• # question_answer 6) The first ionisation enthalpy (${{\Delta }_{i}}H$) values of third period elements, Na, Mg and Si are respectively 496, 737 and $786KJ\,mo{{l}^{-1}}$. Predict whether the first (${{\Delta }_{i}}H$) value for $Al$ will be more close to 575 or $760KJmo{{l}^{-1}}$ ? Justify your answer.

It will be more close to $575\,KJmo{{l}^{-1}}$. The value will be less than that of Mg because the electron has to be removed from $3p$-orbital which is singly occupied. In Mg, the electron is removed from filled $3s$-orbital which requires more energy.

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