CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2011

  • question_answer
    The correct decreasing order of first ionization enthalpies of five elements of the second  period is

    A)  \[Be>B>C>N>F\]

    B)  \[N>F>C>B>Be\]

    C)  \[F>N>C>Be>B\]

    D)  \[N>F>B>C>Be\]

    E)  \[F>C>N>B>Be\]

    Correct Answer: C

    Solution :

    In general, as we move from left to right in a period, the ionization enthalpy increases with increasing atomic numbers. But the ionization enthalpy of B is lower than that of Be. This is because the electronic configuration of \[(1{{s}^{2}}\text{ }2{{s}^{2}}\text{ }2{{p}^{1}})\]is less stable than that of Be \[(1{{s}^{2}}\text{ }2{{s}^{2}})\]which has completely filled orbitals. As a result, the 2p-electron of B is not strongly attracted by the nucleus as the 2s-electron of Be. Thus, the increasing order of first ionization enthalpies of elements is \[F>N>C>Be>B\]


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