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प्रश्न
Although \[\ce{Cr^3+}\] and \[\ce{Co^2+}\] ions have same number of unpaired electrons but the magnetic moment of \[\ce{Cr^3+}\] is 3.87 B.M. and that of \[\ce{Co^2+}\] is 4.87 B.M. Why?
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उत्तर
Magnetic moment of an electron/dipole moment is caused by its intrinsic properties of spin and electric charge. It depends upon the number of unpaired electrons in its valence shell. The more the number of unpaired electrons, the greater will be the value of magnetic moment.
\[\ce{Cr^{3+} = [Ar] 3d^3 = 3 unpaired electrons}\]
\[\ce{Co^{2+} = [Ar] 3d^7 = 3 unpaired electrons}\]
But as both the ions have the same no. of unpaired electrons, there’s one other factor called orbital contribution which also influences the magnetic moment. As, the three unpaired electronic configurations is symmetrical in \[\ce{Cr^3+}\] this contributes zero orbital contribution but this is quite appreciable in case of \[\ce{Co^2+}\] and hence it has larger value of Magnetic moment than \[\ce{Cr^3+}\].
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संबंधित प्रश्न
Out of Mn3+ and Cr3+, which is more paramagnetic and why ?
(Atomic nos. : Mn = 25, Cr = 24)
Calculate the ‘spin only’ magnetic moment of \[\ce{M^{2+}_{( aq)}}\] ion (Z = 27).
Describe the oxidising action of potassium dichromate and write the ionic equation for its reaction with iodide.
For M2+/M and M3+/M2+ systems, the E° values for some metals are as follows:
| Cr2+/Cr | −0.9 V |
| Mn2+/Mn | −1.2 V |
| Fe2+/Fe | −0.4 V |
| Cr3/Cr2+ | −0.4 V |
| Mn3+/Mn2+ | +1.5 V |
| Fe3+/Fe2+ | +0.8 V |
Use this data to comment upon:
- The stability of Fe3+ in acid solution as compared to that of Cr3+ or Mn3+ and
- the ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.
Predict which of the following will be coloured in the aqueous solution?
Ti3+, V3+, Cu+, Sc3+, Mn2+, Fe3+ and Co2+. Give reasons for each.
Comment on the statement that elements of the first transition series possess many properties different from those of heavier transition elements.
Complete and balance the following chemical equations
`MnO_4^(-) + H_2O + I^(-) ->`
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.
A solution of \[\ce{KMnO4}\] on reduction yields either a colourless solution or a brown precipitate or a green solution depending on pH of the solution. What different stages of the reduction do these represent and how are they carried out?
While filling up of electrons in the atomic orbitals, the 4s orbital is filled before the 3d orbital but reverse happens during the ionisation of the atom. Explain 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.
Which of the following is non-metallic?
Mercury is the only metal liquid at room temperature due to its:-
On adding NaOH, solution to the aqueous solution of K2CrO7 the colour of the solution changes from
The oxidation state of Fe in [Fe(CO)5] is ______.
Assertion (A): Transition metals have high enthalpy of atomisation.
Reason (R): Greater number of unpaired electrons in transition metals results in weak metallic bonding.
The given graph shows the trends in melting points of transition metals:
Explain the reason why Cr has the highest melting point and manganese (Mn) has a lower melting point.
Consider the following standard electrode potential values:
\[\ce{Fe^{3+}_{ (aq)} + e^- -> Fe^{2+}_{ (aq)}}\], E0 = +0.77 V
\[\ce{MnO^{-4}_{ (aq)} + 8H^+ + 5e^- -> Mn^{2+}_{ (aq)} + 4H2O_{(l)}}\], E0 = +1.51 V
What is the cell potential for the redox reaction?
For M2+/M and M3+/M2+systems, the EΘ values for some metals are as follows:
| Cr2+/Cr | −0.9 V |
| Mn2+/Mn | −1.2 V |
| Fe2+/Fe | −0.4 V |
| Cr3/Cr2+ | −0.4 V |
| Mn3+/Mn2+ | +1.5 V |
| Fe3+/Fe2+ | +0.8 V |
Use this data to comment upon:
The ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.
Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following point:
Atomic sizes
