Explain why actinoid contraction is greater from element to element than lanthanoid contraction.
Show Hint
Solution and Explanation
As we move along the actinoid series, new electrons are added to the \(5f\) subshell. Similarly, in the lanthanoid series, electrons are added to the \(4f\) subshell. The shapes of f-orbitals are highly diffused, meaning they are spread out over a large volume of space. Because they are so diffused, f-electrons are very poor at shielding the outermost valence electrons from the attractive pull of the positive nucleus.
Step 2: Comparing 4f and 5f orbitals.
The \(5f\) orbitals in actinoids are even larger and more diffused (spread out) than the \(4f\) orbitals in lanthanoids. Therefore, the shielding effect of a \(5f\) electron is significantly weaker than that of a \(4f\) electron.
Step 3: Concluding the effect on atomic size.
Due to the poorer shielding provided by the \(5f\) electrons, the effective nuclear charge (\(Z_{\text{eff}}\)) felt by the outermost electrons is much stronger in actinoids compared to lanthanoids. This stronger inward pull by the nucleus results in a more drastic decrease in size (a greater contraction) from one element to the next in the actinoid series. Final Answer: Actinoid contraction is greater than lanthanoid contraction because \(5f\) electrons have a poorer shielding effect than \(4f\) electrons, leading to a stronger effective nuclear charge pulling the valence electrons inward.
Top CBSE CLASS XII Chemistry Questions
- ${AgNO_3}$ does not decompose where :
- Azeotropic mixture of water and HCl boils at 381.5 K. By distilling the mixture it is possible to obtain
Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines.
(i) (CH3 )2CHNH2 (ii) CH3 (CH2 )2NH2 (iii) CH3NHCH(CH3 )2
(iv) (CH3 )3CNH2 (v) C6H5NHCH3 (vi) (CH3CH2 )2NCH3 (vii) m–BrC6H4NH2
Give one chemical test to distinguish between the following pairs of compounds.
(i) Methylamine and dimethylamine
(ii) Secondary and tertiary amines
(iii) Ethylamine and aniline
(iv) Aniline and benzylamine
(v) Aniline and N-methylanilineAccount for the following:
(i) pKb of aniline is more than that of methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not.
(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
(iv) Although amino group is o– and p– directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.
(v) Aniline does not undergo Friedel-Crafts reaction.
(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines. (vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.
Top CBSE CLASS XII Lanthanoids and Actinides Questions
- Calculate \( \Lambda_m^0 \) for acetic acid and its degree of dissociation (\( \alpha \)) if its molar conductivity is 48.1 \( \Omega^{-1} \, \text{cm}^2 \, \text{mol}^{-1} \).
\textbf{Given that
\( \Lambda_m^0 (\text{HC}) = 426 \, \Omega^{-1} \, \text{cm}^2 \, \text{mol}^{-1} \),
\( \Lambda_m^0 (\text{NaCl}) = 126 \, \Omega^{-1} \, \text{cm}^2 \, \text{mol}^{-1} \),
\( \Lambda_m^0 (\text{CH}_3\text{COONa}) = 91 \, \Omega^{-1} \, \text{cm}^2 \, \text{mol}^{-1} \). } - Complete and balance the following chemical equations:
(1) KMnO4 heat →
(2) Cr2O72− + 6 I− + 14 H+ → Calculate \( \Lambda_m^0 \) for acetic acid and its degree of dissociation (\( \alpha \)) if its molar conductivity is 48.1 \( \Omega^{-1} \, \text{cm}^2 \, \text{mol}^{-1} \).
Given that
\( \Lambda_m^0 (\text{HC}) = 426 \, \Omega^{-1} \, \text{cm}^2 \, \text{mol}^{-1} \),
\( \Lambda_m^0 (\text{NaCl}) = 126 \, \Omega^{-1} \, \text{cm}^2 \, \text{mol}^{-1} \),
\( \Lambda_m^0 (\text{CH}_3\text{COONa}) = 91 \, \Omega^{-1} \, \text{cm}^2 \, \text{mol}^{-1} \).
- Assertion (A) : Separation of Zr and Hf is difficult. Reason (R) : Zr and Hf have almost identical atomic and ionic radii due to lanthanoid contraction.
Top CBSE CLASS XII Questions
- 2, b, c are in A.P. and the range of determinant $\begin{vmatrix}1&1&1\\ 2&b&c\\ 4&b^{2}&c^{2}\end{vmatrix}$ is [2, 16]. Then find range of c is
- A boy of mass 50 kg is standing at one end of a, boat of length 9 m and mass 400 kg. He runs to the other, end. The distance through which the centre of mass of the boat boy system moves is
- A capillary tube of radius r is dipped inside a large vessel of water. The mass of water raised above water level is M. If the radius of capillary is doubled, the mass of water inside capillary will be
- A circular disc is rotating about its own axis. An external opposing torque 0.02 Nm is applied on the disc by which it comes rest in 5 seconds. The initial angular momentum of disc is
- A circular disc is rotating about its own axis at uniform angular velocity \(\omega.\) The disc is subjected to uniform angular retardation by which its angular velocity is decreased to \(\frac {\omega}{2}\) during 120 rotations. The number of rotations further made by it before coming to rest is