The document discusses how electrons arrange themselves around an atomic nucleus based on the principle that systems tend toward lower potential energy states. It explains that electrons experience repulsion from other electrons but attraction to the positively charged nucleus. Through experiments arranging different numbers of electron pairs around a nucleus, the document aims to determine the angles that electron pairs form to minimize potential energy and predict molecular geometry.

1. Discovering Molecular Shapes
An Introduction to Valence Shell Electron
Repulsion Techniques

2. Systems Tend toward Low Energy
States
This high potential energy
state is “unstable.”
What will happen if the triangular
block is removed?

3. Systems Tend toward Low Energy
States
See what happens if the
triangular block is removed?

4. Systems Tend toward Low Energy
States
High potential energy
state
Low potential energy
state
Unstable high energy
state tends to change to
low energy, and give off
light, heat or other energy

5. Now oppositely charged particles
attract
Attractive Force
Separate, these charges are at high potential
energy
They will reduce energy by coming together

6. Identically charged particles repel
Repulsive Force
Together, these charges are at high potential
energy
They will reduce energy by separating

7. Identically charged particles repel
Repulsive Force
They will reduce energy by separating

8. Identically charged particles repel
They will reduce energy by separating

9. Now we can discuss how
electron pairs arrange
themselves around the nucleus
What do you think
controls their position?
They will take the positions
that produce the lowest
potential energy

10. Remember, the electrons in
their orbitals are attracted to the
nucleus.
That means they can
swing around the nucleus
like spokes on a pivot

11. Remember, the electrons in
their orbitals are attracted to the
nucleus.
Electrons attracted to the nucleus may move
around the nucleus, but will always stay
close to it

12. Let's look at how two electron pairs
would swing around the nucleus
If we position them at 90º
angles, they swing away
from each other

13. Let's look at how two electron pairs
would swing around the nucleus
Does it make
sense that
they would
get as far
away from
each other as
possible?

14. Two electron centers would be at
lowest energy at a 180 degree angle
So they
would
vibrate
about an
angle of
180º

15. Let's experiment with two, three and
four electron pairs
The purpose of the
investigation is to find out
what angles to expect the
electron pairs to make
with each other.

16. Let's experiment with two, three and
four electron pairs
Then we can attach
atoms to the orbitals at
those angles and see
what the molecular
geometry will be.