1. Intermolecular Forces and States of Matter AP Chemistry

2. Chemical properties are related only to chemical composition; physical properties are related to chemical composition AND the physical state of the substance at the time. H2OH2O

3. intermolecular forces (IMFs): -- largely determine the physical properties of molecular liquids and solids forces between molecules GASES LIQUIDS SOLIDS << Solids w /highly-ordered structures are crystalline. covalent ionic and metallic STRENGTH OF IMFs…

4. Boiling (or freezing) doesn’t affect these Intermolecular Forces (IMFs) -- these are much weaker than ionic or covalent bonds -- In vaporizing water, we overcome the IMFs between water molecules, but... NOT the bonds holding the molecule together. (< 15% as strong) H H O

5. State of matter is determined by two opposing influences. HIGH MEDIUM LOW WEAK MEDIUM “STRONG” Temp. affects… -- BP and FP/MP depend on IMFs solid If KE of particles is… andIMFs are… liquid gas then the state of matter is… Pres. affects… KE IMFs (proximity) strong IMFs  high BP, high MP/FP weak IMFs  low BP, low MP/FP

6. Types of IMFs When ions are present: ion-dipole forces For neutral molecules: dipole-dipole forces London dispersion forces hydrogen bonding forces electrostatic forces There are different bonds between people: parent/child, boss/employee, friends, lovers, etc. We’re not talking about bonds holding an individual together.

7. KCl solution is given intravenously in cases of capital punishment by lethal injection. The KCl causes the heart muscle cells to cease contracting. Ion-Dipole Forces (IDFs) -- exist between an ion and a partial charge on the end of a polar molecule (i.e., a dipole) -- important for... solutions of ionic substances in polar liquids e.g., aq. soln. of KCl… K + H H O Cl – IDF “momentary kissage”

8. Dipole-Dipole Forces (DDFs) -- exist between neutral polar molecules that are close together -- weaker than IDFs -- as the dipole moment  (i.e., the polarity) increases... DDFs (thus, BP and MP ) Phosphine (PH 3 ), is used in pest control fumigation due to its high toxicity. In the liquid phase, phosphine is subject to DDFs.

9. London Dispersion Forces (LDFs) -- exist between all molecules, but are the ONLY forces between nonpolar molecules that are close together -- motion of e – causes instantaneous dipoles, which induce dipoles on nearby m’cules; LDFs with increasing molar mass -- polarizability: the ease with which the charge distribution in a molecule can be distorted by an external magnetic field -- large atoms w /lots of e – exhibit high polarizability

10. Hydrogen Bonding Forces (HBFs) -- -- exist between a hydrogen atom in a polar bond and an unshared electron pair on a nearby, small, highly electronegative ion or atom strongest IMF; special class of DDF (e.g., F, O, N, Cl) “bare proton” of H is attracted to unshared e – pairs; its small size allows close proximity/strong bond -- important in structures of proteins and DNA 3.0 Cl 4.0 F 3.5 O 3.0 N 2.8 Br 2.5 C S 2.1 P 2.4 Se

11. HBFs act between water/ice molecules. water ice O HH O HH O HH O HH O HH O HH O HH O HH O HH O HH O HH O HH Water expands 9% when it freezes.

12. Some Properties of Liquids viscosity: a liquid’s resistance to flow -- high viscosity = high resistance to flow -- depends on IMFs --as temp. increases, viscosity decreases

13. Molecules on a liquid’s surface experience a net inward force -- this reduces surface area and “packs together” m’cules on surface surface tension: the energy required to increase a liquid’s surface area by 1 m 2 -- water has a high surface tension due to HBFs a measure of the “tightness” of a surface’s “skin”

14. cohesive forces: IMFs that bind... adhesive forces: IMFs that bind... similar m’cules to each other a substance to a surface -- their relative magnitude determines the shape of a meniscus adhesion cohesion >< meniscus: H 2 Omeniscus: Hg

15. capillary action: the rise of liquids up narrow tubes -- adhesion _________ the liquid, while cohesion… “stretches” keeps it together In green plants, capillary action draws water through narrow tubes, collectively called xylem.

16. Why does liquid go up narrow tubes farther than up thick tubes? adhesion force 2  r  r 2 = Liquid stops rising under this condition. gravity If tube diameter increases by a factor of 10: adhesion increases 10X; liquid’s weight increases 100X.

17. Will a “plug” of liquid continue inching its way up a tube? As soon as plug breaks free from rest of liquid, “down” adhesion forces appear, which equal “up” adhesion forces. But there’s also gravity, so “down” wins. Assume there is a plug that wants to break free… “No creeping plugs.” Adhesion forces pull it up. Plug drops until “up” adhesion equals gravity.

