1. INTERMOLECULAR FORCES A quick foray into Chapter 12….

2. What does “INTER-” mean? InterstateInternetInteractIntercede Inter- means BETWEEN

3. What does “INTRA-” mean? IntrastateIntranetIntramuralIntravenous Intra- means WITHIN

4. WHAT ARE INTRAMOLECULAR FORCES? Ionic Bonds Metallic bonds Nonpolar covalent bonds Polar Covalent bonds Covalent network bonds The attractions that exist within the molecule

5. WHAT ARE INTERMOLECULAR FORCES? The attraction that exists between the molecules Since we are talking about “molecules” we are talking about COVALENTLY bonded atoms Also called Van der Waals Forces

6. Thought to ponder… How do we liquefy a gas? Or solidfy a liquid? (Think of 2 answers!) 1. Decrease the temperature Decreasing the temperature lowers the kinetic energy of the molecules. As a result, the molecules move more slowly. 2. Increase the pressure Increasing the pressure forces the molecules to move close together.

7. INTERMOLECULAR FORCES When we decrease the temperature and/or increase the pressure, the molecules have more contact with one another. As a result, they begin to interact. It is these interactions that cause a gas to condense into a liquid or a liquid to freeze into a solid.

8. INTERMOLECULAR FORCES The attractive forces between molecules are called INTERMOLECULAR FORCES (also known as IMFs). Please note that these forces are entirely different from chemical bonds. Please note that these forces are entirely different from chemical bonds.

9. INTERMOLECULAR FORCES The BLUE lines represent covalent bonds. The RED line represent IMF’s!

10. Temperature = Avg KE of Particles….. If that is true, then WHY can different phases of matter exist at the same temperature? Different molecules are attracted to each other differently (much like electronegativity of atoms…)

11. Strength of IMF’s ~ state of matter Gases have weak IMF’s so KE >> IMF Liquids have moderately strong IMF’s so KE~ IMF Solids have very strong IMF’s so KE << IMF KE << IMF

12. The state of a substance at a certain temperature is a good way to determine the strength of its IMFs Let’s compare Nitrogen, Carbon Dioxide, and Water: Clearly, from this you can tell that water has the strongest intermolecular forces while nitrogen has the weakest. Compound105 o C25 o C-5 0 C-80 o C-100 o C WaterGasLiquidSolid Carbon dioxide Gas Solid NitrogenGas Liquid

13. IMF For pure substances, there are 3 major types of intermolecular forces. In order to determine which forces are present, we must look at the shape and polarity of the molecules.

14. TYPES OF IMF 1.DIPOLE-DIPOLE FORCES Separation of charge in a polar molecule is called a dipole moment.Separation of charge in a polar molecule is called a dipole moment. Intermolecular forces between polar molecules are called dipole-dipole forces.Intermolecular forces between polar molecules are called dipole-dipole forces. This attraction comes from the fact that opposite charges attract each other.This attraction comes from the fact that opposite charges attract each other.

15. LONDON DISPERSION FORCES Also called induced dipole forces. When 2 nonpolar molecules bump into each other, the electrons in molecule repel the electrons in the other molecule. This results in a temporary dipole that lasts a fraction of a second. When this happens, each molecule causes the molecule next to it to become an instantaneous dipole- like a domnio effect.

16. LONDON DISPERSION FORCES

17. HYDROGREN BONDING Hydrogen “bonding” is a special type of dipole-dipole force. It occurs in molecules when hydrogen is bonded to N, O, or F, the three most electronegative elements. It describes the attraction 1 molecules H atoms for another molecules N,O, or F atoms. It is not actually a BOND.

18. HYDROGREN BONDING

19. RELATIVE STRENGTHS OF IMFS 1.When given a choice between hydrogen bonding and any other IMF, the hydrogen bonding ALWAYS wins. There is no exception to this rule. 2.In general, when comparing a polar molecule to a non-polar molecule (with similar molar masses), the polar molecule will have stronger forces.

20. RELATIVE STRENGTHS OF IMFS 3. When comparing two polar molecules,you must first decide if either one of the molecules undergoes hydrogen bonding. If one of them does, that molecule has the stronger IMFs. If neither molecule undergoes hydrogen bonding, you need electronegativity values to determine which has stronger forces. 4. When comparing two non-polar molecules, you need to look at the molar mass of each molecule. In this case, the heavier molecule will have stronger IMFs. (Heavier molecules have more electrons; this makes it easier to induce a dipole).

21. So…… For solubility, in general, like dissolves like. Polar sunstance will dissolve other polar or ionic substances Nonpolar substances will dissolve other nonpolar substances Molecules with HIGH IMF’s will have Strong attractions for each other High boiling points High melting points

22. Summary of Types of Intermolecular Forces Molecules are interacting Polar Molecules are interacting Hydrogen bonding if N,O or F is present Dipole-Dipole Interactions if no N, O or F Non-polar molecules are interacting London Dispersion Forces

23. Examples CH 4 H 2 S NH 3 London Dispersion Forces Dipole-Dipole Interactions Hydrogen Bonding