D And F Tb Flashcards
How would you account for the irregular variation of tonisation enthalpies (first and second) in first series of transition elements
Irregular variation of ionisation enthalpies is mainly attributed to varying degree of stability of different
3d configuration (e.g., d°, d5, d10) are exceptionally stable).
Which is a stronger reducing agent— Cr or Fe’* and why?
(HOTS]
Ans.
Cr’* is a stronger reducing agent than Fe * because after the loss of one electron Cr’* becomes Cr’* which has more stable f2 (half-filled) configuration in a medium like water.
Action is contraction is greater from element to element than lanthanoid contraction
This is because the 5 electrons themselves provide poor shielding from element to element in the series.
Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?
Ans.
As the atomic number increases from 21 to 25, the number of electrons in the 3d-orbital also increases from 1 to 5. +2 oxidation state is attained by the loss of the two 4s electrons by these metals. Sc does not exhibit +2 oxidation state. As the number of d- electrons in +2 state increases from Ti to Mn, the stability of +2 Q. 4.
state increases (d-orbital gradually becoming half filled). Mn(+2) has d’ electrons which is highly stable.
To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with example.
Ans.
The stability of oxidation states in the first series of the transition elements are related to their electronic configurations.
The first five elements of the first transition series up to Mn in which the 3d-subshell is not more than half-filled, the minimum oxidation state is given by the number of electrons in the outer s-subshell and the maximum oxidation state is given by the sum of the outers and d-electrons. For example, Sc does not show +2 oxidation state. Its electronic configuration is 3d’452
. It loses all the three electrons to form Sc3+
. +3 oxidation state is very stable as by losing all three electrons, it attains the stable configuration of Argon. For Mn, +2 oxidation state is very stable, as after losing two 4s electrons, the d-orbitals become half-filled.
Consequences of lanthanoid contraction
The consequences of lanthanoid contraction are as follows:
(i) The properties of second and third transition series are similar.
(ii) Basic strength decreases from La(OH) to Lu(OH)3•
ii) Lanthanide contraction makes separation of lanthanoids possible.
Different os exhibited by lanthanoid
2,3,4
3most common
Transition metals and many of their compounds show paramagnetic behavior
Substances containing unpaired electrons are said to be paramagnetic. A diamagnetic substance is one in which all the electrons are paired. Except the ions of d° (Sc, Tif) and d’° (Cu, Zn?*) configurations, all other simple ions of transition elements contain unpaired electrons in their (n - 1) d subshell and are, therefore, paramagnetic. The magnetic moments (H) of the elements of first transition series can be calculated with the unpaired electrons (n) by the spin only formula.
M=
How is the variability in oxidation states of transition metals diferent from that of the non transiion
metals? Illustrate with examples.
The oxidation states of transition elements differ from each other by unity e.., Fe 2and Fe3+
+, Cu+ and Cu2+
(due to incomplete filling of d-orbitals) whereas oxidation states of non-transition elements normally differ by two units e.g., Pb2+and Pb4+
, Sn2+and Sn4+
Cobalt (II) is stable in aqueous solution but in the presence of complexing reagents it is
easily oxidised.
This is because in presence of complexing reagents the CFSE value compensates more than the third
ionisation energy of cobalt.
The d’ configuration is very unstable in ions.
The ions with d’ configuration have the tendency to lose the only electron present in d-subshell to acquire stable d0 configuration. Therefore, they are unstable and undergo oxidation or disproportionation.
