Question
Question: The first ionisation enthalpies of Na, Mg, Al and Si are in the order :...
The first ionisation enthalpies of Na, Mg, Al and Si are in the order :
A
Na < Mg > Al < Si
B
Na > Mg > Al > Si
C
Na < Mg < Al < Si
D
Na > Mg > Al < Si
Answer
Na < Mg > Al < Si
Explanation
Solution
Across the period (i.e. 3rd period) the size of atom decreases and nuclear charge increases. So generally the ionisation energy increases. However the ionisation energy of Mg is greater than Al because of more penetration power of 2s sub-shell electrons of Mg as compared to that of the 2p sub-shell electron of Al. Also, Mg has fully filled configuration.