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  • How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium?

3.17   How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium?

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The electronic configuration of Na and Mg are:

Na = 1s^22s^22p^63s^1   and  Mg = 1s^22s^22p^63s^2

So, the first electron in case of both has to be removed from 3s-orbital, but the nuclear charge of Sodium has +11 charge and Magnesium has +12 charge, which causes electrons to held more tightly in case of Mg, therefore, the first ionization energy of sodium is lower than that of magnesium.

After the first ionization happens, the second electron has to be removed from the p-orbital in case of sodium which has already attained its stable noble gas configuration and from the s-orbital in case of magnesium.

Therefore, 2nd ionization enthalpy of sodium is higher than that of magnesium.

Posted by

Divya Prakash Singh

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