Some Properties of a Liquid

1. Some Properties of a Liquid Surface Tension: The resistance to an increase in its surface area (strong forces between molecules lead to strong surface tension). Capillary Action: Spontaneous rising of a liquid in a narrow tube. (polar liquids) Viscosity: Resistance to flow (molecules with large intermolecular forces).

2. A molecule in the interior of a liquid is attracted by the molecules surrounding it, whereas a molecule at the surface of a liquid is attracted only by molecules below it and on each side.

3. Nonpolar liquid mercury forms a convex meniscus in a glass tube, whereas polar water forms a concave meniscus. adhesive cohesive

4. Types of Solids Crystalline Solids: highly regular arrangement of their components [table salt (NaCl), pyrite (FeS2)]. Amorphous solids: considerable disorder in their structures (glass).

5. crystalline solids: pyrite amethyst

6. Representation of Components in a Crystalline Solid Lattice: A 3-dimensional system of points designating the centers of components (atoms, ions, or molecules) that make up the substance.

7. Representation of Components in a Crystalline Solid Unit Cell: The smallest repeating unit of the lattice. • simple cubic (sc) • body-centered cubic (bcc) • face-centered cubic (fcc)

9. Crystalline silver contains cubic closest packed silver atoms.

10. The net number of spheres in a face-centered cubic unit cell= (6× 1/2) + (8 × 1/8) = 4 spheres

11. 1/8 atom corner 1 atom unit cell a 2 Simple Cubic Unit Cell x 8 corners = atoms in contact along edge (a)  a = 2r or r = V = a3 = 8r3

12. 1/8 atom corner Body-Centered Cubic Unit Cell x 8 corners = 1 atom + center = 1 atom 2 atoms/cell atoms in contact along body diagonal (D)

13. 1/2 atom face 1/8 atom corner Face-Centered Cubic Unit Cell x 8 corners = 1 atom x 6 faces = 3 atoms 4 atoms/cell atoms in contact along face diagonal (d) or

14. X-ray crystallography:determination of the crystal structure of a solid

15. Reflection of X rays of wavelength  from a pair of atoms in two different layers of a crystal.

16. Bragg Equation Used for analysis of crystal structures. n = 2d sin  d = distance between atoms n = an integer  = wavelength of the x-rays

17. Types of Crystalline Solids Ionic Solid: contains ions at the points of the lattice that describe the structure of the solid (NaCl). Molecular Solid: discrete covalently bondedmolecules at each of its lattice points (sucrose, ice). Atomic Solid: there are 3 types of atomic solids: group 8A, metallic, and network

18. Examples of three types of crystalline solids. (a) An atomic solid. (b) An ionic solid. (c) A molecular solid.

19. Atomic Solids: • Group 8A: Noble gases. The forces that hold this solid together are london-dispersion forces • Metallic Solids: have a special type of nondirectional delocalized bonding • Network Solids: Form a network by using covalent directional localized bonds

20. Metallic Solids Type of atomic solidsThe electron sea model for metals postulates a regular array of cations in a "sea" or gas of valence electrons. Group 1 A Group 2 A

21. Network Solids: a type of atomic solids Composed of strong directional covalent bondsthat are best viewed as a “giant molecule”. • brittle • do not conduct heat or electricity • carbon, silicon-based graphite, diamond, ceramics, glass

22. Graphite consists of layers of carbon atoms.

23. Quartz The structure of quartz (empirical formula SiO2). Quartz contains chains of SiO4 tetrahedral (bottom) that share oxygen atoms.

