1. Electronegativity, Polar Bonds, and Polar Molecules Thursday February 23 rd, 2006 http://charlescurtis.ca

2. Polar Covalent Bond When the two atoms in a covalent bond are different, one atom will have a greater attraction towards the electrons. On average the electrons will spend more time around the atom with a greater electronegativity. This creates a polar bond. Slight build up of charge on an each atom in the covalent bond.

3. Electronegativity Measure of the attraction of the electrons towards an atom in a covalent bond. A higher value means a greater attraction.

5. Polar Bond One atom in the bond will become slightly positively charged while the other atom will become slightly negatively charged. The atom with the higher electronegativity will be slightly negatively charged (δ-) The atom with the lower electronegativity will be slightly positively charge (δ+)

6. Methanol

7. Using Electronegativity to Predict the type of bonding (Ionic vs Covalent)

8. Polar Molecules Covalently bonded molecules, (which contain bonds from two different atoms), which are not symmetrical will form POLAR MOLECULES The symmetry of symmetric molecules cancels out the effect of polar bonds. Polar Molecules will have a positive end and a negative end. CH 4 CCl 4 CO 2

9. Intermolecular Forces van der Waals Forces dipole-dipole forces London Dispersion Forces Hydrogen Bonding

10. Dipole-dipole Much weaker than ionic or covalent bonds

11. London Dispersion Forces There are always weak forces holding molecules together. Causes by temporary dipole-dipole interactions caused by fluctuations of electron cloud. Weaker than dipole-dipole forces

12. Hydrogen Bonding Water Molecule vs Chlorine Gas Compare Molecular Masses. Water = 18 g/mole Chlorine gas =70 g/mol All things being equal (but mass), which would boil easier?

13. Hydrogen Bonding

14. High or Low Intermolecular Forces Atmospheric Gases H 2 CH 4 N 2 O 2 Sugar NH 3

15. In Class Homework Assignment p84 #1-4 p88 #8-12 Due at the end of class When done homework, start reading section 2.5, which is on naming compounds.

16. Section 2.5 is the last section of Chapter 2. Quiz Friday on section 2.1 to 2.3 Test sometime mid next week. Article Assignment Due Next Tuesday. A lot of Article Assignment #1 not handed in.