CBSE 2025, Set 3

Question

Give reasons for the following:

(I) Transition metals exhibit catalytic properties.

(II) Transition metals have high enthalpy of atomisation.

(III) Sc is a transition element, while Zn is not.

Edvaya · Accepted Answer

The correct answer is Subjective. **(I) Transition metals as catalysts:** Transition metals are good catalysts because: - They have the ability to **exhibit variable oxidation states** (partially filled d-orbitals) — they can easily gain and lose electrons, acting as electron donors/acceptors in reaction intermediates. - They have a **tendency to form complex compounds** (coordination compounds) that can activate bonds in reactant molecules. - They have **large surface areas** (in finely divided state) which provide active sites for adsorption of reactant molecules (heterogeneous catalysis). **(II) High enthalpy of atomisation:** Transition metals have **high enthalpy of atomisation** because they have **strong metallic bonds** in the solid state. This is due to the involvement of **(n–1)d electrons** as well as **ns electrons** in metallic bonding. The large number of unpaired d electrons available for metallic bonding results in strong interatomic interactions and high energy required to convert solid metal to gaseous atoms. **(III) Sc is a transition element; Zn is not:** **IUPAC definition:** A transition element has **at least one ion with an incompletely filled d-subshell**. - **Sc (Z=21):** [Ar]3d$^1$4s$^2$. Sc$^{3+}$: [Ar] (d$^0$). However, Sc in its **ground state** has an incompletely filled d$^1$ orbital → Sc IS a transition element. (Note: Some definitions accept ground state configuration.) - **Zn (Z=30):** [Ar]3d$^{10}$4s$^2$. Zn$^{2+}$: [Ar]3d$^{10}$ — **completely filled d$^{10}$** in both ground state and all oxidised states. Zn has no ion with partially filled d-orbitals → Zn is **not** a transition element.

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Chemistry > Inorganic Chemistry > D And F Block Elements

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