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Metallic and Ionic Solids Section 13.4. METALLIC AND IONIC SOLIDS 13.4 Table 13.6, gives a brief over view of various types of solids and the forces.

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Presentation on theme: "Metallic and Ionic Solids Section 13.4. METALLIC AND IONIC SOLIDS 13.4 Table 13.6, gives a brief over view of various types of solids and the forces."— Presentation transcript:

1 Metallic and Ionic Solids Section 13.4

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3 METALLIC AND IONIC SOLIDS 13.4 Table 13.6, gives a brief over view of various types of solids and the forces holding the unit together.Table 13.6, gives a brief over view of various types of solids and the forces holding the unit together. This table is a very good summary.This table is a very good summary. We will now consider crystal lattice solids.We will now consider crystal lattice solids.

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5 Network Solids Diamond Graphite

6 A comparison of diamond (pure carbon) with silicon. A comparison of diamond (pure carbon) with silicon.

7 Properties of Solids 1. Molecules, atoms or ions locked into a CRYSTAL LATTICE 2. Particles are CLOSE together 3. STRONG IM forces 4. Highly ordered, rigid, incompressible ZnS, zinc sulfide

8 Figure D model

9 Crystal Lattices and Unit Cells of Metal Atoms The crystal lattice is made up of unit cells, the smallest repeating unit of the solid structure.The crystal lattice is made up of unit cells, the smallest repeating unit of the solid structure. There are many different types of unit cells, but we will consider only the cubic unit cells.There are many different types of unit cells, but we will consider only the cubic unit cells. Figure 13.27the seven crystal system unit cells.Figure 13.27the seven crystal system unit cells.

10 Figure 13.27

11 Crystal Lattices Regular 3-D arrangements of equivalent LATTICE POINTS in space. The lattice points define UNIT CELLS, the smallest repeating internal unit that has the symmetry characteristic of the solid. There are 7 basic crystal systems, but we are only concerned with CUBIC.

12 Cubic Unit Cells All sides equal length All angles are 90 degrees

13 Unit Cells of Metal Atoms The three important cubic unit cells are:The three important cubic unit cells are: simple cubic (sc)simple cubic (sc) body-centered cubic (bcc)body-centered cubic (bcc) face-centered cubic (fcc).face-centered cubic (fcc).

14 Cubic Unit Cells Figure Metals have unit cells that are simple cubic (SC)simple cubic (SC) body centered cubic (BCC)body centered cubic (BCC) face centered cubic (FCC) or CCPface centered cubic (FCC) or CCP

15 Figure 13.28

16 Figure Corner Atom Face Atom

17 Simple cubic unit cell.Simple cubic unit cell. Note that each atom is at a corner of a unit cell and is shared among 8 unit cells.Note that each atom is at a corner of a unit cell and is shared among 8 unit cells. Simple Cubic Unit Cell Figure 13.28

18 Body-Centered Cubic Unit Cell

19 Definitions: for a Cube (x=y=z) face diagonal cell edge cell diagonal

20 Diagonal =4 atom radius =  3 edge BCC cell Body Diagonal WHY? 

21 face diagonal cell edge cell diagonal

22 Face Centered Cubic Unit Cell Atom at each cube corner plus atom in each cube face. Atom at each cube corner plus atom in each cube face. NOTE: FCC = CCP

23 Face diagonal ?

24 Crystal Lattices—Packing of Atoms or Ions Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible. Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible. FCC is more efficient than either BCC or SC. FCC is more efficient than either BCC or SC.

25 Page 541

26 Packing of C 60 molecules. Packing of C 60 molecules. They are arranged at the lattice points of a FCC lattice. They are arranged at the lattice points of a FCC lattice. Crystal Lattices—Packing of Atoms or Ions

27 Unit Cells of Metal Atoms Be sure to study Examples 13.6 and 13.7, and try Exercise 13.7 to develop skills in solving problems involving unit cells, density, atomic mass, and atomic radii.Be sure to study Examples 13.6 and 13.7, and try Exercise 13.7 to develop skills in solving problems involving unit cells, density, atomic mass, and atomic radii. Remember that in metallic solids the atoms touch along and edge or diagonal depending on the unit cell.Remember that in metallic solids the atoms touch along and edge or diagonal depending on the unit cell.

