Chapter 11. Liquids and Solids

11.1 Properties of Liquids 1. Liquids assume the shape of their container, but Chapter 11: Liquids and Solids 11.2 Intermolecular Forces (IMF)  BONDS hold atoms together within a single molecule. (Polar and nonpolar covalent bonds)  Review polar and nonpolar bonds and molecules  INTERMOLECULAR FORCES (IMF) hold molecules together in liquids and solids.  IMF are always weaker than bonds! have a constant volume. 2. Different liquids flow at different rates. 3. Liquids are not compressible since the atoms/molecules are close together. 4. Liquids have much higher densities than gases. 5. Soluble liquids will mix uniformly together. Bonds vs IMF In one HCl molecule what holds the H to the Cl is a polar covalent bond. H-Cl In a sample with thousands of HCl molecules what holds them together is IMF. H-Cl H-Cl Intermolecular Forces London Dispersion Forces IMF are attractions between + and - charges between molecules.  Temporary attraction between nonpolar molecules or 1) London Dispersion Forces (LDF)  Electrons pushed to one side result in a temporary 2) Dipole-Dipole Forces (DD) 3) Hydrogen Bond Forces (HB) H bond forces is NOT a bond!!! atoms that form when two of them get real close. partial negative charge (-) that disappears when the molecules separate.  Often seen in gases since very little attraction between nonpolar molecules – thus they are not close together but far apart (gas)!!!  Bigger molecules, more electrons, more London Force. 1 Dipole-Dipole Forces Dipole-Dipole Forces  Exists between polar molecules (have partial + and – ends).  The partial + end of one molecule is attracted to the partial - end of a second molecule (opposites attract). + + H Dipole-Dipole Forces  Stronger than London forces. Cl H - Cl Hydrogen Bond Forces  An especially strong dipole force between molecules containing the very polar H-F, H-O or H-N bonds.  Only with POLAR molecules.  The + H end of one molecule is attracted to the - F/O/N end of a second molecule. Hydrogen Bond Forces  Strongest type of IMF, yet still much weaker than a bond. Intermolecular Forces Indicate the strongest type of IMF between these molecules: Polar or Nonpolar? Polar covalent bonds Strongest Intermolecular Force CO2 PF3 HF CH4 2 Bonds vs. IMF  Opposite charges attract according to Coulomb’s Law.  Bonds  Ionic bond (holds metal/nonmetal ions together)  Polar Covalent Bond (e- shared unequally between nonmetal atoms)  Nonpolar Covalent Bond (e- shared equally)  Forces  The electrostatic attraction between two charges is proportional to the charge magnitude (q) and inversely proportional to the distance (r) squared.  F = ke(q1q2 / r2)  Larger charge and smaller ions = stronger attraction!  Ionic bonds very strong because charges are complete  London (nonpolar molecules)  Dipole Dipole (polar molecules)  H bond Force (H bonded to F, O, or N) Bonds vs. IMF Bond or IMF? Coulomb’s Law Review What holds these together??? What holds the atoms together in one ammonia NH3 molecule? +1, +2, +3 charges. Like in NaCl.  Dipole-dipole IMF much weaker cause charges are much less than +1 (only partial charges, + and  -) 11.3 Vapor Pressure (VP)  Vapor Pressure is the pressure exerted by gas molecules above a liquid in a closed container. What is holding the H and O atoms together in water? What is holding three HCl molecules together? What is holding the ions together in salt NaCl. What is holding four H2O molecules together. What holds nitrogen gas molecules to each other? What is holding the O’s together in an oxygen gas molecule? What is holding two ammonia molecules together? Answers on Next Slide Vapor Pressure  Does a molecule with stronger IMF have a higher or lower VP ???  Lower. Stronger attractions mean less likely to break away from surface and go into gas state (so less gas so less pressure). Which has weaker IMF? Higher VP?  At the surface of a liquid some molecules have enough kinetic energy to break the attractive forces (IMF) with neighboring molecules.  They escape from the liquid and go into the gas state.  If no lid, they float away with air molecules.  If there is a lid, a pressure develops. Vapor Pressure Balloons are attached to flasks containing water and ether. Which has stronger IMF? Higher VP? Water has stronger IMF and it stays together as liquid. Ether has low IMF, molecules break away into gas filling balloon, so it has higher VP. 3 Boiling Point (BP) Surface Tension Boiling point is the temperature at which a liquid changes to gas.  Surface molecules hold on to each other, this is Stronger IMF = higher or lower bp??  Stronger IMF = high or low surface tension? Surface Tension Which drop of liquid has higher IMF & surface tension? why liquids make drops / beads. Viscosity The resistance of a liquid to flow.  Oil flows slowly  high viscosity  Vodka flows rapidly  low viscosity Stronger IMF  higher or lower viscosity ??? Review – Properties of Liquids Let’s compare ammonia and fluorine. First what IMF do they have? Which has stronger IMF? Which has the lower bp? Which is polar? Which has higher VP? Which is least viscous (if liquid)? Which has more surface tension? Review – Properties of Liquids Fill in the blanks with increase or decrease As IMF increase: Viscosity ____________ Boiling point ___________ Surface tension ___________ Vapor pressure ___________ 4 11.4 Properties of Solids 11.5 Crystalline Solids  Solids have a fixed shape and volume.  Solids are crystalline or noncrystalline.  Solids are not compressible - particles are close together.  Most solids have a slightly higher density than their liquid state. Solids sink in their liquid.  Ice is an important exception since ice is actually less dense than water. Ice floats in water.  Solids do not mix by diffusion or osmosis. • Solid arranged in Glucose a specific order. • Crystalline solids have regular geometric shapes / patterns (i.e., hexagonal) Quartz Cu Emerald Solids Ionic Molecular Metallic Particles mp & bp Other properties metal cations & nonmetal anions High hard, brittle, some soluble in water, conduct electricity when melted or dissolved in water nonmetal atoms or molecules Low usually insoluble in water, do not conduct electricity metal atoms surrounded by "sea of electrons" Varies malleable, ductile, insoluble in most liquid solvents, conduct electricity Ex. Ice Salt NaCl KCl AgBr CaF2 MgCl2 S8 Dry ice Copper silver zinc 11.6 Heating Curve Heating Curve gas l  g bp T (C) Type liquid mp s  l solid Heat Added  5 Phase Changes 11.7 Structure of Water  The temperature stays constant.  All the energy goes into breaking the IMF (not the bonds).  Thus when you boil / melt / freeze / condense a substance you are breaking or forming the IMF, not the bonds. 11.8 Properties of Water • Very polar, high IMF • Low vapor pressure • Unusually High bp & mp: bp=100C, mp=0C • High surface tension • Water expands as it freezes  Density of ice is less than density of liquid water (very rare!) • Other elements that do this are: silicon, H2O has a bent molecular geometry with a bond angle less than 109.5  1. Water has very polar O-H bonds: can dissolve many ionic compounds and mix with other polar substances. 2. Water has strong H bond Forces between molecules. Interesting Facts  Solubility of a gas in a liquid increases as P increases, and decreases as P decreases  When you open soda can, you decrease the pressure, and some CO2 gas comes out of solution as bubbles (solubility of gas decreased). gallium, germanium, antimony, bismuth, plutonium Ch. 11 Self-Test, p. 339  Try 1-5, 7-8, 12-14  Answers in Appendix J 6