1. Intermolecular Forces

2. Intermolecular vs Intramolecular Intramolecular forces are forces within a molecule such as covalent bonds

3. Intermolecular vs Intramolecular Intramolecular forces are forces within a molecule such as covalent bonds Intermolecular forces are forces between molecules

4. Intermolecular vs Intramolecular Intramolecular forces are forces within a molecule such as covalent bonds Intermolecular forces are forces between molecules From: http://webclass.lakeland.cc.il.us/iali/CHM151Folder/BLB-Chapter11.htm

5. Intermolecular Forces We will consider three types of intermolecular forces Dipole-dipole bonding Hydrogen bonding Van der Waals forces

6. Dipole-dipole bonding This occurs between polar molecules The positive end of one polar molecule is attracted to the negative end of another From: http://commons.wikimedia.org/wiki/Image:Dipole-dipole-interaction-in-HCl-2D.png

7. Dipole-dipole bonding in general From: http://stezlab1.unl.edu/reu1999/dputn226/ChemHelp/RET_Web_Pages/im_forces/Intmole_Forces.htm

8. Hydrogen Bonding This is a special case of dipole-dipole bonding

9. Hydrogen Bonding This is a special case of dipole-dipole bonding It occurs when hydrogen is bonded to nitrogen, oxygen or fluorine

10. Hydrogen Bonding This is a special case of dipole-dipole bonding It occurs when hydrogen is bonded to nitrogen, oxygen or fluorine These are the strongest cases of dipole- dipole bonding because of the high electronegativity of F, N and O

11. Hydrogen Bonding This is a special case of dipole-dipole bonding It occurs when hydrogen is bonded to nitrogen, oxygen or fluorine These are the strongest cases of dipole- dipole bonding because of the large difference in electronegativity Very important in the properties of water

12. Hydrogen Bonding Hydrogen bonding movie From: www.ualr.edu/botany/botimages.html

13. Van der Waal’s forces These are the weakest intermolecular force

14. Van der Waal’s forces These are the weakest intermolecular force They occur between all molecules but are ignored when either dipole-dipole or hydrogen bonding is present as they are much stronger

15. Van der Waal’s forces These are the weakest intermolecular force They occur between all molecules but are ignored when either dipole-dipole or hydrogen bonding is present as they are much stronger These are due to temporary instantaneous dipoles formed in atoms and molecules as the electrons move around the nucleus/nuclei

16. Van der Waal’s forces These are also sometimes called dispersion forces or London dispersion forces or London forces Van der Waal’s forces increase with increasing mass From: www.chem.purdue.edu/gc help/liquids/disperse.html

17. Van der Waal’s animation Animation

18. Intermolecular Forces strength Strongest:Hydrogen Bonding.Dipole-dipole bonding Weakest:van der Waal’s forces

19. Boiling temperatures The presence of hydrogen bonding explains why water, hydrogen fluoride and ammonia have a higher boiling point than the other hydrides down the same groups, even though their mass is less E.g. water compared to hydrogen sulfide

20. Boiling Temperatures From: www.cem.msu.edu/~reusch/VirtualText/physprop.htm

21. Question What type of bonding would occur between the following molecules? N 2 HF CO 2 H 2 S CH 4 NH 3

22. Question - Answers What type of bonding would occur between the following molecules N 2 -Van der Waals as a non-polar molecule HF - hydrogen bonding as polar with H bonded to F, N or O CO 2 - Van der Waals H 2 S - dipole-dipole bonding as a polar molecule CH 4 - Van der Waals as a non-polar molecule NH 3 - hydrogen bonding