[Donaldson Tan]

Define the term shell & subshell with regards to electronic configuration.Suggest the reason why Argon should behave as an inert gas despite the fact that it doesnt have a filled outer shell

[jdurg]

A shell is like the floor of an apartment building while the subshell is like little raised platforms on that floor.  All the subshells are part of the same shell, but they each have slightly different energy levels.  The 2s shell is like the flat ground of the second floor while the 1s shell is like the flat ground on the first floor.  

As for the second question, Argon IS a noble gas because it's outer shells ARE filled completely.    I think you might have said Argon when you meant Nitrogen.  

[Donaldson Tan]

Argon is in period 3. U would notice that the 3d subshell isn't filled at all.

[jdurg]

Ahhhh...  But that'd because the the 3d subshell is of a higher energy than the 4s and 4p shells.  Also, in order to have the 3d subshell filled, Argon would have to have ten more electrons added to it which would cause massive instability.  (Having a charge of +10 on an atom isn't too stable.  lol).  For the whole 3d thing having a higher energy, consider it a raised balcony which reaches up into the next floor.  The ladder leading up to the balcony is located on the third floor, which is why it's called 3d, but the level itself is actually up above some of the sublevels on the 4th floor.