CH 102 1st EditionExam# 1 Study Guide Lectures: 1 - 8Lecture 1 Bonding forces:Ionic bonding Covalent bonding Metallic bonding Non-bonding forces:Dispersion forcesDipole-dipole attraction Ion-dipole attractionHydrogen bondingIonic Bonding:*opposite charges attractCoulomb’s Law:Lattice Energy: the energy released when one mole of an ionic compound is formed from its ions in the gas phase.Covalent Bonding:= Chemical bonds made by sharing electrons between the atoms making the bondsDispersion Forces:Fluctuations in the electron distribution in atoms and molecules result in a temporary dipole.– Region with excess electron density has partial (–) charge.– Region with depleted electron density has partial (+) charge.The attractive forces caused by these temporary dipoles are called dispersion forces.– They are also known as London forces or van der Waals forces.– As a temporary dipole is established in one molecule, it induces a dipole in all the surrounding molecules.*All molecules and atoms will have dispersion forces.Dipole–Dipole Attractions: Interactions between Polar Molecules:Polar molecules have a permanent dipole.– Bond polarity and molecular geometry (shape) determine the substances polarity– Dipole momentThe permanent dipole adds to the attractive forces between the molecules, raising the boiling and melting points relative to nonpolar molecules of similar size and shape.Hydrogen Bonding: A Special Case of Dipole–Dipole Interaction:When a very electronegative atom is bonded to hydrogen, it strongly pulls the bonding electrons toward it.O—H, N—H, or F—HBecause hydrogen has no other electrons, when its electron is pulled away, the nucleus becomes deshielded, exposing the H proton.The exposed proton acts as a very strong center of positive charge, attracting all the electron clouds from neighboring molecules.Hydrogen bonds are very strong intermolecular attractive forces.Stronger than dipole–dipole or dispersion forcesSubstances that can hydrogen bond will have higher boiling points and melting points than similar substances that cannot.But hydrogen bonds are not nearly as strong as chemical bonds. (2–5% the strength of covalent bonds)Lecture 2: Ion–Dipole Attraction:In a mixture, ions from an ionic compound are attracted to the dipole of polar molecules.The strength of the ion–dipole attraction is one of the main factors that determine the solubility of ionic compounds in water.Intermolecular Forces:Dispersion forces have the following characteristics:– They are the weakest of the intermolecular attractions.– They are present in all molecules and atoms.– Their magnitude increases with molar mass.Polar molecules– have dipole–dipole attractive forces.Hydrogen bondsare– a type of dipole–dipole interaction;– the strongest of the intermolecular attractive forces a pure substance can have;– present when a molecule has H directly bonded to either O, N, or F atoms. (The only example of H bonded to F is HF).Ion–dipole attractionsare– present in mixtures of ionic compounds with polar molecules;– the strong intermolecular attractions;– especially important in aqueous solutions of ionic compounds.Attractive Forces and Solubility:Solubility depends, in part, on the attractive forces of the solute and solvent molecules.– Like dissolves like.– Miscible liquids will always dissolve in each other.Polar substances dissolve in polar solvents.Nonpolar molecules dissolve in nonpolar solvents.Many molecules have both hydrophilic and hydrophobic parts.– Solubility in water becomes a competition between the attraction of the polar groups for the water and the attraction of the nonpolar groups for their own kind.Immiscible Liquids:Pentane, C5H12, is a nonpolar molecule, and water is a polar molecule.The attractive forces between the water molecules are much stronger than the attractions of the water molecules for the pentane molecules.The result is that the liquids are immiscible.Surface TensionSurface tension is a property of liquids that results from the tendency of liquids to minimize their surface area.To minimize their surface area, liquids form drops that are spherical.– As long as there is no gravity The layer of molecules on the surface behaves differently than that on the interior, because the cohesive forces on the surface molecules have a net pull into the liquid interior.The surface layer acts like an elastic skin, allowing you to “float” a paper clip even though steel is denser than water.Because they have fewer neighbors to attract them, the surface molecules are lessstable than those in the interior.– They have a higher potential energy.The surface tension of a liquid is the energy required to increase the surface area a given amount.– Surface tension ofH2O = 72.8 mJ/m2• At room temperature– Surface tension ofC6H6 = 28 mJ/m2Factors Affecting Surface Tension:The stronger the intermolecular attractive forces, the higher the surface tension will be.Raising the temperature of a liquid reduces its surface tension.• Raising the temperature of the liquid increases the average kinetic energy of the molecules.• The increased molecular motion makes it easier to stretch the surface.Viscosity:the resistance of a liquid to flow.Factors Affecting Viscosity:The stronger the intermolecular attractive forces, the higher the liquid’s viscosity will be.The more spherical the molecular shape, the lower the viscosity will be.• Molecules roll more easily.• Less surface-to-surface contact lowers attractions.Raising the temperature of a liquid reduces its viscosity.• Raising the temperature of the liquid increases the average kinetic energyof the molecules.• The increased molecular motion makes it easier to overcome the intermolecular attractions and flow.Capillary Action:is the ability of a liquid to flow up a thin tube against the influence of gravity.– The narrower the tube, the higher the liquid rises.Capillary action is the result of two forces—cohesive and adhesive—working in conjunction. Cohesive forces hold the liquid molecules together.Adhesive forces attract the outer liquid molecules to the tube’s surface.Meniscus:The curving of the liquid surface in a thin tube is due to the competition between adhesive and cohesive forces.The meniscus of water is concave in a glass tube because water’s adhesion to the glass isstronger than its cohesion for itself.The meniscus of mercury is convex in a glass