1. Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Introductory Chemistry, 3 rd Edition Nivaldo Tro Chapter 12 Liquids, Solids, and Intermolecular Forces 2009, Prentice Hall

2. Tro's Introductory Chemistry, Chapter 12 2 Interactions Between Molecules Many of the phenomena we observe are related to interactions between molecules that do not involve a chemical reaction, such as taste, smell at the receptor sites in our tongue and nose, fleeting in nature.

3. Tro's Introductory Chemistry, Chapter 12 3 Interactions Between Molecules Important to scientists are the physical properties of solids, liquids and gas: How can water exists in three states on this planet Why are there solids What holds a liquid together Why are gasses not liquids Why does matter have such different melting and boiling points

4. Tro's Introductory Chemistry, Chapter 12 4 The Physical States of Matter Matter can be classified as solid, liquid, or gas based on what properties it exhibits. Fixed = Keeps shape when placed in a container. Indefinite = Takes the shape of the container.

5. Tro's Introductory Chemistry, Chapter 12 5 Structure Determines Properties The atoms or molecules have different structures in solids, liquids, and gases, leading to different properties.

6. Tro's Introductory Chemistry, Chapter 12 6 Properties of the States of Matter: Gases Low densities compared to solids and liquids. Fluid. The material exhibits a smooth, continuous flow as it moves. Take the shape of their container(s). Expand to fill their container(s). Can be compressed into a smaller volume.

7. Tro's Introductory Chemistry, Chapter 12 7 Properties of the States of Matter: Liquids High densities compared to gases. Fluid. The material exhibits a smooth, continuous flow as it moves. Take the shape of their container(s). Keep their volume, do not expand to fill their container(s). Cannot be compressed into a smaller volume.

8. Tro's Introductory Chemistry, Chapter 12 8 Properties of the States of Matter: Solids High densities compared to gases. Nonfluid. They move as an entire “block” rather than a smooth, continuous flow. Keep their own shape, do not take the shape of their container(s). Keep their own volume, do not expand to fill their container(s). Cannot be compressed into a smaller volume.

9. Tro's Introductory Chemistry, Chapter 12 9 The Structure of Solids, Liquids, and Gases

10. Tro's Introductory Chemistry, Chapter 12 10 Gases In the gas state, the particles have complete freedom from each other. The particles are constantly flying around, bumping into each other and their container(s). In the gas state, there is a lot of empty space between the particles. On average.

11. Tro's Introductory Chemistry, Chapter 12 11 Gases, Continued Because there is a lot of empty space, the particles can be squeezed closer together. Therefore, gases are compressible. Because the particles are not held in close contact and are moving freely, gases expand to fill and take the shape of their container(s), and will flow.

12. Tro's Introductory Chemistry, Chapter 12 12 Liquids The particles in a liquid are closely packed, but they have some ability to move around. The close packing results in liquids being incompressible. But the ability of the particles to move allows liquids to take the shape of their container and to flow. However, they don’t have enough freedom to escape and expand to fill the container(s).

13. Tro's Introductory Chemistry, Chapter 12 13 Solids The particles in a solid are packed close together and are fixed in position. Though they are vibrating. The close packing of the particles results in solids being incompressible. The inability of the particles to move around results in solids retaining their shape and volume when placed in a new container, and prevents the particles from flowing.

14. Tro's Introductory Chemistry, Chapter 12 14 Solids, Continued Some solids have their particles arranged in an orderly geometric pattern. We call these crystalline solids. Salt and diamonds. Other solids have particles that do not show a regular geometric pattern over a long range. We call these amorphous solids. Plastic and glass.

15. Tro's Introductory Chemistry, Chapter 12 15 Why Is Sugar a Solid, But Water Is a Liquid? The state a material exists in depends on the attraction between molecules and their ability to overcome the attraction. The attractive forces between ions or molecules depends on their structure. The attractions are electrostatic. They depend on shape, polarity, etc. The ability of the molecules to overcome the attraction depends on the amount of kinetic energy they possess.

16. Tro's Introductory Chemistry, Chapter 12 16 Properties and Attractive Forces PhaseDensityShapeVolume Relative strength of attractive forces GasLowIndefinite Weakest LiquidHighIndefiniteDefiniteModerate SolidHighDefinite Strongest

17. Tro's Introductory Chemistry, Chapter 12 17 Phase Changes: Melting Generally, we convert a material in the solid state into a liquid by heating it. Adding heat energy increases the amount of kinetic energy of the molecules in the solid. Eventually, they acquire enough energy to partially overcome the attractive forces holding them in place. This allows the molecules enough extra freedom to move around a little and rotate.