25. Vaporization or Evaporation: A process by which liquid molecules escape from the surface of the liquid to the gaseous state. Endothermic Process ∆Hvaporization = enthalpy of vaporization or heat of vaporization > 0 is the energy required to vaporize 1 mol of a liquid. e.g., water, ∆Hvaporization = 40.7 kJ/mol

26. The rates of condensation and evaporation over time for a liquid sealed in a closed container.

27. Equilibrium Vapor Pressure or vapor pressure: • It is the pressure exerted by the vapor in equilibrium with the liquid at a certain temperature- • It depends on:  The temperature of the liquid as T increases, VP increases  The strength of intermolecular forces as forces increase, VP decreases

28. Measuring the vapor pressure of a liquid- Vapor pressure increases when the strength of the intermolecular forces decreases

29. The dependence of vapor pressure on the temperature of the liquid. As T increases there is a greater fraction of molecules with enough kinetic energy to overcome the intermolecular forces and escape from the liquid to the vapor phase

31. Hvap log (Pvap) = - (1/T) + C 2.303R Dependence of VP on temperature: Clausius-Clapeyron Equation:

32. The vapor pressure of water, ethanol, and diethyl ether as a function of temperature. Plots of In(Pvap) versus 1/T (Kelvin temperature) for water, ethanol, and diethyl ether.

33. Solids also have a vapor pressure. Sublimation: change of state from solid to gas state Iodine being heated, causing it to sublime, onto an evaporating dish cooled by ice.

34. Defining Melting and Boiling Points: • Normal Melting Point: is defined as the temperature at which the solid and liquid states have the same vapor pressure under conditions where the total pressure is 1 atm. If the word “normal” is not used then the pressure has to be specified. • Normal Boiling Point: is the temperature at which the vapor pressure of the liquid is exactly 1 atmosphere. If the word “normal” is not used, then the pressure has to be specified

35. The heating curve (not drawn to scale) for a given quantity of water where energy is added at a constant rate.

36. At the temperature of transition: • For example (s)  (l) or (l)  (g); the temperature does not change, the KE does not change: • But you are heating—Where is the heat going? • The answer: it is going to overcome the intermolecular forces- that is into the potential energy of the system instead of kinetic energy

37. The Phase Transition: Melting or Fusion: (s) (l) Tm : Melting Point Tf: Freezing Point Boiling or condensation: (l) (g) Tb:Boiling Point ∆HFusion > 0 (energy in, endo) ∆Hvaporization > 0 (energy in, endo)

39. Melting Point: The liquid and Solid States have equal vapor pressures Normal Melting Point: the liquid and solid states have equal vapor pressures at 1 atm external pressure

40. SUPERCOOLING: water not freezing at the melting point exactly

41. Possible BUMPING: Boiling chip releasing air bubbles acts as a nucleating agent for the bubbles that form when water boils.

42. Water in a closed system with a pressure of 1 atm exerted on the piston. No bubbles can form within the liquid as long as the vapor pressure is less than 1 atm.

43. Phase Diagrams • A phase diagram: is a representation of the phases of a substance as a function of temperature and pressure- • It describes conditions and events in a closed system, where no material can escape to the surroundings and no air is present.

44. The phase diagram for water

45. An area: one phase • A line: separating 2 areas, 2 phases in equilirium • The triple point: the temperature and pressure at which the 3 phases are in equilibrium (s) ↔ (l) ↔ (g) [there is one triple point for water, intersection of 3 lines each line represents an equilibrium between 2 phases] For water: it is 0.01 oC and 4.58 torr (0.0060 atm) • Critical point: the critical temperature is defined as the temperature above which the vapor cannot be liquefied no matter what pressure is applied. The critical pressure is required to produce a liquid at the critical temperature. For water: it is 374 oC and 218 atm

46. Experiment 1: P is 1 atm. Begin with a cylinder filled with ice at -20o C Normal Melting point, and Normal Boiling point Experiment 2: P is 2.0 torr. Start with ice as the only component at -20o C. At -10oC Sublimation takes place as you heat Experiment 3: Pressure is 4.58 torr. Start with ice at -20 oC. The triple point is reached before the gaseous state is formed. Experiment 4: Pressure is 225 atm. Start with liq. water at 300oC. The liquid goes into an intermediate Fluid region—once you are beyond the critical point for water.

48. The meaning of the negative Slope of the s ↔ l line for water This signifies that: density of liquid > density of ice volume of liquid < volume of ice Reason: Hydrogen bonding in liquid Hexagonal structure in ice Not allowing close proximity

49. Hexagonal Structure of ice: does not allow close hydrogen bonding as much as in liquid water This gives the solid a larger volume than the liquid

50. The phase diagram for carbon dioxide.