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Octet rule
Name: tom hammargren
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: 1999
Question:
I've heard that atoms or ions try to get eight electrons in
their valence shells and by doing so they become more stable
and unreactive. I don't hear about WHY, when the octet rule
is obeyed, atoms or ions are more stable and less reactive.
For example, is neon unreactive for reasons more than
simply the s and p subshells are filled with eight electrons?
Replies:
An excellent question, tom...basically, the octet rule
is a simple way of rationalizing why the first two
rows of the periodic table behave the way we do.
It is not a "law of nature," but rather a "rule of thumb"
which, when applied, does have some predictive power.
Another way to think of the octet rule is as an "organizing
principle," which means that it organizes a lot of data
into one simple idea by observing patterns in experimental
data such as atomic ionization energies, electron affinities,
etc. But there are many exceptions to the octet rule...
Fundamentally, since atoms are quantum-mechanical objects, one
needs to apply the "full force" of quantum theory to begin to
grasp the reasons why an octet is a relatively stable way to be.
These have to do with the special properties of electrons,
which as spin=1/2 particles, find it energetically advantageous
to be able to change places with other electrons once in awhile,
but only if they have the same "spin"...an amazing effect
known as fermion exchange. However, this is counterbalanced by
the fact that the electrons repel one another electrically...taking
both of these into account, one can rationalize most of the
periodic table (at least the first few rows).
To explain further, I'd have to ask you to sit in on the university
course I teach in general chemistry. Maybe you'll consider just taking
such a course yourself..?
- best wishes, topper
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