2. INTERMOLECULAR FORCES OF ATTRACTION - A- A- A- Attraction existing between molecules in a given substance - R- R- R- Responsible for the phase of the substance at a given temperature; for example, strong IMFA – solid at room temperature; weak IMFA – gas at room temperature

3. COMPARISON OF MOLECULAR MASS, BOILING POINT SUBSTANCE MOLECULAR WEIGHT (amu) BOILING POINT (K) PROPANE CH 3 CH 2 CH 3 44231 DIMETHYL ETHER CH 3 OCH 3 46248 METHYL CHLORIDE CH 3 Cl 50249 ACETALDEHYDE CH 3 CHO 44294 ACETONITRILE CH 3 CN 41355

4. TYPES OF IMFA (weakest to strongest) 1. VAN DER WAAL’S FORCES a. London dispersion force – caused by the movement of the electrons around the nucleus - effect is very temporary - present in all substances and only force present in non-polar molecules

5. LONDON DISPERSION FORCE

6. Induced dipole – temporary charges due to presence of electrons from neighboring atoms

7. BOILING POINTS OF HALOGENS substance Boiling point ( o C) F2F2F2F2-188 Cl 2 -35 Br 2 60 I2I2I2I2185 The higher the number of electrons, the stronger is the London dispersion force.

8. SHAPE OF THE MOLECULE AFFECTS BOILING POINT

9. b. dipole-dipole interaction – present only in polar covalent molecules - caused by the dipole moment (differences in the electronegativy of the elements present)

11. Ethanol is Polar

12. F O N c. Hydrogen bonding - present in polar covalent compounds where hydrogen is directly attached to Fluorine, Oxygen and Nitrogen ( the three most electronegative elements)

13. Hydrogen bonding only occurs if H is attached to F, O and N.

14. Hydrogen bonding in water

15. H bonding in ice

16. 2. IONIC BONDING – -p-p-p-present only in ionic compounds. -E-E-E-Electrostatic force of attraction.

17. An ionic compound dissolved in water.

18. FORMULA TO DETERMINE THE NUMBER OF RINGS AND/OR DOUBLE AND TRIPLE BONDS 2 + 2C + N – H – X 2 ρ = where C = number of carbon atoms N = number of nitrogen atoms H = number of hydrogen atoms X = number of halogen (Group 17) atoms