Chemistry Notes for Chapter 4 The D and F Block Elements Class 12 - FREE PDF Download
Vedantu offers Class 12 Chemistry Chapter 4: D and F Block Elements notes that simplify the complex properties and trends of these elements. These notes cover the d-block elements (transition metals) and f-block elements (lanthanoids and actinoids), explaining their electronic configurations, oxidation states, and industrial applications. Students can use these notes for better understanding and quick revision of important concepts before exams. Download the FREE PDF of these notes from Vedantu for a comprehensive study experience and thorough exam preparation.
Table of Content
Class 12 Chapter 4 D and F Block Elements lets you quickly access and review the chapter content. For a comprehensive study experience, check out the Class 12 Chemistry Revision Notes FREE PDF here and refer to the CBSE Class 12 Chemistry syllabus for detailed coverage. Vedantu's notes offer a focused, student-friendly approach, setting them apart from other resources and providing you with the best tools for success.
FAQs on The D and F Block Elements Class 12 Chemistry Chapter 4 CBSE Notes - 2025-26
1. What are the key concepts to focus on for a quick revision of the D and F Block Elements chapter?
For a quick summary as per the CBSE 2025-26 syllabus, focus on these core areas:
- Electronic configurations of the d- and f-block elements and their common exceptions.
- Trends in fundamental properties like atomic radii, ionisation enthalpy, and oxidation states.
- The reasons behind characteristic properties such as forming coloured ions, magnetic behaviour, and catalytic activity.
- The concept and major consequences of Lanthanoid Contraction.
- A clear comparison between the properties of Lanthanoids and Actinoids.
2. How do transition metals (d-block) fundamentally differ from inner transition metals (f-block) in a quick summary?
The main difference lies in the orbital where the differentiating electron enters. In transition metals, the last electron enters the (n-1)d orbital, while in inner transition metals, it enters the (n-2)f orbital. This leads to key differences: d-block elements show more variable oxidation states and form complexes more readily, while f-block elements are characterized by the Lanthanoid Contraction and have more similar chemical properties across their series.
3. What is the core conceptual link between the formation of coloured ions and the magnetic properties of transition metals?
The conceptual link is the presence of unpaired electrons in the d-orbitals. The d-d transition, where these electrons absorb energy from visible light to get excited to a higher energy d-orbital, is responsible for the coloured nature of their compounds. This same presence of unpaired electrons causes the substance to be attracted to a magnetic field, resulting in paramagnetism. Therefore, both properties originate from the same source: a partially filled d-subshell.
4. Why is understanding Lanthanoid Contraction crucial when revising the f-block elements?
Lanthanoid Contraction is crucial because it explains a key periodic trend. It refers to the steady decrease in the size of lanthanoid atoms and ions with increasing atomic number due to poor shielding by f-electrons. Its most important consequence is that the atomic radii of the elements in the second (4d) and third (5d) transition series become almost identical. This similarity in size leads to great similarity in their chemical properties, making their chemical separation very difficult.
5. Why do transition elements exhibit variable oxidation states while s-block elements do not?
Transition elements show variable oxidation states because the energy difference between their (n-1)d and ns orbitals is very small. This allows electrons from both subshells to participate in chemical bonding. In contrast, s-block elements only have valence electrons in the ns orbital, and removing an electron from the inner, completely filled shell requires a very high amount of energy, making it unfeasible.
6. How does the electronic configuration of transition metals explain their ability to act as good catalysts?
The catalytic activity of transition metals is explained by two key features. Firstly, their ability to exhibit variable oxidation states allows them to form unstable intermediate compounds, creating an alternative reaction pathway with lower activation energy. Secondly, they provide a suitable surface for reactants to adsorb, which increases the local concentration of reactants and weakens their bonds, thus speeding up the reaction.
7. What are some common pitfalls to avoid when revising the D and F Block Elements?
When revising this chapter, be careful to avoid these common mistakes:
- Confusing the electronic configurations of exceptions like Chromium (Cr) and Copper (Cu).
- Failing to explain why Zinc (Zn), Cadmium (Cd), and Mercury (Hg) are not considered typical transition elements despite being in the d-block.
- Simply memorising trends without understanding the underlying reasons like shielding effect and increasing nuclear charge.
- Overlooking the significant differences in radioactivity and oxidation states between Lanthanoids and Actinoids.
8. What is the main formula to remember for calculating magnetic properties in this chapter?
The key formula to remember is for calculating the 'spin-only' magnetic moment (μ), which is given by μ = √n(n+2), with the unit Bohr Magneton (BM). In this formula, 'n' represents the number of unpaired electrons. It is essential for correlating the electronic configuration of a transition metal ion with its observed magnetic behaviour.
9. For revision, what is the primary difference in chemical reactivity between Lanthanoids and Actinoids?
The key difference to remember is that Actinoids exhibit a much wider range of oxidation states (e.g., up to +7) compared to Lanthanoids, which primarily show the +3 oxidation state. Additionally, all actinoids are radioactive, which is a defining feature of their chemistry, whereas among lanthanoids, only promethium is radioactive. Actinoids also have a greater tendency to form complexes.
10. Why are most transition metal compounds coloured, while those of s- and p-block elements are typically white?
Most transition metal compounds are coloured due to the presence of partially filled d-orbitals. This allows for the d-d electronic transition, where an electron absorbs energy from the visible light spectrum to jump to a higher energy d-orbital. The compound appears as the complementary colour of the light absorbed. In contrast, s- and p-block elements usually have no unpaired d-electrons, and the energy required to excite their electrons is very high, falling outside the visible spectrum. Thus, they do not absorb visible light and appear white or colourless.
