Ask A Scientist Chemistry Archive

name         David W.
status       educator
age          40s
	
Question -   Hello,
I am an 8th grade science teacher and a life science person primarily.

I am currently teaching atomic structure and am having a hard time
explaining suborbitals and their configuration to my students.

They understand energy levels but if you have a good explanation of the
configurations for the s p d and f suborbitals I would appreciate it. .
.  or know of a good web site to point me to.
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This is not an easy question to answer at the 8th grade level, but here is
a shot at it.
    First, you (the students, teachers, and experts) have to abandon our
intuition about "how" electron behave. Early on we are told they are like
the "planets" orbiting around the Sun, but that analogy later causes
confusion because it is not a very accurate analogy. In atoms and molecules,
electrons behave more like waves, and this analogy is only approximate but
let us go with it for now. It is a wave moving in not 1, but in 3 dimensions.
You can demonstrate waves in 1 dimension with a string, 2 dimensions with a
drum, but 3 dimensions is more difficult to see. A large soap bubble is the
best approximate analogy. A large bubble does not stay just spherical, but it
deforms in many ways some more "egg-like" others more "cigar-like". They
have different shapes. The same is true of electrons. Their waves have
different "shapes" too. Some of these shapes are "unstable" and "appear" /
"disappear" very quickly. However, there are some shapes that are "stable"
and are able to keep their shapes. You can show an analogy by plucking a
stretched rubber band. If you look closely you can see the fundamental and a
few of the shorter wavelength overtones. The shorter wavelengths have higher
energy, that is higher frequency waves. A similar thing is true for
electrons in atoms and molecules.
    Second, now onto electrons. There are some electron shapes that are
spherically symmetric. The lowest energy one "looks" like an electronic
sphere, but higher energy electrons "look" like spheres inside of spheres.
These are called 's' orbitals for historical reasons. You have to name them
something and s-orbitals is their name. The 1s orbital looks like a sphere,
the 2s orbital looks like a sphere within a sphere, the 3s orbital looks
like a sphere within a sphere within a sphere and so on... But that is not
the only way electrons can move within an atom or molecule.
    The electron waves can move in 3 dimensions in patterns that look like 3
"pinched" cigars -- one pointing in each of the 3 space dimensions x, y, and
z. These are called 'p' orbitals for historical reasons. Again you have to
call them something and they are called 'p' orbitals. The lowest stable 'p'
orbital has a single pinch and it is designated '2p' because it is partners
with the '2s' orbital. A '1p' orbital is not stable and if it appears, it
quickly disappears. The higher energy 'p' orbitals (3p, 4p, etc.) have 2
pinches, 3 pinches in them and so on.
    The next stable way electrons move in atoms and molecules look more
complicated and do not try to get into any more detail because it will only
cause confusion, but their names are 'd' orbitals for historical reasons.
There are 3d, 4d, etc. partnered up with the (3s,3p) and (4s,4p) orbitals.
    It turns out that each individual stable orbital can hold exactly 2
electrons. If three electrons "try" to get into the same orbital at the same
time -- for example: 2s3, where the '3' stands for 3 electrons, this is very
unstable and that motion of the electrons quickly disappears.
    You can then start with the "rules" for filling orbitals, but emphasize
to the students that these are THE RULES they describe the stable motions of
electrons so they are not subject to debate or discussion. The WHY of the
rules requires a lot deeper digging into the mechanics of electrons.
Hope this helps a bit.

Vince Calder
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