes, magnetism, and why some compounds are colored or not. Don’t stress - Class 12 Coordination Compounds Notes only need two main ones.

 Here are the Two Key Bonding Theories You Need to Know

1. Valence Bond Theory (VBT)

This theory explains bonding based on hybridisation of the central metal’s orbitals. It tells us about the shape and magnetic behaviour of the complex.

Features:

• Ligands donate electron pairs → metal uses empty orbitals to bond
• Predicts hybridisation (sp³, d²sp³, etc.)
• Tells if compound is paramagnetic (unpaired e⁻) or diamagnetic (no unpaired e⁻)

Example:

• [Fe(CN)₆]⁴⁻ → low-spin, inner d²sp³ hybridisation → diamagnetic
• [FeF₆]³⁻ → high-spin, outer sp³d² hybridisation → paramagnetic

2. Crystal Field Theory (CFT)

This theory looks at how ligand electric fields affect metal d-orbitals. It focuses on energy differences, not bonding.

Features:

• d-orbitals split into two levels in ligand field (e.g., t₂g and eₙ)
• Explains color, magnetic properties, and stability
• Doesn’t use hybridisation - only electrostatic concepts

Example:

• Octahedral fields: [CoF₆]³⁻ → weak field → high spin
• Tetrahedral fields: [NiCl₄]²⁻ → smaller splitting → always high spin

Real-Life Uses in Notes of Coordination Compounds Class 12

Coordination compounds aren't just chemical show-offs - they’re actually useful in everyday life. Here's a quick look at their real-world applications, right from Notes of Coordination Compounds Class 12:

Conclusion 

And that’s a wrap on Coordination Compounds – one of the trickiest-looking but actually super manageable chapters in Class 12 Chemistry. Sounds like a complex mess at first, right? But now that you’ve seen ligands, naming rules, isomerism, and bonding theories laid out clearly – it clicks.

If this blog helped even a little, that’s a solid win. One more chapter off your list, and you're officially ahead of the panic crowd.

FAQs 

Q1. What is a ligand in coordination compounds?
Ans. A ligand is an atom, ion, or molecule that donates a pair of electrons to the central metal atom to form a coordinate bond.

Q2. How are coordination compounds named?
Ans. They are named by listing ligands first in alphabetical order, followed by the central metal with its oxidation state in Roman numerals.

Q3. Why do coordination compounds show color?
Ans. Colors arise due to d-d transitions where electrons in the metal ion absorb light and jump between d-orbitals.

Q4. What is linkage isomerism?
Ans. It occurs when a ligand can bind to the metal through different atoms, creating isomers with different properties.

Q5. What is the chelate effect?
Ans. It’s the extra stability in coordination compounds formed by ligands that bind through multiple sites, forming ring structures.