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Periodic Table and Periodicity question

2020 · 3 Sep · Shift 2 · Q13
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Periodic Table and Periodicity question

2020 · 3 Sep · Shift 2 · Q13

JEE MainChemistryPeriodic Table and PeriodicityMCQ+4 / −1
The five successive ionization enthalpies of an element are 800, 2427, 3658, 25024 and 32824 kJ mol–1. The number of valence electrons in the element is :
  1. A
    2
  2. B
    3
  3. C
    4
  4. D
    5
View written solutionFree

Correct answer: B

  1. Write the given successive ionization enthalpies

    \quad I_2 = 2427, \quad I_3 = 3658, \quad I_4 = 25024, \quad I_5 = 32824\ \text{kJ mol}^{-1}$$

  2. Use the ionization enthalpy jump rule

    A very large jump between two successive ionization enthalpies indicates that after removing a certain number of electrons, the next electron is being removed from an inner shell.

    Therefore, the number of electrons removed before the large jump equals the number of valence electrons.

  3. Check the differences

    I2−I1=2427−800=1627I_2 - I_1 = 2427 - 800 = 1627I2​−I1​=2427−800=1627 I3−I2=3658−2427=1231I_3 - I_2 = 3658 - 2427 = 1231I3​−I2​=3658−2427=1231 I4−I3=25024−3658=21366I_4 - I_3 = 25024 - 3658 = 21366I4​−I3​=25024−3658=21366 I5−I4=32824−25024=7800I_5 - I_4 = 32824 - 25024 = 7800I5​−I4​=32824−25024=7800

    The largest jump is from I3I_3I3​ to I4I_4I4​.

  4. Interpretation

    This means the first 3 electrons are valence electrons and are removed relatively more easily.

    The 4th electron belongs to an inner shell, so removing it requires a huge amount of energy.

    Hence, the element has:

    3 valence electrons\boxed{3 \text{ valence electrons}}3 valence electrons​

  5. Match with options

    Option B: 3 is correct.

  6. Comparison with stored answer

    Stored correct answer: B

    Derived answer: B

    So, they agree.

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