Question

Aluminium is stable in nature so why it has valency 3+

Answer 1

Answer:

Well this all goes down to basically what we call the orbital level. The atomic number for Aluminuim (Al) is Z=13.

The electronic confugration thus becoming:

Al (13) :

 1s² 2s² 2px² 2py² 2pz² 3s² and 3px¹ 3py∅ 3pz∅

Where ∅=0  

Thus for bonding one electron from the 3px¹ is readily available but since two electrons from the 3s² orbitals are also available because of the fact that this orbital has same value of "n" .They also get excited to a higher energy level and thus changing the electronic confugration to  

1s² 2s² 2px² 2py² 2pz² 3s∅ 3px¹ 3py¹ 3pz¹.

This way Aluminium achieves a much stable electronic confugration because of exactly half filled p-subshell (orbital). This way aluminium exhibits a valency of +3 instead of +5.