1. 1 Fall, 2013 Instructor: J.-W. John Cheng Mech. Engr. Dept., Nat ’ l Chung Cheng Univ. Ch 2. Intermolecular Energies Interfacial Physics and Thin-Film Processing

2. 2 2.0 Chapter Overview

3. JCheng201309 3 How Things Come Together? Atom Molecule Cluster Phase * covalent bonding (electron sharing) non-covalent bonding intermolecular interaction (no electrons sharing) * phase: molecules aggregated in bulk thru non-covalent interactions

4. JCheng201309 4 Intermolecular Forces vs. Molecular Forces Molecular force binding atoms together changes and merges the electron charge distributions of individual atoms Intermolecular force binding atoms/molecules together only perturbs the electron charge distributions individual atoms/molecules remain as distinct entities One example is the van der Waals force

5. JCheng201309 5 Intermolecular Energies Involving Ions Charge (Q 1 )-charge (Q 2 ) interaction (ions) Ion (Q)-dipole (u) interaction Ion (Q)-induced dipole (  0 ) interaction w(r): potential energy  0 : polarizability of non-polar molecule

6. JCheng201309 6 Intermolecular Energies Involving Polar Molecules Dipole (u 1 )-dipole(u 2 ) interaction Dipole (u)-induced dipole interaction

7. JCheng201309 7 Intermolecular Force between Non- Polar Molecules instantaneous dipole moment In average, they appear to be 2 non- polar molecules time t contd

8. JCheng201309 8 Intermolecular Energy Involving Non- Polar Molecules Induced dipole-induced dipole interaction * h = the energy of an electron in the first Bohr radius = energy needed to ionize the atom – the 1st ionization potential

9. JCheng201309 9 A Special Intermolecular Interaction between Polar Molecules Hydrogen bonding Hydrogen is easy to lose its only electron when bonded to a strongly electronegative atoms, O, N, or F Becoming partially positively charged, H  + Then attracted to neighboring ions (e.g. Cl - ) or partially negatively charged atoms (e.g. O  - ) or molecules About 10 times stronger than direct dipole-dipole interaction * In this class, effect of hydrogen bonding is ignored

10. JCheng201309 10 Chapter Organization 2.1 Charge-charge interaction 2.2 Charge-dipole interaction 2.3 Charge-induced dipole interaction 2.4 Dipole-dipole interaction 2.5 Dipole-induced dipole interaction 2.6 Non-polar interaction 2.7 van der Waals interaction 2.8 Summary of intermolecular potentials 2.9 References 2.A Boltzmann distribution