The trend for ionization energy is a general increase from left to right across a period. However, magnesium (Mg) is found to have a higher first ionization energy value than aluminum (Al). Explain this exception to the general trend in terms of electron arrangements and attraction/repulsion.

Question

anonymous · Answer

it is due to stable electronic configuration of magnesium
Mg=1s2 2s2 2p6 3s2 here s orbital in the last sell is full filled hence has higher ionization energy 
Al= 1s2 2s2 2p6 3s2 3p1
it has one unpaired electron which can be easily removed !!!