Chemical Bondingand Molecular Structure

Chapter 12Sec 12.8 - 12.10

Goals:

1. To use Lewis Structures as a way to predict the geometry of Molecules

2. Determine if molecules are polar or nonpolar

VSEPR Model

• Valence Shell Electron Pair Repulsion Model

• Bonds (pairs of electrons) attempt to move as far away as possible from one another in a molecule

This explains the Geometry of H2O

Water is a “bent” molecule, because

of the lone pairs around the central

Oxygen atom

Various Geometry of Molecules

See Examples on Next Slides

(Hand-Out)

Polar or Non-polar Molecule?

A molecule may have polar covalent

bonds and not be polar overall

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Geometry must also be considered

Ammonia (NH3) is polar

1. The bonds between hydrogen and nitrogen are polar covalent (∆EN = .87)

2. Pyramidal geometry of molecule points charges toward N

Carbon Dioxide is Non-polar

Even though the bonds between carbon and oxygen are polar covalent (∆EN = 1.0), the pull of electrons is in equal and opposite directions because CO2 is linear

Water is Wacky!

Water has some strange properties due to its structure