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प्रश्न
Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?
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उत्तर १
The oxidation states displayed by the first half of the first row of transition metals are given in the table below.
| Sc | Ti | V | Cr | Mn | Fe | Co | Ni | Cu | Zn |
| +2 | +2 | +2 | +2 | +2 | +2 | +2 | +1 | +2 | |
| +3 | +3 | +3 | +3 | +3 | +3 | +3 | +3 | +2 | |
| +4 | +4 | +4 | +4 | +4 | +4 | +4 | |||
| +5 | +5 | +5 | |||||||
| +6 | +6 | +6 | |||||||
| +7 |
It can be easily observed that except Sc, all other metals display +2 oxidation states. Also, on moving from Sc to Mn, the atomic number increases from 21 to 25. This means the number of electrons in the 3d-orbital also increases from 1 to 5.
| Sc (+2) = d1 |
| Ti (+2) = d2 |
| V (+2) = d3 |
| Cr (+2) = d4 |
| Mn (+2) = d5 |
+2 oxidation state is attained by the loss of the two 4s electrons by these metals. Since the number of d electrons in (+2) state also increases from Ti (+2) to Mn (+2), the stability of +2 state increases (as d-orbital is becoming more and more half-filled). Mn (+2) has d5 electrons (that is, a half-filled d shell, which is highly stable).
उत्तर २
Losing two electrons from s-orbital leads to an increase in effective nuclear charge as the atomic number increases. The ion size decreases, which leads to more stability. The stability is reduced in the beginning because there are few electrons to lose or exchange.
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संबंधित प्रश्न
Account for the following:
Mn shows the highest oxidation state of +7 with oxygen but with fluorine, it shows oxidation state of +4.
Account for the following:
Zn is not considered as a transition element.
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How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.
What can be inferred from the magnetic moment value of the following complex species?
| Example | Magnetic Moment (BM) |
| K2[MnCl4] | 5.9 |
Write the formula of an oxo-anion of Chromium (Cr) in which it shows the oxidation state equal to its group number
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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.
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: Crystal structure of oxides of transition metals often show defects.
Reason: Ligand field effect cause distortions in crystal structures.
Transition elements show magnetic moment due to spin and orbital motion of electrons. Which of the following metallic ions have almost same spin only magnetic moment?
(i) \[\ce{Co^{2+}}\]
(ii) \[\ce{Cr^{2+}}\]
(iii) \[\ce{Mn^{2+}}\]
(iv) \[\ce{Cr^{3+}}\]
Catalytic hydrogenation of benzene gives
Which of the following statements is not correct?
Which of the following transition metal is not coloured?
The number of terminal oxygen atoms present in the product B obtained from the following reactions is:
\[\ce{FeCr2O4 + Na2CO3 + O2 -> A + Fe2O3 + CO2}\]
\[\ce{A + H^+ -> B + H2O + Na^+}\]
Assertion (A): Transition metals have high enthalpy of atomisation.
Reason (R): Greater number of unpaired electrons in transition metals results in weak metallic bonding.
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Oxidation states
The E° value for the Mn2+/Mn2+ couple is more positive than that of Cr3+/Cr2+ or Fe3+/Fe2+ due to the change of:
