(a) What are interstitial Compounds? Give example also. [2]
(b) Write the electronic configuration of the following ions- (i) Cu+ (ii) Ce4+ [2]

OR

Give reasons for the following -
(a) Actinoid contraction is greater from element to element than Lanthanoid contraction. [2]
(b) T

Question

(a) What are interstitial Compounds? Give example also. [2]
(b) Write the electronic configuration of the following ions- (i) Cu+ (ii) Ce4+ [2]

OR

Give reasons for the following -
(a) Actinoid contraction is greater from element to element than Lanthanoid contraction. [2]
(b) Transition metals and their many compounds act as good catalyst. [2]

Accepted Answer

>

> [!TLDR]
> Interstitial compounds trap small atoms in the metal lattice; ion configurations follow from removing electrons off the outermost shell first. OR: 5f electrons shield poorly (more actinoid contraction); transition metals catalyse via variable oxidation states and d-orbital adsorption.
>
> **(a) Interstitial compounds:** These are compounds formed when small atoms such as hydrogen, carbon, nitrogen or boron get trapped inside the empty interstitial spaces (voids) of the crystal lattice of transition metals. They are usually **non-stoichiometric** (not obeying simple laws of definite proportions), retain **metallic conductivity**, are chemically **inert**, very **hard**, and have **higher melting points** than the pure metal. Examples: $TiC$, $Mo_2C$, $Fe_3H$, $TiH_{1.7}$, $Fe_4N$ (iron nitride).
>
> **(b) Electronic configurations:**
>
> (i) $Cu$ ($Z=29$): $[Ar]3d^{10}4s^1$. Removing 1 electron to form $Cu^+$ removes the single $4s$ electron:
>
> $Cu^+$: $[Ar]3d^{10}$, i.e. $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10}$
>
> (ii) $Ce$ ($Z=58$): $[Xe]4f^15d^16s^2$. Removing 4 electrons to form $Ce^{4+}$ removes the $6s^2$, $5d^1$ and $4f^1$ electrons:
>
> $Ce^{4+}$: $[Xe]$, i.e. $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 5s^2 5p^6$
>
> ---
>
> **OR:**
>
> **(a) Actinoid contraction > Lanthanoid contraction (per element):** In actinoids, the $5f$ orbitals are being progressively filled, and $5f$ orbitals are more diffuse (larger, more spread out) than the compact $4f$ orbitals of the lanthanoids. Because $5f$ electrons shield the nuclear charge from outer electrons **less effectively** than $4f$ electrons do, the effective nuclear charge experienced by the outer electrons increases more sharply on moving across the actinoid series. This causes a bigger decrease in atomic/ionic radius per element — i.e. **actinoid contraction is greater than lanthanoid contraction** from element to element.
>
> **(b) Transition metals as good catalysts:**
> …

Q.(a) What are interstitial Compounds? Give example also. [2]

Concept understanding — Interstitial Compounds

The Precise Statement

Why They Are Special (and Exam-Relevant)

Q.(a) What are interstitial Compounds? Give example also. [2]

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