CHEM 1070 1st Edition Lecture 22 Outline of Last Lecture II. Covalent and Ionic BondsOutline of Current Lecture III. Intermolecular ForcesIV. Dispersion ForcesV. Permanent DipolesVI. Hydrogen BondsVII. Properties of LiquidsVIII. Phase, intermolecular interavtionsCurrent LectureIntermolecular ForcesIntermolecular Forces: Attractions between “particles” that hold them together. These forces depend on the distribution of electronic charge and often depend on the shape of the molecule and the atoms that form it. Important ideas: • Like charges repel• Unlike charges attract• The closer the charges the stronger the interaction • The higher the charge the stronger the interaction -States of Matter & intermolecular forces• Solid ‐ strong intermolecular interactions dominate behavior – Solid matrix rigid; dense– Molecules very close and interacting • only vibrational motion – Volume fixed • Liquid – strong intermolecular interactions less than solid but still dominate properties – Liquid matrix conform to vessel shape; dense– Molecules close and interacting but not rigidly held • some motion – Volume fixed • Gas ‐ little or no intermolecular interactions – Gas matrix fill vessel; not dense– Molecules very distant and not interacting • moving quickly– Volume strongly affected by P and T; fill vessel Dispersion Forces• Also known as London forces or instantaneous dipoles. • Caused by distortions in the electron cloud of one molecule inducing distortion in the electron cloud on another. • Distortions in the electron cloud lead to a temporary dipole. • The temporary dipoles lead to attractions between molecules— dispersion forces. • All molecules have attractions caused by dispersion forces. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Permanent DipolesPermanent dipoles occur when electro negative atoms are bonded in a asymmetric arrangements. ‐– Polar molecules – Molecular dipole (debyes, D) H Bonds vs. Chemical Bonds ‐• Hydrogen bonds are not chemical bonds.• Hydrogen bonds are attractive forces between molecules. • Chemical bonds are attractive forces that make molecules through shared electrons of atoms. Properties of Liquids• Liquids tend to minimize their surface—a physical phenomenon, surface tension. • This tendency causes liquids to have a surface that resists penetration. • The stronger the attractive force between the molecules, the larger the surface tension • Molecules in the interior of a liquid experience attractions to surrounding molecules in all directions. • Molecules on the surface experience an imbalance in attractions, effectively pulling them in. • To minimize this imbalance and maximize attraction, liquids try to minimize the number of molecules on the exposed surface by minimizing their surface area. • Stronger attractive forces between the molecules = larger surface tension. Phase, Intermolecular Interactions Temperature (K)  average kinetic energy – Molecular motion  Temperature (K)– Thermal energy – drives molecular motion • Intermolecular Forces vs Thermal Energy Thermal Energy >> Intermolecular Forces → Gas Thermal Energy < Intermolecular Forces Increased thermal energyovercome intermolecular forces, tend to drive molecules from condensed to gas