HS 2nd year Chemistry Unit 5: Coordination Compounds Coordination

 

🔹 1. What are coordination compounds?

Answer:
Coordination compounds are compounds in which a central metal atom or ion is bonded to a fixed number of ions or molecules through coordinate bonds. These surrounding molecules or ions are called ligands.

Keywords with Bengali meanings:

• Coordination compound – সমযোজিত যৌগ

• Central metal atom/ion – কেন্দ্রীয় ধাতব পরমাণু/আয়ন

• Ligand – লিগ্যান্ড (বন্ধনকারী আয়ন বা অণু)

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🔹 2. State Werner’s theory of coordination compounds.

Answer:
Werner's theory states that:

1. Metals show two types of valencies: primary (ionisable) and secondary (non-ionisable).

2. Primary valencies are satisfied by negative ions.

3. Secondary valencies are satisfied by ligands and determine the geometry.

4. The secondary valencies form specific shapes like octahedral, tetrahedral, etc.

Keywords with Bengali meanings:

• Primary valence – প্রাথমিক সঁযোগ

• Secondary valence – গৌণ সঁযোগ

• Ionisable – আয়নীয়

• Geometry – জ্যামিতিক গঠন

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🔹 3. What is the difference between a double salt and a complex?

Answer:
Double salts dissociate completely into ions in water (e.g., Mohr’s salt), whereas complexes retain their identity and do not fully dissociate (e.g., [Fe(CN)6]⁴⁻).

Keywords with Bengali meanings:

• Double salt – যৌগিক লবণ

• Complex – সমযোজিত যৌগ

• Dissociate – বিযুক্ত হওয়া

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🔹 4. Define coordination entity, central atom/ion, and ligand.

Answer:

• Coordination entity: A central atom/ion bonded to ligands in a fixed arrangement.

• Central atom/ion: Metal ion to which ligands are bonded.

• Ligand: Ions/molecules donating electron pairs to the metal ion.

Keywords with Bengali meanings:

• Coordination entity – সমযোজিত সত্ত্বা

• Ligand – লিগ্যান্ড

• Central atom – কেন্দ্রীয় পরমাণু

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🔹 5. What is coordination number and coordination sphere?

Answer:

• Coordination number: Number of ligand donor atoms directly bonded to the central metal atom.

• Coordination sphere: The central metal ion and ligands within square brackets.

Keywords with Bengali meanings:

• Coordination number – সমযোজনা সংখ্যা

• Coordination sphere – সমযোজনা বলয়

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🔹 6. Define oxidation number, homoleptic and heteroleptic complexes.

Answer:

• Oxidation number: The hypothetical charge on the central atom if all ligands are removed.

• Homoleptic complex: All ligands are of the same type.

• Heteroleptic complex: More than one type of ligand is present.

Keywords with Bengali meanings:

• Oxidation number – জারণ সংখ্যা

• Homoleptic – সমজাতীয় লিগ্যান্ড বিশিষ্ট

• Heteroleptic – বিভিন্ন লিগ্যান্ড বিশিষ্ট

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🔹 7. What are unidentate, didentate, and polydentate ligands?

Answer:

• Unidentate: Donates one pair of electrons (e.g., NH₃)

• Didentate: Donates two pairs (e.g., ethylene diamine)

• Polydentate: Donates multiple pairs (e.g., EDTA⁴⁻)

Keywords with Bengali meanings:

• Unidentate – একদন্তীয়

• Didentate – দ্বিদন্তীয়

• Polydentate – বহুদন্তীয়

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🔹 8. Explain chelation and ambidentate ligands.

Answer:

• Chelation: Formation of ring structures when a ligand binds through multiple atoms.

• Ambidentate: Ligands with two donor atoms but only one binds at a time (e.g., NO₂⁻ binds via N or O).

Keywords with Bengali meanings:

• Chelation – চেলেশন (বহুবন্ধন তৈরি)

• Ambidentate – দ্বিমুখী লিগ্যান্ড

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🔹 9. Describe the types of isomerism in coordination compounds.

Answer:

• Structural isomerism: Includes linkage, coordination, ionisation, and solvate isomerism.

• Stereoisomerism: Includes geometrical and optical isomerism.

Keywords with Bengali meanings:

• Isomerism – সমসূত্রীয়তা

• Geometrical isomerism – জ্যামিতিক সমসূত্রীয়তা

• Optical isomerism – আলোকীয় সমসূত্রীয়তা

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🔹 10. Explain the valence bond theory (VBT) for bonding in coordination compounds.

Answer:
According to VBT, metal ions hybridise orbitals (like sp³, dsp², d²sp³) to accept electron pairs from ligands, forming stable geometrical structures.

Keywords with Bengali meanings:

• Valence bond theory – সঁযোজক বন্ধন তত্ত্ব

• Hybridisation – সংকরীকরণ

• Geometry – জ্যামিতিক গঠন

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🔹 11. What is crystal field theory (CFT)?

Answer:
CFT explains bonding based on the electrostatic interaction between metal ions and ligands, causing d-orbital splitting into different energy levels.

Keywords with Bengali meanings:

• Crystal field theory – স্ফটিক ক্ষেত্র তত্ত্ব

• d-orbital splitting – d-কক্ষের বিভাজন

• Spectrochemical series – বর্ণ রসায়নিক শ্রেণি

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🔹 12. What causes colour in coordination compounds?