28 Finding the Lattice Type To find out if a metal is SC, BCC or FCC, use the known radius and density of an atom to calculate number of atoms per unit cell. To find out if a metal is SC, BCC or FCC, use the known radius and density of an atom to calculate number of atoms per unit cell. PROBLEM Al has density = g/cm 3 and Al radius = 143 pm. Verify that Al is FCC.

29 Finding the Lattice Type SOLUTION 1. Calculate unit cell volume (FCC) V = (cell edge) 3 Edge distance comes from face diagonal. Diagonal distance = √2 edge (Diagonal) 2 = 2 (edge) 2 Diag =  2 (edge) Therefore,

30 Finding the Lattice Type PROBLEM Al has density = g/cm 3 and Al radius = 143 pm. What is Al’s lattice type? SOLUTION Here diagonal = 4 radius of Al = 572 pm Therefore, edge = 572 pm /  2 = 404 pm In centimeters, edge = 4.04 x cm In centimeters, edge = 4.04 x cm So, V of unit cell = (4.04 x cm) 3 V = 6.62 x cm 3 V = 6.62 x cm 3

31 Finding the Lattice Type PROBLEM Al has density = g/cm 3 and Al radius = 143 pm. Verify that Al is FCC. SOLUTION 2. Use V and density to calculate mass of unit cell from DENSITY = MASS / VOL Mass = density volume = (6.62 x cm 3 )(2.699 g/cm 3 ) = 1.79 x g/unit cell

32 Finding the Lattice Type PROBLEM Al has density = g/cm 3 and Al radius = 143 pm. Verify that Al is FCC. SOLUTION 3. Calculate number of Al per unit cell from mass of unit cell. Mass 1 Al atom= g mol 1 mol x atoms 1 atom = x g, so 1.79 x g unit cell 1 atom x g = 3.99 Al atoms/unit cell 32

33 Number of Atoms per Unit Cell In the previous problem we calculated 4 Al atoms per unit cell. What does the cell look like? 1. Each corner Al is 1/8 inside the unit cell. 8 corners (1/8 Al per corner) = 1 net Al 8 corners (1/8 Al per corner) = 1 net Al 2. Each face Al is 1/2 inside the cell 6 faces (1/2 per face) = 3 net Al’s 6 faces (1/2 per face) = 3 net Al’s

34 FCC Number of Atoms per Unit Cell In the previous problem we calculated 4 Al atoms per unit cell. What does the cell look like? Repeatingunit

35 Number of Atoms per Unit Cell How many atoms in a SC, BCC or FCC?

36 SC Repeatingunit

37 BCC Repeatingunit

38 Number of Atoms per Unit Cell Unit Cell Type Net Number Atoms Unit Cell Type Net Number Atoms SC 1 SC 1 BCC2 BCC2 FCC4

39 Structures and Formulas of Ionic Solids Sodium chloride and cesium chloride are two common type ionic solids.Sodium chloride and cesium chloride are two common type ionic solids. The sodium chloride structure is FCC in Cl - with the sodium ions in the octahedral holes.The sodium chloride structure is FCC in Cl - with the sodium ions in the octahedral holes. The cesium chloride structure is simple cubic (SC) in Cl - with the cesium ion in the center hole.The cesium chloride structure is simple cubic (SC) in Cl - with the cesium ion in the center hole. Remember, the anion/cation ratio is determined by the chemical formula.Remember, the anion/cation ratio is determined by the chemical formula.

