As you have probably noticed, there are many more than the
basic 6 shapes in the database. The first step to teaching those shapes is to
explain the concept of “expanded valence.” First you teach the octet rule, and
then you tell them when its ok to break it, and what molecules look like when
you do.
Suggested activity #1
Have the students
look at some molecules in the database that exhibit expanded valence. The
“expanded valence” database automatically allows you to search these molecules,
but does not include the very complex shapes that are included in the “full
database.” We suggest that you choose some molecules from the list of shapes
and use them as an introduction to the concept of expanded valence.
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octahedral |
square planar |
trigonal bipyramidal |
t-shaped |
see-saw |
You can have the students
make note of which atoms often have more than 8 electrons around them, and then
tell them the general rule for determining if an atom is allowed to exhibit
expanded valence. (Row 3 and lower on the periodic table.)
Suggested activity #2
Students can make paper models of the “expanded valence”
shapes. It is often easier to connect the name with the shape if the student
can hold it in his/her hand and see how the “see-saw” shape can pivot like a
see-saw on their desk.
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