HS 2nd year Chemistry Unit 4:The d- and f Block Elements The d - and f Block Element

 

🟢 Topic: Introduction to d- and f-Block Elements

Q1. What are d-block and f-block elements?
Answer:
The d-block elements are those in which the d-orbitals are progressively filled, found in groups 3 to 12 of the periodic table. The f-block elements are those in which the 4f and 5f orbitals are progressively filled. They are placed separately at the bottom of the periodic table.

Keywords with Bengali Meaning:

• d-orbitals – d-কক্ষপথগুলি

• f-orbitals – f-কক্ষপথগুলি

• progressively filled – ক্রমশ পূর্ণ হয়

• periodic table – আবর্ত সারণি

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Q2. Why are zinc (Zn), cadmium (Cd), and mercury (Hg) not considered transition metals?
Answer:
Zinc, cadmium, and mercury have completely filled d-subshells (d¹⁰ configuration) in their ground states and common oxidation states, so they are not considered transition metals.

Keywords with Bengali Meaning:

• transition metals – স্থানান্তর ধাতু

• oxidation states – জারণ অবস্থা

• ground state – ভূমিস্থিতি

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🟢 Topic: Electronic Configurations of d-Block Elements

Q3. Write the general electronic configuration of d-block elements.
Answer:
The general electronic configuration of d-block elements is (n–1)d¹⁻¹⁰ ns¹⁻². For example, Cr: [Ar] 3d⁵ 4s¹ and Cu: [Ar] 3d¹⁰ 4s¹ due to extra stability of half-filled and completely filled orbitals.

Keywords with Bengali Meaning:

• electronic configuration – তড়িৎ বিন্যাস

• half-filled – অর্ধ পূর্ণ

• completely filled – সম্পূর্ণ পূর্ণ

• stability – স্থিতিশীলতা

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Q4. Why does chromium have the configuration 3d⁵ 4s¹ instead of 3d⁴ 4s²?
Answer:
Chromium prefers 3d⁵ 4s¹ because half-filled d-orbitals (3d⁵) offer extra stability due to symmetrical distribution and exchange energy.

Keywords with Bengali Meaning:

• exchange energy – বিনিময় শক্তি

• symmetrical distribution – সমবণ্টন

• configuration – বিন্যাস

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🟢 Topic: General Properties of Transition Elements

Q5. Mention some physical properties of transition elements.
Answer:
Transition elements have high melting and boiling points, metallic lustre, high tensile strength, good conductivity, and hardness (except Zn, Cd, Hg).

Keywords with Bengali Meaning:

• metallic lustre – ধাতব দীপ্তি

• tensile strength – প্রসারণ শক্তি

• conductivity – পরিবাহিতা

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Q6. Why do transition elements have high melting and boiling points?
Answer:
Due to the involvement of (n–1)d electrons along with ns electrons in metallic bonding, which leads to stronger bonds.

Keywords with Bengali Meaning:

• metallic bonding – ধাতব বন্ধন

• boiling point – স্ফুটনাঙ্ক

• melting point – গলনাঙ্ক

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Q7. What is lanthanoid contraction?
Answer:
Lanthanoid contraction is the gradual decrease in atomic and ionic size from La to Lu due to poor shielding of f-electrons.

Keywords with Bengali Meaning:

• contraction – সংকোচন

• shielding effect – আবরণ প্রভাব

• ionic size – আয়নিক আকার

🧪 Worksheet: The d- and f-Block Elements (Part 1)

Class 12 – Chemistry | Chapter 4
Name: ___________ Roll No: ________ Date: ___________

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Section A: Very Short Answer Questions

(Answer in 1–2 sentences)

Q1. What is the general electronic configuration of d-block elements?
Ans: ___________________________________________________________

Q2. Why is Zn not considered a transition metal?
Ans: ___________________________________________________________

Q3. Which element has the configuration [Ar] 3d⁵ 4s¹ and why?
Ans: ___________________________________________________________

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Section B: Short Answer Questions

(Answer in 3–5 sentences)

Q4. What are d- and f-block elements? Mention their positions in the periodic table.
Ans:

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Q5. Why do transition metals have high melting and boiling points?
Ans:

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Q6. Write any three physical properties of transition elements.
Ans:

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Section C: Conceptual Questions

(Think and answer in detail)

Q7. Explain why Cr has a configuration of 3d⁵ 4s¹ instead of 3d⁴ 4s².
Ans:

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Q8. What is lanthanoid contraction? What causes it?
Ans:

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