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Classification of Elements and Periodicity in Properties — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryClassification of Elements and Periodicity in Properties2 Marks
Question
${ }_{31} \mathrm{Ga}$ has slightly higher ionisation enthalpy than ${ }_{13} \mathrm{Al}$ although it occupies lower position in the group?
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Answer

Electronic configuration of ${ }_{13} \mathrm{Al}=1 s^2, 2 s^2, 2 p^6, 3^{52}, 3 p^1$ Electronic configuration of $31 \mathrm{Ga}=1 s^2, 2 s^2, 2 p^6, 3 s^2, 3 p^6, 3 d^{10}$, $4 s^2, 4 p^1$
In $\mathrm{Ga}, 10$ electrons present in 3d-subshell do not shield the outer electrons from the nucleus effectively. As a result, effective nuclear charge in Ga increases. That's why ionisation enthalpy of Ga is slightly more than that of ${ }_{13} \mathrm{Al}$.

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