18. Tro's Introductory Chemistry, Chapter 12 18 Phase Changes: Boiling Generally, we convert a material in the liquid state into a gas by heating it. Adding heat energy increases the amount of kinetic energy of the molecules in the liquid. Eventually, they acquire enough energy to completely overcome the attractive forces holding them together. This allows the molecules complete freedom to move around and rotate.

19. Tro's Introductory Chemistry, Chapter 12 19 Properties of Liquids: Surface Tension Liquids tend to minimize their surface—a phenomenon we call surface tension. This tendency causes liquids to have a surface that resists penetration. The stronger the attractive force between the molecules, the larger the surface tension.

20. Tro's Introductory Chemistry, Chapter 12 20 Surface Tension Molecules in the interior of a liquid experience attractions to surrounding molecules in all directions. However, molecules on the surface experience an imbalance in attractions, effectively pulling them in. To minimize this imbalance and maximize attraction, liquids try to minimize the number of molecules on the exposed surface by minimizing their surface area. Stronger attractive forces between the molecules = larger surface tension.

21. Tro's Introductory Chemistry, Chapter 12 21 Properties of Liquids: Viscosity Some liquids flow more easily than others. The resistance of a liquid’s flow is called viscosity. The stronger the attractive forces between the molecules, the more viscous the liquid is. Also, the less round the molecule’s shape, the larger the liquid’s viscosity. Some liquids are more viscous because their molecules are long and get tangled in each other, causing them to resist flowing.

22. Tro's Introductory Chemistry, Chapter 12 22 Evaporation The evaporation happens at the surface. Molecules on the surface experience a smaller net attractive force than molecules in the interior. All the surface molecules do not escape at once, only the ones with sufficient kinetic energy to overcome the attractions will escape.

23. 23 Escaping the Surface The average kinetic energy is directly proportional to the Kelvin temperature. Not all molecules in the sample have the same amount of kinetic energy. Those molecules on the surface that have enough kinetic energy will escape. Raising the temperature increases the number of molecules with sufficient energy to escape.

24. Tro's Introductory Chemistry, Chapter 12 24 Escaping the Surface, Continued Since the higher energy molecules from the liquid are leaving, the total kinetic energy of the liquid decreases, and the liquid cools. The remaining molecules redistribute their energies, generating more high energy molecules. The result is that the liquid continues to evaporate.

25. Tro's Introductory Chemistry, Chapter 12 25 Factors Effecting the Rate of Evaporation Liquids that evaporate quickly are called volatile liquids, while those that do not are called nonvolatile. Increasing the surface area increases the rate of evaporation. More surface molecules. Increasing the temperature increases the rate of evaporation. Raises the average kinetic energy, resulting in more molecules that can escape. Weaker attractive forces between the molecules = faster rate of evaporation.

26. Tro's Introductory Chemistry, Chapter 12 26 Reconnecting with the Surface When a liquid evaporates in a closed container, the vapor molecules are trapped. The vapor molecules may eventually bump into and stick to the surface of the container or get recaptured by the liquid. This process is called condensation. A physical change in which a gaseous form is converted to a liquid form.

27. Tro's Introductory Chemistry, Chapter 12 27 Evaporation and Condensation Eventually, the condensation and evaporation reach the same speed. The air in the flask is now saturated with water vapor. Shortly, the water starts to evaporate. Initially the rate of evaporation is much faster than rate of condensation When water is just added to the flask and it is capped, all the water molecules are in the liquid. Opposite processes that occur at the same rate in the same system are said to be in dynamic equilibrium.

28. Tro's Introductory Chemistry, Chapter 12 28 Vapor Pressure Once equilibrium is reached, from that time forward, the amount of vapor in the container will remain the same. As long as you don’t change the conditions. The partial pressure exerted by the vapor is called the vapor pressure. The vapor pressure of a liquid depends on the temperature and strength of intermolecular attractions.

29. Tro's Introductory Chemistry, Chapter 12 29 Boiling In an open container, as you heat a liquid the average kinetic energy of the molecules increases, giving more molecules enough energy to escape the surface. So the rate of evaporation increases. Eventually, the temperature is high enough for molecules in the interior of the liquid to escape. A phenomenon we call boiling.

