Class 12 Chemistry Revision Notes for Chapter 8 - The d and f Block Elements - Free PDF Download
FAQs on D and F Block Elements Class 12 Notes CBSE Chemistry Chapter 8 [Free PDF Download]
1. Explain the Features of d-block Elements?
The general electronic configuration of the d-block elements is given by (n −1) d1-10 ns1-2, where (n −1) stands for the inner d orbitals
In the d-block, each horizontal row consists of 10 elements as d-subshell, and it can accommodate a maximum of 10 electrons
The d-block elements with the incompletely filled d-subshell are known as transition metals
2. Give the Characteristics of Actinoids and Lanthanoids?
Lanthanoids are silvery-white soft metals which tarnish readily when they are exposed to air
The hardness of the lanthanoids increases with an increase in the atomic number
The melting point and boiling point of actinoids are moderately high, but they are considerably lower to that of transition elements
3. Explain the Characteristics of f Block Elements?
In general, these elements have a higher melting point and boiling point
These are usually heavy metals
They are the elements that tend to form coloured ions
They also display a variety of oxidisation states
They can form complex compounds
4. What are the transition elements? Write 3 characteristics of the transition elements.
Elements whose d-orbital is partially filled in the ground states or in any one of the oxidation states of the element are known as transition elements. Their characteristics are:
Showing variable states of oxidation.
Forming coloured ions.
Forming complex compounds.
5. What is lanthanoid contraction?
The all-around decrease in the atomic, as well as ionic radii with an increase in the atomic number, is referred to as lanthanoid contraction. While increasing from La+3 to Lu+3 in a lanthanoid series, the size of the ion reduces. This reduction in the size in the series is called the lanthanoid contraction. This phenomenon arises because of the imperfect shielding of a 4f electron by a different election from the same subshell.
6. Mention the main consequences of lanthanoid contraction.
The similarity of properties because of the lanthanoid contraction, size of elements following (Hf – Hg) become very similar to the size of the previous row elements (Zr – Cd) and therefore they become difficult to make out. Because of small changes in the atomic radii, the properties of lanthanoids are also almost similar making separation very difficult.
Basicity difference is because of the lanthanoid contraction, where size reduces from La+3 to Lu+3. Therefore the covalent character improves. Thus, the basic characteristic of the hydroxides also reduces i.e. the reason La(OH)3 has the highest basicity while Lu(OH)3 has the least.
7. What is meant by ‘’disproportionation’?
In a given reaction, when the oxidation of any element in the compound grows in one product and reduces in another product, the reaction is considered to have undergone a disproportionation of the oxidation state. In simpler words, disproportionation is the reaction wherein a given element undergoes self-oxidation as well as self-reduction at the same time.
8. Why do transition elements show variable oxidation states?
Transition elements show variable oxidation states because there is very little energy difference among the (n-1) d-orbital and ns-orbital. Because of this little energy difference between the orbitals, both the energy levels may be used to form a bond. Therefore transition elements may exhibit a variety of oxidation states.