[vhpk]

Hi all,
I've got some unclear problems and want to ask your for clarification:
1/ Why is the filled subshell more stable than partially filled subshell ? Is there any different reason rather than the stable configuration of noble gas or pseudo-noble gas. If so, why is the IE of the noble gas high abnormally ? why is the IE of the transition metal almost the same and get the unusually highest in the metal of group XB ?
2/ Why is the partially filled subshell stable ? Is the reason that, all the electrons are arranged singly and has the same spin, so they're far from each other and the repulsive force is reduced --> stable ?
Thanks a lot. )

[renge ishyo]

The ultimate reason for any of this eludes us if you really must know, but I'll at least attempt to say a few things that might help you think about things at least. Loosely speaking, in chemistry stable species don't tend to react whereas unstable species react to form chemical bonds. So the first question can be phrased, under what circumstances do species form chemical bonds with one another?

When two electrons are present in an orbital the electrons tend to cancel out the magnetic moments of each other resulting in a stable arrangement known as diamagnetism. If all the orbitals are filled in the atom there is no net magnetic moment for the atom as a whole. With no net magnetic moment, this atom will not move towards a nearby magnet. Argon is an example of an atom of this type, and it does not tend to form chemical bonds. In contrast, a lone electron that is unpaired in an orbital (say for the Hydrogen atom) is paramagnetic...it's magnetism is not cancelled out in the orbital that it resides in, and it will move towards another magnet if one should come near. This "other magnet" can be another unpaired electron in a separate atom (say another H atom), and, symmetry permitting, the two orbitals on the two different atoms can overlap and share the two electrons together. This "chemical bond" that forms between the two is somewhat diamagnetic in nature now because the electrons in the molecular bond can now help cancel each other's magnetism. Thus, the new molecule that forms (H₂) is less reactive than the two individual atoms by themselves with unpaired electrons. If the atom already has achieved a diamagnetic configuration (like Argon, or any of the noble gases for that matter) it will have little incentive to react with a nearby atom or molecule to form a bond since the net magnetism of the atom is already so low. An Argon atom tends to just stay by itself.

The second question is a different sort and has more to do with the stability of the arrangement inside an atom as opposed to how that atom interacts with the outside world (which was discussed above). The stability that they refer to in this case has more to do with how easily an one electron in nitrogen can move around to a different orbital (say, the lowest unoccupied orbital) within the atom compared to how easily you can move an electron in say carbon from one p orbital to an "empty" one.  The reason has to do with symmetry, the more symmetrical the arrangement the harder it is to break the symmetry. For instance, Nitrogen has a half filled orbital that imparts with it a certain stability that makes its electrons harder to move around than nearby atoms such as carbon with orbitals that have unfilled and therefore unsymmetrical arrangements. However, keep in mind that a lone nitrogen atom, despite its half filled orbitals, will react explosively with another nitrogen atom in order to fill those orbitals and cancel out the net magnetism. The "stability" that chemists talk about is always a relative thing unfortunately.