40 Simple Ionic Compounds Lattices of many simple ionic solids are built by taking a SC or FCC lattice of ions of one type and placing ions of opposite charge in the holes in the lattice. Lattices of many simple ionic solids are built by taking a SC or FCC lattice of ions of one type and placing ions of opposite charge in the holes in the lattice. EXAMPLE: CsCl has a SC lattice of Cs + ions with Cl - in the center. EXAMPLE: CsCl has a SC lattice of Cs + ions with Cl - in the center.

41 Simple Ionic Compounds CsCl has a SC lattice of Cs + ions with Cl - in the center. CsCl has a SC lattice of Cs + ions with Cl - in the center. 1 unit cell has 1 Cl - ion plus (8 corners)(1/8 Cs + per corner) = 1 net Cs + ion. = 1 net Cs + ion.

42 Figure 13.30

43 Simple Ionic Compounds Salts with formula MX can have SC structure — but not salts with formula MX 2 or M 2 X. Salts with formula MX can have SC structure — but not salts with formula MX 2 or M 2 X.

44 Simple Ionic Compounds Many common salts have FCC arrangements of anions with cations in OCTAHEDRAL HOLES — e.g., salts such as CA = NaCl Many common salts have FCC arrangements of anions with cations in OCTAHEDRAL HOLES — e.g., salts such as CA = NaCl FCC lattice of anions ----> 4 A - /unit cellFCC lattice of anions ----> 4 A - /unit cell C + in octahedral holes ---> 1 C + at centerC + in octahedral holes ---> 1 C + at center + [12 edges 1/4 C + per edge] = 4 C + per unit cell = 4 C + per unit cell 44

45 Figure 13.31

46 46

47 Ionic Lattice Page

48 The Sodium Chloride Lattice Na + ions are in OCTAHEDRAL holes in a face- centered cubic lattice of Cl - ions. Na + ions are in OCTAHEDRAL holes in a face- centered cubic lattice of Cl - ions.

49 Comparing NaCl and CsCl Even though their formulas have one cation and one anion, the lattices of CsCl and NaCl are different.Even though their formulas have one cation and one anion, the lattices of CsCl and NaCl are different. The different lattices arise from the fact that a Cs + ion is much larger than a Na + ion.The different lattices arise from the fact that a Cs + ion is much larger than a Na + ion.

50 Common Ionic Solids Titanium dioxide, TiO 2 Titanium dioxide, TiO 2 There are 2 net Ti 4+ ions and 4 net O 2- ions per unit cell. There are 2 net Ti 4+ ions and 4 net O 2- ions per unit cell.

51 Find the density of MgO Given: The structure is FCC in O 2- with Mg 2+ in the octahedral holesThe structure is FCC in O 2- with Mg 2+ in the octahedral holes Mg 2+ radius = 86 pmMg 2+ radius = 86 pm O 2- radius 126 pmO 2- radius 126 pm

52 CD

53 BCC

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55 See Examp &13.9, Exer & 13.9See Examp &13.9, Exer & 13.9 O.H. # 97 to det. the formula of perovskite.O.H. # 97 to det. the formula of perovskite.# 97# 97 Additional packing structures are given on page 623. The structure labeled CCP is just another name for FCC.Additional packing structures are given on page 623. The structure labeled CCP is just another name for FCC. O.H. B, #70 p, and # 71 p.O.H. B, #70 p, and # 71 p.O.H. BO.H. B For ionic unit cells, the ions of opposite charge (usually) touch along an edge or diagonal.For ionic unit cells, the ions of opposite charge (usually) touch along an edge or diagonal. See pages 621 for problem-solving tips.See pages 621 for problem-solving tips. Structures and Formulas of Ionic Solids

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57 Page 623

58 Common Ionic Solids Zinc sulfide, ZnSZinc sulfide, ZnS The S 2- ions are in TETRAHEDRAL holes in the Zn 2+ FCC lattice.The S 2- ions are in TETRAHEDRAL holes in the Zn 2+ FCC lattice. This gives 4 net Zn 2+ ions and 4 net S 2- ions.This gives 4 net Zn 2+ ions and 4 net S 2- ions.