30. Tro's Introductory Chemistry, Chapter 12 30 Boiling Point The temperature at which the vapor pressure of the liquid is the same as the atmospheric pressure is called the boiling point. The normal boiling point is the temperature required for the vapor pressure of the liquid to be equal to 1 atm. The boiling point depends on what the atmospheric pressure is. The temperature of boiling water on the top of a mountain will be cooler than boiling water at sea level.

31. Tro's Introductory Chemistry, Chapter 12 31 Temperature and Boiling As you heat a liquid, its temperature increases until it reaches its boiling point. All the energy from the heat source is being used to overcome all of the attractive forces in the liquid.

32. Tro's Introductory Chemistry, Chapter 12 32 Energetics of Evaporation As it loses its high energy molecules through evaporation, the liquid cools. Then the liquid absorbs heat from its surroundings to raise its temperature back to the same as the surroundings. Processes in which heat flows into a system from the surroundings are said to be endothermic. As heat flows out of the surroundings, it causes the surroundings to cool. As alcohol evaporates off your skin, it causes your skin to cool.

33. Tro's Introductory Chemistry, Chapter 12 33 Energetics of Condensation As it gains the high energy molecules through condensation, the liquid warms. Then the liquid releases heat to its surroundings to reduce its temperature back to the same as the surroundings. Processes in which heat flows out of a system into the surroundings are said to be exothermic. As heat flows into the surroundings, it causes the surroundings to warm.

34. Tro's Introductory Chemistry, Chapter 12 34 Heat of Vaporization The amount of heat needed to vaporize one mole of a liquid is called the heat of vaporization.  H vap It requires 40.7 kJ of heat to vaporize one mole of water at 100 °C. Always endothermic.  Number is +.  H vap depends on the initial temperature. Since condensation is the opposite process to evaporation, the same amount of energy is transferred but in the opposite direction.  H condensation = −  H vaporization

35. Tro's Introductory Chemistry, Chapter 12 35 Heats of Vaporization of Liquids at Their Boiling Points and at 25 °C Liquid Chemical formula Normal boiling point, °C  H vap at boiling point, (kJ/mol)  H vap at 25 °C, (kJ/mol) Water H2OH2O100+40.7+44.0 Isopropyl alcohol C 3 H 7 OH82.3+39.9+45.4 Acetone C3H6OC3H6O56.1+29.1+31.0 Diethyl ether C 4 H 10 O34.5+26.5+27.1

36. Example 12.1—Calculate the Mass of Water that Can Be Vaporized with 155 KJ of Heat at 100 °C. Since the given amount of heat is almost 4x the  H vap, the amount of water makes sense. 1 mol H 2 O = 40.7 kJ, 1 mol = 18.02 g 155 kJ g H 2 O Check: Solution: Solution Map: Relationships: Given: Find: kJmol H 2 Og H 2 O

37. Tro's Introductory Chemistry, Chapter 12 37 Practice—How Much Heat Energy, in kJ, is Required to Vaporize 87 g of Acetone, C 3 H 6 O, (MM 58.08) at 25  C? (  H vap = 31.0 kJ/mol)

38. 38 Practice—How Much Heat Energy, in kJ, Is Required to Vaporize 87 g of Acetone, C 3 H 6 O, (MM 58.08) at 25  C? (  H vap = 31.0 kJ/mol), Continued Since the given mass is than one mole, the answer being greater than  H vap makes sense. 1 mol C 3 H 6 O = 31.0 kJ at 25  C, 1 mol = 58.08 g 87 g C 3 H 6 O kJ Check: Solution: Solution Map: Relationships: Given: Find: g C 3 H 6 Omol C 3 H 6 OkJ

39. Tro's Introductory Chemistry, Chapter 12 39 Temperature and Melting As you heat a solid, its temperature increases until it reaches its melting point. Once the solid starts to melt, the temperature remains the same until it all turns to a liquid. All the energy from the heat source is being used to overcome some of the attractive forces in the solid that hold them in place.

