Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. – In a polar molecule, one end of the molecule is slightly negative, and the other end is slightly positive. Describing Polar Covalent Molecules: – A molecule that has two poles is called a dipolar molecule, or dipole. Example: δ+ δ– H— Cl δ+δ+δ-δ-

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A carbon dioxide molecule has two polar bonds, it is linear. O C O Therefore, the molecule is nonpolar. The effect of polar bonds on the polarity of an entire molecule depends on the shape of the molecule and the orientation of the polar bonds.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The water molecule also has two polar bonds. However, the water molecule is bent rather than linear. Therefore, the bond polarities do not cancel and a water molecule is polar.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Intermolecular attractions are weaker than either ionic or covalent bonds. Molecules can be attracted to each other by a variety of different forces: Intermolecular attractions: 1)The weakest attractions between molecules are called Van der Waals forces (London dispersion forces). Can be found between nonpolar molecules as O 2 (g), H 2 (g), Cl 2 (g), CO 2 (g).

2) Dipole interactions occur when polar molecules are attracted to one another. Ex. HCl(g), HBr(g). These interactions are stronger than Van der Waals, but much weaker than ionic bonds. + ++= _ + _

3) Hydrogen Bonds: Are attractive forces in which a hydrogen covalently bonded to a very electronegative atom (F, O, N) is also weakly bonded to an unshared electron pair of another electronegative atom. Hydrogen bonding always involves hydrogen. O δ- O δ- H δ+ H δ+ O δ- H δ+ H δ+

Hydrogen bonds are the strongest of the intermolecular forces. They are extremely important in determining the properties of water and biological molecules. Ex: Water is liquid at room temperature because the hydrogen bond between its molecules. Boiling Points: H 2 O 100 o C H 2 S - 60 o C H 2 Se o C

Intermolecular attraction forces (weaker than ionic & covalent bonds) Van der Waals (the weakest) Nonpolar molecules Dipole-dipole (stronger than ) Polar molecules Hydrogen bonds (the strongest) Molecules containing F-H; O-H or N-H