The first ionization enthalpies of elements X and Y are 419 kJ mol⁻¹ and 590 kJ mol⁻¹, respectively and the se

Question

The first ionization enthalpies of elements X and Y are 419 kJ mol⁻¹ and 590 kJ mol⁻¹, respectively and the second ionization enthalpies of X and Y are 3069 kJ mol⁻¹ and 1145 kJ mol⁻¹, respectively. The correct statement is:

Accepted Answer

To identify the group of an element based on ionization enthalpies, observe the jump between successive values:
1.  **Element X:** The first ionization enthalpy ($IE_1$) is low (419 kJ mol⁻¹), but the second ionization enthalpy ($IE_2$) is extremely high (3069 kJ mol⁻¹). This huge jump indicates that removing the second electron disrupts a stable noble gas core. This is characteristic of **Alkali Metals** (Group 1), which have one valence electron ($ns^1$). (Note: The value 419 kJ mol⁻¹ corresponds to Potassium).
2.  **Element Y:** The $IE_1$ (590 kJ mol⁻¹) is higher than that of X, and the $IE_2$ (1145 kJ mol⁻¹) is roughly double the first. There is no sudden massive jump comparable to X, implying the second electron is also removed from the valence shell. This behavior is characteristic of **Alkaline Earth Metals** (Group 2), which have two valence electrons ($ns^2$). (Note: The value 590 kJ mol⁻¹ corresponds to Calcium).

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