Intermolecular Forces March 5, 2018 Intermolecular Forces Geometry and Bonding Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

DO NOW (4 MIN) March 5, 2018 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions Do Now: (on your DO Now Sheet) Determine whether the following is polar, ionic, or nonpolar: NH4+ NH3 CO CO2 H2O Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Heat of Vap and Heat of Fusion March 5, 2018 H2O (s)  H2O(l) H fus= 6.02 kJ/mol H2O (l)  H2O(g) H vap= 40.7 kJ/mol Where is more energy needed? Why is more energy needed? Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Heat of Vap and Heat of Fusion March 5, 2018 Particle diagrams of the three states of matter What can you say about the attraction between molecules? Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Intramolecular and Intermolecular Bonds March 5, 2018 Bonds and intermolecular forces have one very fundamental thing in common, both are electrostatic forces of attractions. The primary difference between bonds and intermolecular forces is the locations of the attraction and the magnitudes of the attraction. Intermolecular Forces Definition: Intermolecular Forces are electrostatic forces of attraction that exist between an area of negative charge on one molecule and an area of positive charge on a second molecule. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Intramolecular and Intermolecular Bonds March 5, 2018 Three types of intramolecular bonding: Ionic Covalent Metallic Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Intramolecular and Intermolecular Bonds March 5, 2018 In pairs, provide an example of each: Ionic Covalent Metallic Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Ch. 11 - Intermolecular Forces March 5, 2018 The forces holding solids and liquids together are called intermolecular forces. Intermolecular forces are much weaker than ionic or covalent bonds. Example: 16 kJ/mol to vaporize HCl compared to 431 kJ/mol to break HCl into its elements. When a substance melts or boils, the intermolecular forces are broken (not the covalent bonds). Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Intermolecular Forces March 5, 2018 Boiling point reflects intermolecular force strength. - A high boiling point indicates strong attractive forces. - A high melting point also reflects strong attractive forces. There are 4 basic types of intermolecular forces… 1) ion-dipole forces 2) dipole-dipole forces 3) London dispersion forces 4) hydrogen bonding…(a special type of dipole force) Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Na+ and Cl- ions dissolved in water. Ion-Dipole Forces March 5, 2018 http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf Interaction between an ion and a dipole. Strongest of all intermolecular forces. Na+ and Cl- ions dissolved in water. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Dipole-Dipole Forces Exist between neutral polar molecules. March 5, 2018 Exist between neutral polar molecules. Weaker than ion-dipole forces. If two molecules have about the same mass and size, then dipole-dipole forces increase with increasing polarity. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

London Dispersion Forces March 5, 2018 http://chemsite.lsrhs.net/FlashMedia/html/dipoleVsLondon.html London dispersion forces exist between all molecules! A temporary, instantaneous dipole may be created by an uneven distribution of electrons around the nucleus (nuclei) of an atom (molecule). London dispersion forces arise due to the Coulombic interaction of the temporary dipole with the electron distribution in neighboring atoms and molecules…(One temporary dipole can create another one!) “instantaneous dipoles” Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

London Dispersion Forces March 5, 2018 The larger the molecule (the greater the number of electrons) the “more polarizable” or the easier it is to create instantaneous dipoles. London dispersion forces increase as molecular weight increases. The differences in LDF strength explains why some halogens are gases at room temperature while others are liquid or solid. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

London Dispersion Forces March 5, 2018 London dispersion forces also depend on the shape of the molecule. The greater the surface area available for contact, the greater the dispersion forces. London dispersion forces between spherical nonpolar molecules are lower than the forces between long nonpolar molecules. less surface area, less force Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Hydrogen Bonding A special case of dipole-dipole forces. March 5, 2018 A special case of dipole-dipole forces. By experiments, the boiling pts. of compounds with H-F, H-O, and H-N bonds are abnormally high. The intermolecular forces are therefore abnormally strong. H-bonding requires… H bonded to a small, highly electronegative element (most important for compounds of F, O, and N) 2) an unshared electron pair on a nearby small highly electronegative ion or atom (usually F, O, or N on another molecule). Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Hydrogen Bonding Examples March 5, 2018 abnormally high B.P. 1) polar molecules 2) nonpolar molecules 3) Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Hydrogen Bonding in DNA March 5, 2018 Hydrogen Bonding in DNA Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Try It March 5, 2018 Determine the following types of intermolecular forces involved: Could be more than one! NH3 with NH3 CO2 with CO2 H2O with CaCl2 C2H4 with C2H4 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Try It March 5, 2018 In each pair, determine which compound has a higher boiling point: NH3 or NH4+ CO2 or CO C2H4 with C3H8 CHALLENGE: H2O or CaCl2 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Try It Which of the following demonstrate Hydrogen bonding: NH3 CH4 March 5, 2018 Which of the following demonstrate Hydrogen bonding: NH3 CH4 CH2O C2H3OH NH4+ Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Dissolving and IMF’s “Like Dissolves Like” March 5, 2018 “Like Dissolves Like” Polar solutes dissolve in polar solvents (or nonpolar dissolves in nonpolar.) Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

