What is the characteristic configuration of f-block elements?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Detailed Solution

🔵 Step 1: What are f-block elements?

The f-block elements are those elements in which the differentiating electron enters the (n−2)f subshell. They are placed separately at the bottom of the periodic table.

Differentiating electron → (n−2)f subshell

🟢 Step 2: General Electronic Configuration

The general or characteristic electronic configuration of f-block elements is:

(n−2)f^1–14(n−1)d^0–1ns²

Here, the (n−2)f subshell is progressively filled from one element to the next.

f¹ f² f³ → f¹⁴

🟣 Two Series of f-Block Elements

Series	Subshell Being Filled	Period
Lanthanoids	4f	6th
Actinoids	5f	7th

Lanthanoids → 4f^1–14
Actinoids → 5f^1–14

🎬 f-Orbital Filling

(n−2)f^1–14

f¹ f² f³ ... f¹⁴

↓

🎯 f-subshell is progressively filled

🟠 Important Examples

Lanthanoids: Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu

Actinoids: Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr

The f-block elements are also called inner transition elements.

✅ Final Answer

The characteristic electronic configuration of f-block elements is:

(n−2)f^1–14(n−1)d^0–1ns²

The differentiating electron enters the (n−2)f subshell.

📝 20 MCQs with Answers

1. What is the characteristic configuration of f-block elements?

A) ns¹

B) ns²np⁶

C) (n−2)f¹⁻¹⁴(n−1)d⁰⁻¹ns²

D) (n−1)d¹⁻¹⁰ns²

✅ Answer

C) (n−2)f¹⁻¹⁴(n−1)d⁰⁻¹ns²

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2. In f-block elements, the differentiating electron enters the:

A) ns orbital

B) np orbital

C) (n−1)d orbital

D) (n−2)f orbital

✅ Answer

D) (n−2)f orbital

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3. f-block elements are also known as:

A) Representative elements

B) Inner transition elements

C) Noble gases

D) Halogens

✅ Answer

B) Inner transition elements

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4. Lanthanoids involve filling of which subshell?

A) 3d

B) 4f

C) 5d

D) 5f

✅ Answer

B) 4f

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5. Actinoids involve filling of which subshell?

A) 4f

B) 4d

C) 5f

D) 6d

✅ Answer

C) 5f

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6. How many electrons can an f-subshell accommodate?

A) 2

B) 6

C) 10

D) 14

✅ Answer

D) 14

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7. Lanthanoids belong mainly to the:

A) 4th period

B) 5th period

C) 6th period

D) 7th period

✅ Answer

C) 6th period

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8. Actinoids belong mainly to the:

A) 5th period

B) 6th period

C) 7th period

D) 4th period

✅ Answer

C) 7th period

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9. Which of the following is a lanthanoid?

A) U

B) Ce

C) Th

D) Ac

✅ Answer

B) Ce

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10. Which of the following is an actinoid?

A) La

B) Ce

C) U

D) Eu

✅ Answer

C) U

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11. The f-block is placed separately at the:

A) Top of periodic table

B) Bottom of periodic table

C) Centre of periodic table

D) Right side only

✅ Answer

B) Bottom of periodic table

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12. The maximum number of electrons in f-subshell is:

A) 6

B) 10

C) 14

D) 18

✅ Answer

C) 14

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13. General configuration of lanthanoids involves:

A) 3f

B) 4f

C) 5f

D) 6f

✅ Answer

B) 4f

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14. General configuration of actinoids involves:

A) 3f

B) 4f

C) 5f

D) 6f

✅ Answer

C) 5f

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15. Which series contains uranium?

A) Lanthanoids

B) Actinoids

C) Transition elements

D) Halogens

✅ Answer

B) Actinoids

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16. Which series contains europium?

A) Actinoids

B) Lanthanoids

C) Transition elements

D) Alkali metals

✅ Answer

B) Lanthanoids

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17. f-block elements are mainly:

A) Metals

B) Non-metals

C) Noble gases

D) Metalloids

✅ Answer

A) Metals

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18. The f-block contains:

A) Only lanthanoids

B) Only actinoids

C) Lanthanoids and actinoids

D) Halogens

✅ Answer

C) Lanthanoids and actinoids

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19. The f-subshell has how many orbitals?

A) 3

B) 5

C) 7

D) 9

✅ Answer

C) 7

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20. Each f-orbital can accommodate:

A) 1 electron

B) 2 electrons

C) 4 electrons

D) 6 electrons

✅ Answer

B) 2 electrons

Q1. Write the general electronic configuration of f-block elements.

Solution:

(n−2)f^1–14(n−1)d^0–1ns²

Q2. Which subshell is progressively filled in f-block elements?

Solution: The (n−2)f subshell is progressively filled.

Q1. Explain the characteristic configuration of f-block elements.

Solution:

1. The differentiating electron enters the (n−2)f subshell.
2. The general configuration is (n−2)f¹⁻¹⁴(n−1)d⁰⁻¹ns².
3. They include the lanthanoids and actinoids.

Q1. Differentiate between lanthanoids and actinoids on the basis of electronic configuration.

Feature	Lanthanoids	Actinoids
Subshell filled	4f	5f
Period	6th	7th
General filling	4f¹⁻¹⁴	5f¹⁻¹⁴

Q1. Explain the position and electronic configuration of f-block elements.

Solution:

• f-block elements are placed separately at the bottom of the periodic table.
• They are called inner transition elements.
• The differentiating electron enters the (n−2)f subshell.
• Their general configuration is (n−2)f¹⁻¹⁴(n−1)d⁰⁻¹ns².
• They are divided into lanthanoids (4f) and actinoids (5f).

f-block → (n−2)f¹⁻¹⁴(n−1)d⁰⁻¹ns²

Q1. Explain in detail the characteristic electronic configuration of f-block elements and their two series.

Solution:

The f-block elements are those in which the differentiating electron enters the (n−2)f subshell. They are known as inner transition elements and are placed separately at the bottom of the periodic table.

(n−2)f^1–14(n−1)d^0–1ns²

There are two series:

Series	Subshell Filled	Period
Lanthanoids	4f¹⁻¹⁴	6th
Actinoids	5f¹⁻¹⁴	7th

The f-subshell contains seven orbitals and can accommodate a maximum of 14 electrons. Therefore, the f-block configuration is represented by f¹ to f¹⁴.

🎯 Final Answer:

Characteristic configuration of f-block elements:

(n−2)f^1–14(n−1)d^0–1ns²

The differentiating electron enters the (n−2)f subshell.

🎯 Quick Revision

f-block → Inner Transition Elements
General Configuration → (n−2)f¹⁻¹⁴(n−1)d⁰⁻¹ns²
Differentiating Electron → (n−2)f
Lanthanoids → 4f
Actinoids → 5f
Maximum f-electrons → 14