Models Models are attempts to explain how nature operates on the microscopic level based on experiences in the macroscopic world. Models can be physical as with this DNA model Models can be mathematical Models can be theoretical or philosophical

Fundamental Properties of Models A model does not equal reality. Models are oversimplifications, and are therefore often wrong. Models become more complicated as they age. We must understand the underlying assumptions in a model so that we don’t misuse it.

VSEPR Model The structure around a given atom is determined principally by minimizing electron pair repulsions. Bonding electron pairs and nonbonding electron pairs spread as far apart as possible to minimize electrostatic repulsion. (Valence Shell Electron Pair Repulsion)

Predicting a VSEPR Structure Draw Lewis structure. Convert Lewis structure to VSEPR notation. Convert Lewis structure to VSEPR notation. Determine parent shape of the molecule. Determine parent shape of the molecule. Determine the molecular shape of the molecule. Determine the molecular shape of the molecule.

Writing VSEPR Notation VSEPR notation follows the general form AX m E n A = the central atom A = the central atom X = outside atoms (bonding pairs of e - ) X = outside atoms (bonding pairs of e - ) E = nonbonding pairs of e - on central atom E = nonbonding pairs of e - on central atom m & n = numbers of bonding & nonbonding pairs respectively m & n = numbers of bonding & nonbonding pairs respectively

Table – VSEPR Structures

VSEPR and the water molecule

VSEPR and the ammonia molecule

VSEPR and a molecule of I 3 Which structure is the correct one?

VSEPR and Xenon tetrafluoride Which one will it be???

VSEPR and Phosphorus hexachloride