40. Tro's Introductory Chemistry, Chapter 12 40 Energetics of Melting and Freezing When a solid melts, it absorbs heat from its surroundings, it is endothermic. As heat flows out of the surroundings, it causes the surroundings to cool. As heat flows out of your drink into the ice cubes (causing them to melt), the liquid gets cooler. When a liquid freezes, it releases heat into its surroundings, it is exothermic. As heat flows into the surroundings, it causes the surroundings to warm. Orange growers often spray their oranges with water when a freeze is expected. Why?

41. Tro's Introductory Chemistry, Chapter 12 41 Heat of Fusion The amount of heat needed to melt one mole of a solid is called the heat of fusion.  H fus Fusion is an old term for heating a substance until it melts, it is not the same as nuclear fusion. Since freezing (crystallization) is the opposite process of melting, the amount of energy transferred is the same, but in the opposite direction.  H crystal = -  H fus In general,  H vap >  H fus because vaporization requires breaking all attractive forces.

42. Tro's Introductory Chemistry, Chapter 12 42 Heats of Fusion of Several Substances Liquid Chemical formula Melting point, °C  H fusion, (kJ/mol) Water H2OH2O0.006.02 Isopropyl alcohol C 3 H 7 OH-89.55.37 Acetone C3H6OC3H6O-94.85.69 Diethyl ether C 4 H 10 O-116.37.27

43. Tro's Introductory Chemistry, Chapter 12 43 Practice—How Much Heat Energy, in kJ, is Required to Melt 87 g of Acetone, C 3 H 6 O, (MM 58.08)? (  H fus = 5.69 kJ/mol)

44. 44 Practice—How Much Heat Energy, in kJ, Is Required to Melt 87 g of Acetone, C 3 H 6 O, (MM 58.08)?, Continued Since the given mass is more than one mole, the answer being greater than  H vap makes sense. 1 mol C 3 H 6 O = 5.69 kJ at -94.8  C, 1 mol = 58.08 g 87 g C 3 H 6 O kJ Check: Solution: Solution Map: Relationships: Given: Find: g C 3 H 6 Omol C 3 H 6 OkJ

45. Tro's Introductory Chemistry, Chapter 12 45 Sublimation Sublimation is a physical change in which the solid form changes directly to the gaseous form. Without going through the liquid form. Like melting, sublimation is endothermic.

46. Tro's Introductory Chemistry, Chapter 12 46 Intermolecular Attractive Forces

47. Tro's Introductory Chemistry, Chapter 12 47 Effect of the Strength of Intermolecular Attractions on Properties The stronger the intermolecular attractions are, the more energy it takes to separate the molecules. Substances with strong intermolecular attractions have higher boiling points, melting points, and heat of vaporization; they also have lower vapor pressures.

48. Tro's Introductory Chemistry, Chapter 12 48 Practice—Pick the Substance in Each Pair with the Stronger Intermolecular Attractions. sugar or water water or acetone ice or dry ice sugar or water. water or acetone. ice or dry ice.

49. 49 Attractive Forces and Properties Like dissolves like. Miscible = Liquids that do not separate, no matter what the proportions. 1.Ionic 2.Polar molecules dissolve in polar solvents. Water, alcohol, CH 2 Cl 2. 3.A special case of polarity: Molecules with O or N higher solubility in H 2 O due to H-bonding with H 2 O. 4.Nonpolar molecules dissolve in nonpolar solvents or Dispersion forces Ligroin (hexane), toluene, CCl 4. If molecule has both polar and nonpolar parts, then hydrophilic-hydrophobic competition.

50. Tro's Introductory Chemistry, Chapter 12 50 Dispersion Forces Also known as London forces or instantaneous dipoles. Caused by distortions in the electron cloud of one molecule inducing distortion in the electron cloud on another. Distortions in the electron cloud lead to a temporary dipole. The temporary dipoles lead to attractions between molecules—dispersion forces. All molecules have attractions caused by dispersion forces.

51. Tro's Introductory Chemistry, Chapter 12 51 Instantaneous Dipoles

52. Tro's Introductory Chemistry, Chapter 12 52 Strength of the Dispersion Force Depends on how easily the electrons can move, or be polarized. The more electrons and the farther they are from the nuclei, the larger the dipole that can be induced. Strength of the dispersion force gets larger with larger molecules.

53. Tro's Introductory Chemistry, Chapter 12 53 Dispersion Force and Molar Mass

54. Tro's Introductory Chemistry, Chapter 12 54 Practice—The Following Are All Made of Non– Polar Molecules. Pick the Substance in Each Pair with the Highest Boiling Point. CH 4 or C 3 H 8 BF 3 or BCl 3 CO 2 or CS 2 CH 4 or C 3 H 8. BF 3 or BCl 3. CO 2 or CS 2.