18. Phase Changes (i.e., changes of state) -- energy changes required are related to IMFs -- melting, freezing, boiling (vaporization), condensation, sublimation, deposition (Evaporation?) heat of fusion (c f ): energy per “something” required to melt a substance -- also called... latent heat heat of vaporization (c v ): energy per “something” required to boil a substance passive process; room temp. or “fuse”or condense

19. How do magnitudes of c v and c f compare? > IMFs must be completely overcome (i.e., “broken”) KE must be increased enough to allow particles to slide, relative to each other (IMFs still in effect)

20. Heating curves are graphs of temperature v. heat added (or heat removed). -- specific heat capacity: energy req’d to change temp. of 1 _____ of a substance 1 o C (1 K) -- molar heat capacity: energy req’d to change temp. of 1 _____ of a substance 1 o C (1 K) Temp. Heat Added or Removed BP MP/FP  H = q = m c p  T  H = q = + / – m c x Within a phase: Between phases: gram mole Typical Heating Curve for a Pure Substance

21. Phase Change Constants for Water c p,ice = 2.077 J/g-K c f = 333 J/g c p,water = 4.18 J/g-K c v = 2256 J/g c p,wv = 2.042 J/g-K Find the enthalpy change when 82.4 g of ice at –13.5 o C turns to water at 72.8 o C. warm ice to 0 o C: q = m c p  T q = 82.4 (2.077) (0 – –13.5) q = 2310 J melt ice at 0 o C: q = m c f q = 82.4 (333)= 27439 J heat water from 0 o C to 72.8 o C: q = m c p  T q = 82.4 (4.18) (72.8 – 0)= 25075 J q tot =  H = 54.8 kJ

22. supercooling: temporarily cooling a liquid below its freezing point without it forming a solid -- critical temperature: the highest temperature at which a substance can be a liquid critical pressure: the pressure required to bring about liquefaction at the critical temp. heat is removed so quickly that particles have no time to assume an ordered structure as IMFs increase, crit. temp…increases The intersection of the critical temperature and the critical pressure is called the critical point.

23. Pressure cookers raise the con- fining pressure on the water, so the water boils at a higher temp. A substance’s vapor pressure is the pressure exerted by a vapor in dynamic equilibrium with its liquid or solid phase. -- as IMFs increase, VP... -- as temperature increases, VP... -- liquids that evaporate easily are said to be ______ (these have high VPs) -- boiling occurs when…VP = external pressure (usually from atmos.) -- normal boiling point (NBP): the boiling temp. of a liquid at 1 atm of pres. volatile

24. Phase Diagrams -- graphs showing the conditions under which equilibria exist between different states of matter T P SOLID LIQUID GAS 1 atm Phase Diagram for a Typical Substance critical point (CT, CP) NBPNFP/NMP triple point v.p. curve of liquid v.p. curve of solid changes in FP/MP

25. Water is NOT a typical substance. Its phase diagram differs slightly, as shown below. T P SOLID LIQUID GAS 1 atm Phase Diagram for Water supercritical fluid: how we describe a substance at or beyond its critical point s.c.f.

26. Structures of Solids amorphous solid: the particles have no orderly structure -- e.g., rubber, glass -- IMFs are highly variable, so these solids have no specific… MP

27. crystalline solid: the particles are in well-defined arrangements -- e.g., ionic and elemental metallic solids -- these melt at VERY specific temps. crystal lattice: a 3-D array of points showing the crystal’s structure The crystal lattice of sodium chloride (NaCl).

28. unit cells: the repeating units of a crystalline solid primitive (or simple) cubic body-centered cubic face-centered cubic 1 atom unit cell 2 atoms unit cell 4 atoms unit cell “continuous atomage”

29. Gold exhibits a face-centered cubic unit cell that is 4.08 A on a side. Estimate gold’s density, in g/cm 3. D = m V = 4 atoms (197.0 amu/at.) (4.08 A) 3 = 1.16 x 10 25 1x10 –8 cm amu cm 3 ( 1 g 6.02 x 10 23 amu ) = 19.3 g cm 3

30. close-packed layer. Roughly equal-sized spheres, such as those in metallic solids, are arranged in one of several configurations. These configurations are collectively called the close packing of spheres. -- In a given layer, the atoms are arranged such that each atom in that layer is surrounded by six others. This is called a...

31. ------ C cubic close packing hexagonal close packing Name of Pattern ------ A 1 (bottom) ------ B 2 ------ A 3 ------ B 4 (top) close-packed layer position close-packed layer position Layer Number ** Cubic close packing is equivalent to the face-centered cubic unit cell. (HCP)(CCP/FCC)

32. HCP: The coordination number for a packing pattern is equal to the number of equidistant, nearest neighbors for any atom within the matrix. -- for particular packing arrangements: CCP/FCC: BCC:P/SC: 12 86 X X X X For unequal-sized spheres, sometimes the larger spheres assume a close-packed arrangement, and then the smaller particles fit into the spaces in between.