The d-And-f-Block Elements

  • Question 1
    CBSEENCH12006973

    Silver atom has a completely filled d orbitals (4d10) in its ground state. How can you say that it is a transition element?

    Solution
    Ag has a completely filled 4d orbital (4d10 5s1) in its ground state. Now, silver displays two oxidation states (+1 and +2). In the +1 oxidation state, an electron is removed from the s-orbital. However, in the +2 oxidation state, an electron is removed from the d-orbital. Thus, the d-orbital now becomes incomplete (4d9). Hence, it is a transition element. wherein it will have incompletely filled d-orbitals (4d), hence a transition metal.
    Question 2
    CBSEENCH12006974

    In the series Sc (Z = 21) to Zn(Z = 30), the enthalpy of atomisation of zinc is the lowest i.e., 26, kJ mol. Why?

    Solution
    The extent of metallic bonding an element undergoes deideds the enthalpy of atomization the more extensive the metallic bonding of an element the more will be its enthalpy of atomization.

    Sc & Zn belongs to 3
    rd group of periodic table. In all transition metals (except Zn, electronic configuration: 3d10 4s2), there are some unpaired electrons that account for their stronger metallic bonding. Due to the absence of these unpaired electrons, the inter-atomic electronic bonding is the weakest in Zn and as a result, it has the least enthalpy of atomization.
    Question 3
    CBSEENCH12006975

    The E° (M2+/M) value for copper is positive (+ 0.34 V). What is possibility the reason for this? 

    Solution
    Copper has high atomisation ΔaH° and low hydration energy  Δhyd H°. Due to which the E° value is positive.
    Question 4
    CBSEENCH12006976

    How would you account for the irregular variation of ionisation enthalpies (first and second) in the first series of the transition elements?

    Solution

    Ionization enthalpies are found to increase in the given series due to a continuous filling of the inner d-orbitals. The irregular variations of ionization enthalpies can be attributed to the extra stability of configurations such as d0, d5, d10. Since these states are exceptionally stable, their ionization enthalpies are very high.

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