Answer:
The colour arises from d–d electronic transitions within the metal ion under the influence of ligands, absorbing visible light.

Keywords with Bengali meanings:

• Colour – বর্ণ

• d–d transition – d–d স্থানান্তর

• Absorption – শোষণ

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🔹 13. Describe the structure and bonding in metal carbonyls.

Answer:
Metal carbonyls have σ bonding from CO to metal and π-back bonding from metal d-orbital to CO's empty π* orbital, resulting in strong synergic bonding.

Keywords with Bengali meanings:

• Metal carbonyl – ধাতব কার্বোনাইল

• σ bond – সিগমা বন্ধন

• π-back bonding – পাই ব্যাক বন্ধন

• Synergic bonding – সহযোগী বন্ধন

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🔹 14. Mention some applications of coordination compounds.

Answer:

• Used in extraction of metals (e.g., gold, silver)

• In biological systems (e.g., haemoglobin, chlorophyll)

• Analytical chemistry (e.g., detection using EDTA)

• Medicine (e.g., cisplatin for cancer treatment)

• Electroplating and photography

Keywords with Bengali meanings:

• Extraction – নিষ্কাশন

• Biological system – জীবগত প্রক্রিয়া

• Electroplating – তড়িৎআবরণ

• Chelate therapy – চেলেট চিকিৎসা

📘 Worksheet: Coordination Compounds (Chapter 5 - Chemistry Class 12)

Name: ___________________
Class: XII  Date: _______________

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✍️ Section A – Short Answer Questions

Q1. Define coordination compounds.
✒️ ____________________________________________________________________
✒️ ____________________________________________________________________
📌 Keyword: Coordination compound – সমযোজিত যৌগ

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Q2. State any two postulates of Werner’s theory.
✒️ ____________________________________________________________________
✒️ ____________________________________________________________________
📌 Keywords: Primary valence – প্রাথমিক সঁযোগ, Secondary valence – গৌণ সঁযোগ

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Q3. Differentiate between a double salt and a coordination compound.
✒️ ____________________________________________________________________
✒️ ____________________________________________________________________
📌 Keywords: Double salt – যৌগিক লবণ, Dissociate – বিযুক্ত হওয়া

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Q4. What is meant by ligand? Give one example.
✒️ ____________________________________________________________________
📌 Keyword: Ligand – লিগ্যান্ড

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Q5. Define coordination number and coordination sphere.
✒️ ____________________________________________________________________
📌 Keywords: Coordination number – সমযোজনা সংখ্যা, Coordination sphere – সমযোজনা বলয়

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Q6. What is the oxidation number of the metal in [Fe(CN)6]⁴⁻?
✒️ ____________________________________________________________________
📌 Keyword: Oxidation number – জারণ সংখ্যা

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🧠 Section B – Conceptual Understanding

Q7. Explain the difference between homoleptic and heteroleptic complexes.
✒️ ____________________________________________________________________
✒️ ____________________________________________________________________
📌 Keywords: Homoleptic – সমজাতীয় লিগ্যান্ড বিশিষ্ট, Heteroleptic – বিভিন্ন লিগ্যান্ড বিশিষ্ট

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Q8. Define unidentate, didentate and polydentate ligands with examples.
✒️ ____________________________________________________________________
📌 Keywords: Unidentate – একদন্তীয়, Didentate – দ্বিদন্তীয়, Polydentate – বহুদন্তীয়

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Q9. What are chelating and ambidentate ligands? Give one example of each.
✒️ ____________________________________________________________________
📌 Keywords: Chelation – চেলেশন, Ambidentate – দ্বিমুখী লিগ্যান্ড

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Q10. Name two types of isomerism shown by coordination compounds.
✒️ ____________________________________________________________________
📌 Keywords: Geometrical isomerism – জ্যামিতিক সমসূত্রীয়তা, Optical isomerism – আলোকীয় সমসূত্রীয়তা

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🧪 Section C – Theory Based Questions

Q11. State the basic concept of Valence Bond Theory (VBT).
✒️ ____________________________________________________________________
📌 Keywords: Hybridisation – সংকরীকরণ, Valence Bond Theory – সঁযোজক বন্ধন তত্ত্ব

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Q12. Describe d-orbital splitting in Crystal Field Theory.
✒️ ____________________________________________________________________
📌 Keyword: Crystal Field Theory – স্ফটিক ক্ষেত্র তত্ত্ব, d-orbital splitting – d-কক্ষের বিভাজন

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Q13. Why are many coordination compounds coloured?
✒️ ____________________________________________________________________
📌 Keyword: d–d transition – d–d স্থানান্তর, Absorption – শোষণ

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Q14. Write a note on bonding in metal carbonyls.
✒️ ____________________________________________________________________
📌 Keywords: Metal carbonyl – ধাতব কার্বোনাইল, Synergic bonding – সহযোগী বন্ধন

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Q15. Mention any three applications of coordination compounds in daily life.
✒️ ____________________________________________________________________
📌 Keywords: Electroplating – তড়িৎআবরণ, Chelate therapy – চেলেট চিকিৎসা