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VSEPR

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VSEPR

Valence Shell Electron Pair Repulsion Theory

www.longview.k12.wa.us/ralong/tietjen/Chemistry/VSEPR.JAT.ppt

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

Vocabulary:

“lone pair” = “non-bonding pair” = “unshared pair”

= any electron pair that is not involved in bonding

“domain”

= any electron pair, or any double or triple bond is considered one domain.

“bonding pair” = “shared pair”

= any electron pair that is involved in bonding

LINEAR

- 2 domains
- both are bonding pairs
- They push each other to opposite sides of center (180 apart).

BeCl2

TRIGONAL PLANAR

- 3 domains
- all are bonding pairs
- They push each other apart equally at 120 degrees.

GaF3

TETRAHEDRAL

- 4 domains
- Each repels the other equally - 109.5 - not the expected 90.
- Think in 3D.

CH4

- 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.

- Shared (bonding) pairs are “stretched” between two atoms that want them.
- “Longer & Thinner”

- Unshared (non-bonding) pairs are not “stretched.”
- “Shorter & Thicker”

- 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).