59 Common Ionic Solids Fluorite or CaF 2Fluorite or CaF 2 FCC lattice of Ca 2+ ionsFCC lattice of Ca 2+ ions This gives 4 net Ca 2+ ions.This gives 4 net Ca 2+ ions. F - ions in all 8 tetrahedral holes.F - ions in all 8 tetrahedral holes. This gives 8 net F - ions.This gives 8 net F - ions.

60 13.5 MOLECULAR AND NETWORK SOLIDS Molecular solids are held together by relatively weak intermolecular forces.Molecular solids are held together by relatively weak intermolecular forces. –The molecules themselves may be made up of only a few atoms or up to 50 or 60 atoms. –The bonds between the atoms within the molecules are always covalent.

61 MOLECULAR AND NETWORK SOLIDS Network solids (Macromolecular) are made up of huge molecules having 10 5 or more atoms.Network solids (Macromolecular) are made up of huge molecules having 10 5 or more atoms. – Often the chunk we are looking at is one giant molecule!! Diamond and graphite are examples of this type of solid.Diamond and graphite are examples of this type of solid. – O.H. # 56 & # 75 and 3D models.

62 13.6 THE PHYSICAL PROPERTIES OF SOLIDS Some common properties of solids are:Some common properties of solids are: »melting point »heat of fusion »sublimation point The melting point is the temperature when the solid is in equilibrium with the liquid, normally at a pressure of 1 atm.The melting point is the temperature when the solid is in equilibrium with the liquid, normally at a pressure of 1 atm.

63 PHYSICAL PROPERTIES OF SOLIDS Heat of fusion or enthalpy of fusion, is the energy required to change one mole ( molar enthalpy of fusion) of the solid into the liquid.Heat of fusion or enthalpy of fusion, is the energy required to change one mole ( molar enthalpy of fusion) of the solid into the liquid. »The magnitudes of these properties can be linked to the intermolecular forces involved.

64 PHYSICAL PROPERTIES OF SOLIDS Sublimation is the direct change from solid to vapor without passing through the liquid state. For certain solids at room temperature and pressure, this is the normal transition.Sublimation is the direct change from solid to vapor without passing through the liquid state. For certain solids at room temperature and pressure, this is the normal transition. The enthalpy of sublimation corresponds to this process.The enthalpy of sublimation corresponds to this process.

65 The lattice energy is the energy required to convert the ionic solid to gaseous ions.The lattice energy is the energy required to convert the ionic solid to gaseous ions. Trends in lattice energies can be predicted using intermolecular forces.Trends in lattice energies can be predicted using intermolecular forces. O.H. Figure “13.39” and Table 13.7.O.H. Figure “13.39” and Table PHYSICAL PROPERTIES OF SOLIDS

66 Figure Enthalpies of Fusion

67 13.7 CHANGES IN STRUCTURE AND PHASE Phase diagrams can be used to illustrate the changes in phase that result from changes in temperature and pressure.Phase diagrams can be used to illustrate the changes in phase that result from changes in temperature and pressure. These diagrams contain the following 6 points of interest:These diagrams contain the following 6 points of interest: 1.triple point 2.normal boiling point 3.melting point 4.normal sublimation point 5.critical point 6.critical temperature

68 TRANSITIONS BETWEEN PHASES See the phase diagram for water, Figure Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line. (At equilibrium particles move from liquid to gas as fast as they move from gas to liquid, for example.)

