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  4. The first ionisation enthalpy of Na, Mg and Si are 496, 737, 776 kJ/mol respectively. What will be the first ionisation enthalpy potential of AI in kJ/mol?

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Q. The first ionisation enthalpy of Na, Mg and Si are 496, 737, 776 kJ/mol respectively. What will be the first ionisation enthalpy potential of AI in kJ/mol?

AIIMSAIIMS 2013Classification of Elements and Periodicity in Properties

Solution:

$Na , Mg , Al$ and $Si$ are in period $3 and as$ we move across the period, the atomic size decreases and hence ionisation enthalpy increases. So, the order is $Na < Mg < Al < Si$ Hence, IE of Al is greater than that of Mg $(737\, kJ\, / mol )$ and lower than that of Si $(776\, kJ\, / mol )$