Polarity of Molecules Objectives: 1. State the two factors that determine polarity of a molecule. 2. Explain how the structure of a molecule helps determine its properties. Key Terms: Dipole, hydrogen bond, dispersion forces

Determining Polarity – bond polarity Determining polarity requires looking at the type of bond as well as the shape of the molecule.type of bond – Bond polarity is determined by looking at the electronegativity differences between the atoms that are covalently bonded

Determining Polarity – single element Molecules consisting of a single element are all non-polar. (O 2, O 3, H 2, N 2, Diamond,...) – Chlorine (Cl 2 )

Determining Polarity – asymmetric electronegativities If the electronegativities are dissimilar on the opposite sides of a molecule chances are that the molecule is polarelectronegativities – HCl, NH 3, and CH 3 Cl are asymmetric polar – BF 3 and CCl 4 are symmetric Non-polar

Determining Polarity – axis of symmetry Molecules that form mirror images (symmetrical) of themselves are non-polar even though their bonds appear polar. (CO 2, CCl 4, BF 3, H 3 O +,…)

Determining Polarity – unshared electron pairs Molecules that contain unpaired electrons are usually polar. Look at water and ammonia.

Intermolecular Forces Vanderwahls Forces: – Dipole interactions attraction of the positive and negative sides of a polar atom – Dispersion forces (temporary dipole) temporary rearrangement of charge in non-polar atoms (weakest intermolecular force) Hydrogen bonding – dipole interaction between a hydrogen that is already covalently bonded to O, N, or F and another negative diplole or ion (strongest intermolecular force) – important for determining the properties of water