Ionisation enthalpies of Ce, Pr and Nd are higher than Th, Pa and U. Why?
For Th, Pa and U, 5f electrons start filling and they have lower penetration than 4f electrons for Ce, Pr and Nd. Removal of weakly bound 5f electrons is easier than removing 4f electrons, so ionization enthalpy for Th, Pa and U is lower than Ce, Pr and Nd.
The 5f electrons will therefore, be more effectively shielded from the nuclear charge than 4f electrons of the corresponding lanthanoids. Therefore, outer electrons are less firmly held and they are available for bonding in the actinoids.
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Mention the type of compounds formed when small atoms like H, C and N gettrapped inside the crystal lattice of transition metals. Also give physical and chemical characteristics of these compounds.Chemistry - Exemplar
(a) Answer the following questions :
(i) Which element of the first transition series has highest second ionization enthalpy?
(ii) Which element of the first transition series has highest third ionization enthalpy?
(iii) Which element of the first transition series has lowest enthalpy of atomisation?
(b) Identify the metal and justify your answer.
(i) Carbonyl M (CO)5
Chemistry - Exemplar
When a chromite ore (A) is fused with sodium carbonate in free excess of air and the product is dissolved in water, a yellow solution of compound (B) is obtained. After treatment of this yellow solution with sulphuric acid, compound (C) can be crystallised from the solution. When compound (C) is treated with KCl solution, orange crystals of compound (D) crystallise out. Identify compounds A to D and also explain the reactions.
An oxide of mangnese (A) is fused with KOH in the presence of an oxidizing agent and dissolved in water. A dark green solution of compound (B) is obtained. Compound (B) disproportionates in neutral or acidic solution to give purple compound (C). Alkaline solution of (C) oxidises potassium iodide solution to a compound (D) and compound (A) is also formed. Identify compounds A to D and also explain the reactions involved.
Chemistry - Exemplar