NCERT Class 12 Chemistry Chemistry-I: Chapter 4 — The d- and f-Block Elements
This chapter introduces the d- and f-block elements, also known as transition and inner transition metals, respectively. It covers their positions in the periodic table, electronic configurations, and general characteristics. The chapter highlights the importance of these elements in human civilization and modern technology, citing examples like iron, copper, gold, and radioactive elements. It explains the IUPAC definition of transition metals based on incomplete d-subshells and discusses exceptions like zinc, cadmium, and mercury. The text details the four series of transition metals (3d, 4d, 5d, 6d) and the two series of inner transition metals (lanthanoids and actinoids). It delves into the electronic configurations of d-block elements, noting exceptions due to the stability of half-filled and completely filled orbitals, such as in Chromium and Copper. The chapter aims to provide a comprehensive understanding of these elements and their compounds, preparing students for advanced chemistry concepts.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 12 |
| Subject | Chemistry |
| Book | Chemistry-I |
| Chapter | Chapter 4 — The d- and f-Block Elements |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 5 minutes |
| Word count | 801 |
Learning outcomes
- Learn the positions of d- and f-block elements in the periodic table.
- Know the electronic configurations of transition (d-block) and inner transition (f-block) elements.
- Appreciate the relative stability of various oxidation states using electrode potential values.
- Describe the preparation, properties, structures, and uses of important compounds like K2Cr2O7 and KMnO4.
- Understand the general characteristics and trends in properties of d- and f-block elements.
- Compare lanthanoids and actinoids based on electronic configurations, oxidation states, and chemical behavior.
Vocabulary
| Word | Meaning |
|---|---|
| Transition elements | Metals with incomplete d subshell either in neutral atom or in their ions. |
| Inner transition elements | Elements in which 4f and 5f orbitals are progressively filled. |
| Lanthanoids | The 4f series of inner transition metals (Ce to Lu). |
| Actinoids | The 5f series of inner transition metals (Th to Lr). |
| Electronic configuration | The arrangement of electrons in atomic orbitals. |
| Oxidation states | The degree of oxidation of an atom in a chemical compound. |
| Penultimate energy level | The second to last electron shell in an atom. |
| Ground state | The lowest possible energy state of an atom or molecule. |
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Practice questions
- What defines transition metals according to IUPAC? Answer: Transition metals are defined as metals which have incomplete d subshell either in a neutral atom or in their ions.
- Name the four series of transition metals. Answer: The four series are 3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La and Hf to Hg), and 6d series (Ac and elements from Rf to Cn).
- Why are zinc, cadmium, and mercury not considered transition metals? Answer: They have a full d10 configuration in their ground state and common oxidation states, thus not meeting the IUPAC definition of transition metals.
- What are lanthanoids and actinoids? Answer: Lanthanoids are the 4f series of inner transition metals, and actinoids are the 5f series.
- Give an example of an exception in the electronic configuration of transition elements and explain why. Answer: Chromium (Cr) has the configuration 3d5 4s1 instead of 3d4 4s2. This is because a half-filled d-subshell (3d5) is more stable.
Practice MCQs
Q1. Which of the following elements is NOT considered a transition metal by IUPAC definition?
Explanation: Zinc (Zn) has a complete d10 configuration in its ground state and common oxidation states, thus it is not classified as a transition metal by IUPAC.
Q2. The 4f series of inner transition metals is known as:
Explanation: The 4f series, ranging from Cerium (Ce) to Lutetium (Lu), is known as the lanthanoids.
Q3. The general electronic configuration of outer orbitals of d-block elements is:
Explanation: The d-orbitals belong to the penultimate energy level (n-1), and the outermost s orbital belongs to the valence shell (ns).
Q4. Which element in the 3d series has the electronic configuration 3d5 4s1?
Explanation: Chromium (Cr) exhibits an exceptional electronic configuration of 3d5 4s1 due to the enhanced stability of a half-filled d-subshell.
Q5. The f-block elements are placed in a separate panel at the bottom of the periodic table because:
Explanation: The f-block elements are characterized by the filling of 4f and 5f orbitals, which necessitates their placement in a separate section for clarity.
Q6. Which of the following is an example of an industrially important transition metal?
Explanation: Iron (Fe) is a crucial industrially important transition metal, widely used in construction, manufacturing, and various other applications.
Frequently asked questions
What are the d-block and f-block elements?
The d-block elements are those in which the d orbitals are progressively filled, typically groups 3-12. The f-block elements are those in which 4f and 5f orbitals are progressively filled, placed separately at the bottom of the periodic table.
Are zinc, cadmium, and mercury transition metals?
According to the IUPAC definition, zinc, cadmium, and mercury are not considered transition metals because they have a complete d10 electron configuration in their neutral atoms and common ions.
What is the main difference between lanthanoids and actinoids?
Lanthanoids involve the filling of 4f orbitals, while actinoids involve the filling of 5f orbitals. Actinoids are also generally radioactive.
Why are some electronic configurations of transition elements exceptions to the general rule?
Exceptions like Cr (3d5 4s1) and Cu (3d10 4s1) occur because half-filled (d5) and completely-filled (d10) d-orbitals have extra stability, making these configurations energetically favorable.
What are some important compounds of transition metals discussed in this chapter?
The chapter focuses on important compounds like Potassium dichromate (K2Cr2O7) and Potassium permanganate (KMnO4), discussing their preparation, properties, and uses.
How do transition elements differ from non-transition elements?
Transition elements are distinguished by the presence of partly filled d or f orbitals in their atoms, which leads to unique chemical properties compared to non-transition elements.
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NCERT Class 12 Chemistry — Chemistry-I — Chapter 4 — The d- and f-Block Elements. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.