1. 1 Ionic Forces + + - - - - + ++ Ion-Ion e.g. NaCl(s) Ion-Dipole e.g. NaCl(aq) The positive ions form strong intermolecular forces with the positive side of the polar molecule of water. Ion-ion forces are very strong and produce high boiling points and melting points. NaCl dissolved in water What is wrong?

2. 2 London Dispersion Forces The electrons on one atom are moving randomly and this creates a temporary dipole on the first atom. The instantaneous dipole on the first atom then induces an instantaneous dipole on the second atom. The two induced dipoles attract each other. London Dispersion Forces are proportional to a molecule’s polarizability, which is the ease with which the electron cloud can be deformed. The polarizability, is approximately proportional to the electronegativity of the molecule. What is wrong? Fritz London 1900-1954.

3. 3 Dispersion forces also depend upon the molecular shape. C 5 H 12 n-pentane T bp = 9 o C Dimethylpropane T bp = 36 o C Large Contact Area (Surface Area) Small Contact Area (Surface Area) What is wrong?

4. 4 Propane CH 3 CH 2 CH 3 Acetonitrile CH 3 CN 44 electrons T bp = -42 o C 41 electrons T bp = +82 o C No Dipole Moment Large Dipole Moment Why is the boiling point of acetonitrile so much higher than the boiling point of propane??? London Forces What is wrong?

5. 5 Hydrogen Bond ++ -- ++ -- What is wrong?

6. 6 Vapor Pressure Rises with Temperature Temperature Vapor Pressure At higher temperatures, less molecules have sufficient energy to escape from the liquid. What is wrong?

7. 7 Temperature ( o C) Pressure (atm) SolidLiquidVapor P2P2 vaporization 4.6 torr 0.01 What is wrong?

8. 8 Phase Diagram of water Phase Diagram of water Temperature ( o C) Pressure (atm) P1P1 SolidLiquidVapor P2P2 Melting + Vaporization Sublimation 5.1 -56 What is wrong?

9. 9 Phase Transitions Solid Gas Liquid Melting Freezing Condensation Enthalpy Sublimation Deposition vaporization What is wrong?

10. 10 Heating Curves Heat Added (Joules) Temperature ( o C) T mp T bp 1. Heating solid 1 2. Melting solid to liquid 2 3. Heating gas 3 4. Vaporizing liquid to gas 4 5. Heating liquid 5 What is wrong?

11. 11 Covalent-Network Solids Form of particles: Atoms connected in network of covalent bonds Properties: Very soft Very high melting point Examples: Diamond (C), Quartz (SiO 2 ) Diamond Each carbon is connected to 4 others by a covalent bond What is wrong?

12. 12 Ionic Solids Form of particles: Positive and negative ions Forces between particles: Electrostatic attractions Properties: Hard and Brittle High melting point Poor electrical conductivity when molten Examples: All typical salts. e.g. NaCl, Ca(NO 3 ) 3, MgBr 2 + + - - - - + ++ What is wrong?

13. 13 Metallic Solids Properties: Soft to very hard Low to very high melting point Poor thermal and electrical conductivity Malleable and Ductile Examples: All metals. e.g. Cu, Fe, Sn, Au, Ag Bonding due to delocalized valence electrons (shown in blue) What is wrong?

14. 14 Molecular Solids Forces between particles: Dispersion Dipole-Dipole (if molecules are polar) Hydrogen Bonds (if O-H, N-H, F-H) Properties: Fairly soft Moderately low melting point (usually <200 o C) Poor thermal and electrical conductivity Examples: SiO 2 What is wrong?