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प्रश्न
What are the characteristics of the transition elements and why are they called transition elements?
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उत्तर
- Electronic configuration: General electronic configuration is (n − 1) d1−10ns0−2. This configuration reflects the filling of d-orbitals in addition to the s-orbitals of the outermost shell.
- Metallic character: Transition elements, except for Zn, Cd and Hg, exhibit metallic structures and typical metallic properties like malleability, ductility and conductivity.
- Atomic and ionic size: Across a transition series, the atomic and ionic radii decrease due to the increasing nuclear charge, which pulls the d-electrons closer to the nucleus (a phenomenon called the lanthanide contraction).
- Oxidation state: They exhibit variable oxidation states due to the participation of both d and s-electrons in bonding. Common oxidation states range from +2 to +7, depending on the element.
- Paramagnetism: Ions with unpaired d-electrons exhibit paramagnetism. The greater the number of unpaired electrons, the stronger the paramagnetic behaviour.
- Ionisation enthalpy: Ionisation enthalpy increases gradually across the series as the nuclear charge increases, making it harder to remove electrons.
- Formation of coloured ions: Transition metal ions are often colored because of electronic transitions within the d-orbitals (specifically d-d transitions) when they absorb visible light.
- Formation of complex compounds: Transition metals form complexes due to their small size, high charge density, and availability of vacant d-orbitals to accept electron pairs from ligands.
- They possess catalytic properties: They act as catalysts because they can exist in multiple oxidation states, which facilitates various chemical reactions.
- Formation of interstitial compounds: Transition metals can form interstitial compounds by trapping small non-metal atoms (such as H, C, or N) within their crystal lattice.
- Alloy formation: They readily form alloys due to similar atomic sizes, which allows different metal atoms to substitute for one another in the crystal structure.
They are positioned between s and p-block elements and are known as transition elements because of their incompletely filled d-orbitals in the ground state or any stable oxidation state.
संबंधित प्रश्न
Why is Sc3+ colourless while Ti3+ coloured? (Atomic number Sc = 21, Ti =22)
Why do interstitial compounds have higher melting points than corresponding pure metals?
The elements of 3d transition series are given as: Sc Ti V Cr Mn Fe Co
Answer the following: Which element has the highest m.p?
Explain why Cu+ ion is not stable in aqueous solutions?
What may be the stable oxidation state of the transition element with the following d electron configuration in the ground state of its atom?
3d3
How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.
What is meant by ‘disproportionation’?
How would you account for the following?
Zr (Z = 40) and Hf (Z = 72) have almost identical radii.
An analysis shows that FeO has a non-stoichiometric composition with formula Fe0.95O. Give reason.
Give reasons: Sc3+ is colourless in aqueous solution whereas Ti3+ is coloured.
Explain why transition elements form alloys.
Read the passage given below and answer the following question:
The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since electron bonding levels are involved, the cations exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group.
In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.
Assertion: Cations of transition elements occur in various valence states.
Reason: Large number of oxides of transition elements are possible.
Although Zirconium belongs to 4d transition series and Hafnium to 5d transition series even then they show similar physical and chemical properties because ______.
Transition elements show high melting points. Why?
Assertion: Separation of \[\ce{Zr}\] and \[\ce{Hf}\] is difficult.
Reason: Because \[\ce{Zr}\] and \[\ce{Hf}\] lie in the same group of the periodic table.
When an oxide of manganese (A) is fused with KOH in the presence of an oxidising agent and dissolved in water, it gives a dark green solution of compound (B). Compound (B) disproportionates in neutral or acidic solution to give purple compound (C). An alkaline solution of compound (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.
Give reason for the following statement:
[Ti(H2O)]3+ is coloured while [Sc(H2O)6]3+ is colourless.
Consider the following standard electrode potentials (E° in volts) in aqueous solution:
| Element | M3+/M | M+/M |
| Al | - 1.66 | +0.55 |
| Tl | + 1.26 | -0.34 |
Based on these data, which of the following statements is correct?
In the ground state of atomic Fe (Z = 26), the spin-only magnetic moment is ______ × 10-1 BM.
(Round off to the nearest integer).
[Given: `sqrt3 = 1.73, sqrt2 = 1.41`]
