1. Valence Shell Electron Pair Repulsion Theory
VSEPR
Valence Shell Electron Pair Repulsion Theory

2. TEKS
7 (E) predict molecular structure for molecules with linear, trigonal planar, or tetrahedral electron pair geometries using Valence Shell Electron Pair Repulsion (VSEPR) theory.

3. Vocabulary:
“domain”
= any electron pair, or any double or triple bond is considered one domain.
“lone pair” = “non-bonding pair” = “unshared pair”
= any electron pair that is not involved in bonding
“bonding pair” = “shared pair”
= any electron pair that is involved in bonding

4. 2 domains on central atom
LINEAR
2 domains
both are bonding pairs
They push each other to opposite sides of center (180 apart).
BeCl2

5. 3 domains on central atom
TRIGONAL PLANAR
3 domains
all are bonding pairs
They push each other apart equally at 120 degrees.
GaF3

6. 4 domains on central atom
TETRAHEDRAL
4 domains
Each repels the other equally  - not the expected 90.
Think in 3D.
CH4

7. Steps for using VSEPR: Draw a Lewis Dot Structure.
Predict the geometry around the central atom.
Predict the molecular shape.
… also, we can try and predict the angles between atoms.

8. All e- pairs push each other as far apart as possible.
Shared (bonding) pairs are “stretched” between two atoms that want them.
“Longer & Thinner”
Unshared (non-bonding) pairs are not “stretched.”
“Shorter & Thicker”

9. Electron Pair Repulsion
2 lone pairs require the most space & repel each other the most, resulting in the greatest distance (angle).
1 lone pair (thick) & 1 bonding pair (thin) require less space
2 bonding pairs (both thin) require the least space & repel each other the smallest distance (angle).