55. Tro's Introductory Chemistry, Chapter 12 55 Permanent Dipoles Because of the kinds of atoms that are bonded together and their relative positions in the molecule, some molecules have a permanent dipole. Polar molecules. The size of the molecule’s dipole is measured in debyes, D.

56. Tro's Introductory Chemistry, Chapter 12 56 Dipole-to-Dipole Attraction Polar molecules have a permanent dipole. A + end and a – end. The + end of one molecule will be attracted to the – end of another.

57. Tro's Introductory Chemistry, Chapter 12 57 Polarity and Dipole-to-Dipole Attraction

58. Tro's Introductory Chemistry, Chapter 12 58 Attractive Forces + - + - + - + + + + _ _ _ _ Dispersion forces—All molecules. Dipole-to-dipole forces—Polar molecules.

59. Tro's Introductory Chemistry, Chapter 12 59 Intermolecular Attraction and Properties All molecules are attracted by dispersion forces. Polar molecules are also attracted by dipole- dipole attractions. Therefore, the strength of attraction is stronger between polar molecules than between nonpolar molecules of the same size.

60. Tro's Introductory Chemistry, Chapter 12 60 CS 2 Nonpolar bonds = nonpolar molecule. CH 2 F 2 Polar bonds and asymmetrical = polar molecule. CF 4 Polar bonds and symmetrical shape = nonpolar molecule. Practice—Determine Which of the Following Has Dipole–Dipole Attractive Forces. (EN C= 2.5, F = 4, H = 2.1, S = 2.5) CS 2 CH 2 F 2 CF 4 

61. 61 Attractive Forces and Properties Like dissolves like. Miscible = Liquids that do not separate, no matter what the proportions. 1.Ionic 2.Polar molecules dissolve in polar solvents. Water, alcohol, CH 2 Cl 2. Molecules with O or N higher solubility in H 2 O due to H- bonding with H 2 O. 3.Nonpolar molecules dissolve in nonpolar solvents. Ligroin (hexane), toluene, CCl 4. If molecule has both polar and nonpolar parts, then hydrophilic-hydrophobic competition.

62. Tro's Introductory Chemistry, Chapter 12 62 Immiscible Liquids When liquid pentane, a nonpolar substance, is mixed with water, a polar substance, the two liquids separate because they are more attracted to their own kind of molecule than to the other.

63. Tro's Introductory Chemistry, Chapter 12 63 Hydrogen Bonding HF, or molecules that have OH or NH groups have particularly strong intermolecular attractions. Unusually high melting and boiling points. Unusually high solubility in water. This kind of attraction is called a hydrogen bond.

64. Tro's Introductory Chemistry, Chapter 12 64

65. Tro's Introductory Chemistry, Chapter 12 65 Properties and H-Bonding NameFormula Molar mass (g/mol) Structure Boiling point, °C Melting point, °C Solubility in water EthaneC2H6C2H6 30.0-88-172 Immiscible EthanolCH 4 O32.064.7-97.8 Miscible

66. Tro's Introductory Chemistry, Chapter 12 66 Intermolecular H-Bonding

67. Tro's Introductory Chemistry, Chapter 12 67 Hydrogen Bonding When a very electronegative atom is bonded to hydrogen, it strongly pulls the bonding electrons toward it. Since hydrogen has no other electrons, when it loses the electrons, the nucleus becomes deshielded. Exposing the proton. The exposed proton acts as a very strong center of positive charge, attracting all the electron clouds from neighboring molecules.

68. Tro's Introductory Chemistry, Chapter 12 68 H-Bonds vs. Chemical Bonds Hydrogen bonds are not chemical bonds. Hydrogen bonds are attractive forces between molecules. Chemical bonds are attractive forces that make molecules.

