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In the series Sc(Z=21) to Zn(Z=30) the e...

In the series `Sc(Z=21)` to `Zn(Z=30)` the enthalpy of atomisation of zinc is the lowest, i.e., 126 kJ `mol^(-1)`. Why?

Text Solution

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In the series , Sc to Zn , all elements have one or more unpaired electrons except zinc which has no unpaired electron as its outer electronic configuration is `3d^(10)4s^(2)`. Hence, atomic intermetallic bonding ( metal - metal bonding) is weakest in zinc. Therefore, enthalpy of atomisation is lowest.
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In 3d series, the enthalpy of atomisation of zinc is the lowest Why?

Read the given passage and answer the questions number 1 to 5 that follow : The lowest common oxidation state of transition metals is + 2. To form the M^(2+) ions from the gaseous atoms, the sum of the first and second ionisation enthalpy is required in addition to the enthsualpy of atomisation. The dominant term is the second ionisation enthalpy which shows unusually high values for Cr and Cu where M^(+) ions have the d^(5) and d^(10) configurations respectively. The value for Zn is correspondingly low as the ionisation causes the removal of 1s electron which results in the formation of stable d^(10) configuration. The trend in the third ionisation enthalpies is not complicated by the 4s orbital factor and shows the greater difficulty of removing an electron from the d^(5) (Mn^(2+)) and d^(10) (Zn^(2+)) ions. In general, the third ionisation enthalpies are quite high. Also, the high values for third ionisation enthalpies of copper, nickel and zinc indicate why it is difficult to obtain oxidation state greater than two for these elements. In the series Sc(Z = 21) to Zn(Z = 30), the enthalpy of atomisation of Zn is the lowest. Why?

Knowledge Check

  • In the series Sc (2 = 21) to Zn (Z=30), the enthalpy of atomisation of which element is least?

    A
    Sc
    B
    Mn
    C
    Cu
    D
    Zn

  • Assertion : In the series Sc to Zn, the enthalpy of atomisation of zinc is the lowest. Reason : Zinc has greater number of unpaired electrons.

    A
    If both assertion and reason are true and reason is the correct explanation of assertion.
    B
    If both assertion and reason are true and reason not is the correct explanation of assertion.
    C
    If assertion is trun but reason is false.
    D
    If both assertion and reason are false.

  • Bond dissociation enthalpies of H_(2(g)) and N_(2(g)) are "426.0 kJ mol"^(-1) and "941.8 kJ mol"^(-1) , respectively, and enthalpy of formation of NH_(3(g))" is "-"46 kJ mol"^(-1) . What are the enthalpy of atomisation of NH_(3(g)) and the average bond enthalpy of N-H bond respectively ( in kJ "mol"^(-1) )?

    A
    1170.9, 390.3
    B
    117, 300
    C
    300, 200
    D
    2000, 1975

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