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.

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.