69. Tro's Introductory Chemistry, Chapter 12 69 Attractive Forces and Properties

70. Tro's Introductory Chemistry, Chapter 12 70 formaldehyde, CH 2 O 30.03 g/mol polar molecule  dipole – dipole attractions present  polar C=O bond & asymmetric fluoromethane, CH 3 F 34.03 g/mol polar molecule  dipole – dipole attractions present  polar C−F bond & asymmetric hydrogen peroxide, H 2 O 2 34.02 g/mol polar molecule  dipole – dipole attractions present  polar H−O bonds & asymmetric H−O bonds  Hydrogen bonding present formaldehyde, CH 2 O. 30.03 g/mol. polar molecule  dipole–dipole attractions present.  Polar C=O bond and asymmetric. fluoromethane, CH 3 F. 34.03 g/mol. polar molecule  dipole–dipole attractions present.  Polar C−F bond and asymmetric. hydrogen peroxide, H 2 O 2 34.02 g/mol. polar molecule  dipole–dipole attractions present.  Polar H−O bonds and asymmetric. H−O bonds  hydrogen-bonding present. Example 12.5—Which of the Following Is a Liquid at Room Temperature? (The Other Two Are Gases.)

71. Tro's Introductory Chemistry, Chapter 12 71 Practice–Pick the Compound in Each Pair Expected to Have the Higher Solubility in H 2 O. CH 3 CH 2 OCH 2 CH 3 or CH 3 CH 2 CH 2 CH 2 CH 3. CH 3 CH 2 NHCH 3 or CH 3 CH 2 CH 2 CH 3. CH 3 CH 2 OH or CH 3 CH 2 CH 2 CH 2 CH 2 OH.

72. Tro's Introductory Chemistry, Chapter 12 72 Practice–Pick the Compound in Each Pair Expected to Have the Higher Solubility in H 2 O, Continued. CH 3 CH 2 OCH 2 CH 3 or CH 3 CH 2 CH 2 CH 2 CH 3 contains polar O. CH 3 CH 2 NHCH 3 or CH 3 CH 2 CH 2 CH 3 contains polar N. CH 3 CH 2 OH or CH 3 CH 2 CH 2 CH 2 CH 2 OH contains less nonpolar parts.

73. Types of Intermolecular Forces Type of force Relative strength Present inExample Dispersion force Weak, but increases with molar mass All atoms and molecules H2H2 Dipole– Dipole force Moderate Only polar molecules HCl Hydrogen Bond Strong Molecules having H bonded to F, O, or N HF

74. Tro's Introductory Chemistry, Chapter 12 74 Crystalline Solids

75. Tro's Introductory Chemistry, Chapter 12 75 Types of Crystalline Solids

76. Tro's Introductory Chemistry, Chapter 12 76 Molecular Crystalline Solids Molecular solids are solids whose composite units are molecules. Solid held together by intermolecular attractive forces. Dispersion, dipole-dipole, or H-bonding. Generally low melting points and  H fusion.

77. Tro's Introductory Chemistry, Chapter 12 77 Ionic Crystalline Solids Ionic solids are solids whose composite units are formula units. Solid held together by electrostatic attractive forces between cations and anions. Cations and anions arranged in a geometric pattern called a crystal lattice to maximize attractions. Generally higher melting points and  H fusion than molecular solids. Because ionic bonds are stronger than intermolecular forces.

78. Tro's Introductory Chemistry, Chapter 12 78 Atomic Crystalline Solids Atomic solids are solids whose composite units are individual atoms. Solids held together by either covalent bonds, dispersion forces, or metallic bonds. Melting points and  H fusion vary depending on the attractive forces between the atoms.

79. Tro's Introductory Chemistry, Chapter 12 79 Practice—Classify Each of the Following Crystalline Solids as Molecular, Ionic, or Atomic. H 2 O(s) Si(s) C 12 H 22 O 11 (s) CaF 2 (s) Sc(NO 3 ) 3 (s) H 2 O(s)—molecular. Si(s)—atomic. C 12 H 22 O 11 (s)—molecular. CaF 2 (s)—ionic. Sc(NO 3 ) 3 (s)—ionic.

80. Tro's Introductory Chemistry, Chapter 12 80 Types of Atomic Solids: Metallic Metallic solids are held together by metallic bonds. Metal atoms release some of their electrons to be shared by all the other atoms in the crystal. The metallic bond is the attraction of the metal cations for the mobile electrons. Often described as islands of cations in a sea of electrons.

81. 81 Metallic Bonding The model of metallic bonding can be used to explain the properties of metals. The luster, malleability, ductility, and electrical and thermal conductivity are all related to the mobility of the electrons in the solid. The strength of the metallic bond varies, depending on the charge and size of the cations, so the melting points and  H fusion of metals vary as well.