Chapter 8 Prediction of Molecular Geometry VSEPR Molecular

Chapter 8: Prediction of Molecular Geometry (VSEPR)

Molecular Shapes: The VSEPR Model VSEPR: Valence-Shell Electron-Pair Repulsion model - Electrons in bonds and in lone pairs can be thought of as “charge clouds” that repel one another and stay as far apart as possible, this causing molecules to assume specific shapes.

Linear molecules: Two Charge Clouds The CO 2 molecule Geometry- linear - Central atom (C) binds to two other atoms The HCN molecule Geometry- linear - Central atom (C) binds to two other atoms

Planar molecules: Three Charge Clouds The H 2 CO molecule Geometry- Trigonal Planar - Central atom (C) binds to three other atoms The SO 2 molecule Geometry- Bent - Central atom (S) binds to two other atoms with one lone pair

Tetrahedral Molecules: Four Charge Clouds

Tetrahedral Molecules: Four Charge Clouds

Bipyrimidal molecules: Five Charge Clouds

Trigonal Bipyrimidal structure Structure of PCl 5 forms a trigonal bipyrimidal shape

Electron pairs within this shape generally occupy the equatorial positions

Electron-Dot Structures of Polyatomic Molecules Draw an electron-dot structure for SF 4. Step 1: 6 + 4(7) = 34 valence electrons F F Step 3: S F F F S Step 2: F F F Step 4: S F F

The geometry of sulfur tetraflouride (SF 4) is a seesaw

Look at the geometry of CLI 3

The geometry of I 3

Octahedral molecules: Six Charge Clouds

Electron pairs first occupy the axial positions before the equatorial positions

Electronegativity and the periodic table