69 Phase Diagrams There are three phases, and equilibrium exists between any two phases at the phase boundary.There are three phases, and equilibrium exists between any two phases at the phase boundary. There are two major classes of diagrams (1) Water and (2) carbon dioxide are most commonly used.There are two major classes of diagrams (1) Water and (2) carbon dioxide are most commonly used. In water the normal boiling point is present, the normal sublimation point is because the triple point is in front of the normal sublimation pointIn water the normal boiling point is present, the normal sublimation point is because the triple point is in front of the normal sublimation point

70 H2OH2OH2OH2O

71 71 TRANSITIONS BETWEEN PHASES As P and T increase, you finally reach the CRITICAL T and P As P and T increase, you finally reach the CRITICAL T and P (T C,P C ) Above critical T no liquid exists no matter how high the pressure.. LIQUID GAS P critical High Pressure High Temperature T critical Note that line goes straight up

72 CO 2 T3T3T3T3 TosTosTosTos T c, P c

73 73 Water Carbon dioxide

74 Phase Diagram for Water Animation of solid phase. Animation of solid phase.

75 Animation of equilibrium between solid and liquid phases. Animation of equilibrium between solid and liquid phases. Phase Diagram for Water

76 Animation of liquid phase. Animation of liquid phase. Phase Diagram for Water

77 Animation of equilibrium between liquid and gas phases. Animation of equilibrium between liquid and gas phases. Phase Diagram for Water

78 Animation of gas phase. Animation of gas phase. Phase Diagram for Water

79 Animation of equilibrium between solid and gas phases. Animation of equilibrium between solid and gas phases. Phase Diagram for Water

80 Animation of triple point. Animation of triple point. TRIPLE POINT At the TRIPLE POINT all three phases are in equilibrium. Phase Diagram for Water

81 Phases Diagrams— Important Points for Water T(  C) P(mmHg) T(  C) P(mmHg) Normal boil point Normal freeze point0 760 Triple point

82 TRANSITIONS BETWEEN PHASES As P and T increase, you finally reach the CRITICAL T and P As P and T increase, you finally reach the CRITICAL T and P (T C,P C ) Above critical T no liquid exists no matter how high the pressure.. LIQUID GAS P critical High Pressure High Temperature T critical Note that line goes straight up

83 Critical T and P COMPDT c ( o C)P c (atm) H 2 O H 2 O CO CO CH CH Freon (CCl 2 F 2 ) Freon (CCl 2 F 2 ) Notice that T c and P c depend on intermolecular forces. Notice that T c and P c depend on intermolecular forces.

84 Solid-Liquid Equilibria In any system, if you increase P the DENSITY will go up. Therefore — as P goes up, equilibrium favors phase with the larger density (or SMALLER volume/gram). Liquid H 2 OSolid H 2 O Liquid H 2 OSolid H 2 O Density1.00 g/cm g/cm 3 cm 3 /gram

85 Solid-Liquid Equilibria Solid H 2 O Liquid H 2 O P T 760 mmHg 0  C Normal freezing point LIQUID H 2 O ICE favored at low P favored at high P

86 Solid-Liquid Equilbria Raising the pressure at constant T causes water to melt. The NEGATIVE SLOPE of the S/L line is unique to H 2 O. Almost everything else has positive slope. P T freezing Solid H 2 O Liquid H 2 O 760 mmHg 0  C Normal point

87 Solid-Liquid Equilbria The behavior of water under pressure is an example of LE CHATELIER’S PRINCIPLE At Solid/Liquid equilibrium, raising P squeezes the solid. It responds by going to phase with greater density, i.e., the liquid phase. Solid H 2 O Liquid H 2 O P T 760 mmHg 0  C Normal freezing point

88 Solid-Vapor Equilibrium At P < 4.58 mmHg and T <  C solid H 2 O can go directly to vapor. This process is called SUBLIMATION This is how a frost-free refrigerator works. This is how a frost-free refrigerator works.

89 In a closed system … Questions 1.Can we change the equilibrium in this system? 2.Is there any reason for wanting to change the equilibrium in this system?

90 Frost-free freezers Air in the freezer is warmed then dried. The vapor pressure of ice is torr. Warm, desiccated air can remove water vapor.

91 PRESSUREPRESSURE WATER

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