Magnesium is found to have a higher first ionization energy value than aluminum, how would you explain this exception to the general trend in terms of electron arrangements and attraction/repulsion?

1 Answer
anor277
Nov 29, 2015

Consider the valence electron configuration of the 2 metal atoms. A priori , we would expect that a p -electron would be easier to remove than a s -electron.

Explanation:

For Mg, #Z# #=# #12#. Therefore its electronic configuration is #1s^(2)2s^(2)2p^(6)3s^(2)#; versus Al, #Z# #=# #13#; #1s^(2)2s^(2)2p^(6)3s^(2)3p^(1)#. While aluminum metal has extra nuclear charge, #p# orbitals demonstrably have zero electron density at the nucleus, and should be easier to ionize than the #s# electrons of the alkaline earth (why?), given that #s# orbital electrons have some electron density at the nucleus.

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