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JEE MainChemistryClassification of Elements and Periodicity in Properties

The first ionization enthalpy of Gallium (Ga) is higher than that of Aluminum (Al). The primary reason for this observation is :

Options

  1. Athe poor shielding effect of inner 3d-electrons in Gallium leading to a higher effective nuclear charge.
  2. Bthe high shielding effect of inner 3d-electrons in Gallium leading to a lower effective nuclear charge.
  3. Cthe greater atomic size of Gallium compared to Aluminum.
  4. Dthe inert pair effect which strongly binds the valence s-electrons in Gallium.

Correct answer

A. the poor shielding effect of inner 3d-electrons in Gallium leading to a higher effective nuclear charge.

Step-by-step solution

Gallium (atomic number 31) is preceded by the 3d transition series. The 10 inner 3d-electrons provide poor shielding for the outer valence electrons against the increasing nuclear charge. As a result, the effective nuclear charge ( Z_ eff ) experienced by the valence electrons in Gallium is higher than expected. This makes it harder to remove an electron, resulting in a higher first ionization enthalpy for Gallium compared to Aluminum. Answer: the poor shielding effect of inner 3d-electrons in Gallium leading to a

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