March 5, 2018 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Properties of Liquids Liquids vary in viscosity. March 5, 2018 Liquids vary in viscosity. - Viscosity is the resistance of a liquid to flow. The “thicker” the liquid, the more viscosity. The stronger the intermolecular forces, the higher the viscosity. Typically, as temperature increases, viscosity decreases. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Properties of Liquids Explain the statement: March 5, 2018 Explain the statement: Typically, as temperature increases, viscosity decreases. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Properties of Liquids Surface Tension -Acts as a thin skin. March 5, 2018 Surface Tension -Acts as a thin skin. The stronger the intermolecular forces, the greater the surface tension. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

(1) “Soap makes water wetter” by reducing the surface tension. Fun Facts March 5, 2018 (1) “Soap makes water wetter” by reducing the surface tension. (2) Soap doesn’t kill germs. Instead, the germs are attracted to the soap suds and are washed down the drain. Normally, oil and water don't mix, so they separate into two different layers. Soap breaks up the oil into smaller drops, which can mix with the water. It works because soap is made up of molecules with two very different ends. One end of the soap molecules is polar – they are hydrophilic. The other end of the soap molecues is nonpolar - they are hydrophobic. The hydrophobic ends of soap molecules attach to the oil. The hydrophilic ends stick out into the water. This causes a drop of oil to be suspended in the water. This is how soap cleans your hands - it causes drops of grease and dirt to be pulled off your hands and suspended in water. These drops are washed away when you rinse your hands. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Fun Facts - SOAP Video - SOAP March 5, 2018 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Phase Changes & Energy March 5, 2018 Generally, it will take more heat to vaporize a liquid than to melt a solid… (∆H(vap) > ∆H(fusion) ) Why? - Every intermolecular bond is broken when vaporizing, but only some of the intermolecular forces break when melting solids. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Liquefying Gases March 5, 2018 Gases can be liquefied by increasing pressure at some temperature. - Critical temperature: the highest temperature at which a substance can remain a liquid regardless of the pressure applied. - Critical pressure: the pressure needed at the critical temperature. Notice: As intermolecular attractions increase, critical temp, & pressure increase. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Vapor Pressure and Boiling Liquids March 5, 2018 Some of the molecules on the surface of a liquid have enough energy to escape the attraction of the liquid. These molecules move into the gas phase. As the number of molecules in the gas phase increases, some of the gas phase molecules strike the surface and return to the liquid. After some time the pressure of the gas will be constant at the vapor pressure. Dynamic Equilibrium: the point when as many molecules escape the surface as strike the surface. Vapor pressure is the pressure exerted when the liquid and vapor are in dynamic equilibrium. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Vapor Pressure and Boiling Liquids March 5, 2018 Liquids boil when the external pressure equals the vapor pressure. Temperature of the boiling point increases as pressure increases. Normal boiling point is the boiling point at 760 mmHg (1 atm). A substance with a high vapor pressure is said to be volatile. It readily evaporates. A substance with more intermolecular forces has a lower vapor pressure and therefore a higher B.P. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

March 5, 2018 (a) Measuring vapor of a liquid by using a simple barometer. (b) The water vapor pushed the mercury level down. (c) Diethyl ether shows a higher vapor pressure than water. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Vapor Pressure and Boiling Liquids March 5, 2018 Two ways to get a liquid to boil: 1) increase temperature 2) decrease pressure (vacuum pump) Pressure cookers operate at high pressure. - At high pressure the boiling point of water is higher than at 1 atm. - Therefore, there is a higher temperature at which the food is cooked, reducing the cooking time required. Boiling points increase with molecular weight as long (as the intermolecular forces are similar.) - Example: CH4 (m.w. = 16) < C2H6 (m.w. = 30) < C3H8 (m.w. = 44) [ lowest B.P.] [highest B.P.] Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Pressure Cooker Volcanic Vent March 5, 2018 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Autoclave: Steam Sterilizer Using High Pressure March 5, 2018 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Phase Diagrams March 5, 2018 Shows the relationship between the 3 phases of matter at various temperatures and pressures. Triple Point: All 3 phases of matter at equilibrium. Critical Point: The highest temperature at which the liquid phase can exist. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Phase Diagrams of H2O and CO2 March 5, 2018 Notice the slope of the solid–liquid equilibrium line. This indicates that water expands when it freezes and CO2 contracts when it freezes. Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Phase Diagram of H2O Regular Temp. & Pressure March 5, 2018 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Pair Work Complete the worksheet in pairs. March 5, 2018 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions

Exit Ticket (4 min) Answer on a separate sheet of paper: March 5, 2018 Exit Ticket (4 min) Answer on a separate sheet of paper: Which has a greater melting point: CaCl2 or NaCl H3CF or CH4 Learning Target: I can determine the relationship between intermolecular forces and boiling point, vapor pressure, viscosity, surface tension, and interactions