13.3 The Nature of Solids > 1 Objectives: 1.Compare/contrast properties of solids to liquids and gases. 2.Give details about what happens during freezing, melting, and sublimation. 3.Interpret phase diagrams. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

13.3 The Nature of Solids > 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A Model for Solids In most solids, the atoms, ions, or molecules are packed tightly together. The general properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles. A Model for Solids

13.3 The Nature of Solids > 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A Model for Solids Tightly packed particles Dense and not easy to compress Particles vibrate in fixed points, so solids do not flow Properties of solids reflect the orderly arrangement fixed locations of their particles.

13.3 The Nature of Solids > 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A Model for Solids When you heat a solid, its particles vibrate more rapidly as their kinetic energy increases. The melting point (mp) is the temperature at which a solid changes into a liquid.

13.3 The Nature of Solids > 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A Model for Solids When you heat a solid, its particles vibrate more rapidly as their kinetic energy increases. The melting point (mp) is the temperature at which a solid changes into a liquid. –vibrations become strong enough to overcome the attractions that hold them.

13.3 The Nature of Solids > 6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A Model for Solids The freezing point (fp) is the temperature at which a liquid changes into a solid. The melting and freezing points of a substance are at the same temperature.

13.3 The Nature of Solids > 7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A Model for Solids The freezing point (fp) is the temperature at which a liquid changes into a solid. The melting and freezing points of a substance are at the same temperature. At that temperature, the liquid and solid phases are in equilibrium. Solid Liquid melting freezing

13.3 The Nature of Solids > 8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A Model for Solids In general, ionic solids have high melting points because relatively strong forces hold them together. –Sodium chloride, an ionic compound, has a rather high melting point of 801°C.

13.3 The Nature of Solids > 9 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A Model for Solids In general, ionic solids have high melting points because relatively strong forces hold them together. –Sodium chloride, an ionic compound, has a rather high melting point of 801°C. Molecular solids have relatively low melting points. –Hydrogen chloride, a molecular compound, melts at –112°C.

13.3 The Nature of Solids > 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Explain why solids do not flow, even though their particles are constantly moving.

13.3 The Nature of Solids > 11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Explain why solids do not flow, even though their particles are constantly moving. In a solid, the particles are packed tightly together and vibrate around fixed points. Even though the particles vibrate, they are limited in their movement and cannot flow.

13.3 The Nature of Solids > 12 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Crystal Structure and Unit Cells Allotropes Some substances can exist in more than one form.

13.3 The Nature of Solids > 13 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Crystal Structure and Unit Cells Allotropes In diamond, each carbon atom in the interior of the diamond is strongly bonded to four others. The array is rigid and compact. In graphite, the carbon atoms are linked in widely spaced layers of hexagonal arrays. In buckminster- fullerene, 60 carbon atoms form a hollow sphere. The carbons are arranged in penta- gons and hexagons.

13.3 The Nature of Solids > 14 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Crystal Structure and Unit Cells Allotropes The physical properties of diamond, graphite, and fullerenes are quite different. Diamond has a high density and is very hard. Graphite has a relatively low density and is soft and slippery. The hollow cages in fullerenes give them strength and rigidity.

13.3 The Nature of Solids > 15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Crystal Structure and Unit Cells Allotropes Diamond, graphite, and fullerenes are crystalline allotropes of carbon. Allotropes are two or more different molecular forms of the same element in the same physical state.

13.3 The Nature of Solids > 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Crystal Structure and Unit Cells Allotropes Diamond, graphite, and fullerenes are crystalline allotropes of carbon. Allotropes are two or more different molecular forms of the same element in the same physical state. Composed of atoms of the same element, but have different properties because their structures are different.

13.3 The Nature of Solids > 17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Crystal Structure and Unit Cells Allotropes Only a few elements have allotropes. In addition to carbon, these include phosphorus, sulfur, oxygen (O 2 and O 3 ), boron, and antimony.

13.3 The Nature of Solids > 18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What is the difference between an amorphous solid and a crystalline solid? Particles in a crystalline solid are arranged in an orderly, repeating pattern or lattice. Particles in an amorphous solid are arranged randomly.

13.3 The Nature of Solids > 19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.Sublimation SECTION 13.4 Sublimation The change of a substance from a solid to a vapor without passing through the liquid state is called sublimation. Sublimation can occur because solids, like liquids, have a vapor pressure.

13.3 The Nature of Solids > 20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.Sublimation Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature. Solid Vapor sublimation deposition

13.3 The Nature of Solids > 21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.Sublimation Sublimation has many useful applications. Solid carbon dioxide (dry ice) is often used as a coolant for goods such as ice cream, which must remain frozen during shipment.

13.3 The Nature of Solids > 22 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.Sublimation Sublimation has many useful applications. Solid carbon dioxide (dry ice) is often used as a coolant for goods such as ice cream, which must remain frozen during shipment. –Because it sublimes, it does not produce a liquid as ordinary ice does when it melts. –As it changes state, dry ice absorbs heat, keeping materials nearby cool and dry.

13.3 The Nature of Solids > 23 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Which of the following describes a solid undergoing sublimation? A.The vapor pressure exceeds the atmospheric pressure. B.The vapor pressure equals the atmospheric pressure. C.The vapor pressure is less than the atmospheric pressure. D.The vapor pressure is less than half the atmospheric pressure.

13.3 The Nature of Solids > 24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Which of the following describes a solid undergoing sublimation? A.The vapor pressure exceeds the atmospheric pressure. B.The vapor pressure equals the atmospheric pressure. C.The vapor pressure is less than the atmospheric pressure. D.The vapor pressure is less than half the atmospheric pressure.

13.3 The Nature of Solids > 25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Phase Diagrams The relationships among the solid, liquid, and vapor states (or phases) of a substance in a sealed container can be represented in a single graph. The graph is called a phase diagram. Phase Diagrams

13.3 The Nature of Solids > 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Phase Diagrams The relationships among the solid, liquid, and vapor states (or phases) of a substance in a sealed container can be represented in a single graph. The graph is called a phase diagram. –gives the temperature and pressure at which a substance exists as a solid, liquid, or gas (vapor).

13.3 The Nature of Solids > 27 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water. Interpret Graphs

13.3 The Nature of Solids > 28 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water. Interpret Graphs In each of the curving regions of the phase diagram, water is in a single phase.

13.3 The Nature of Solids > 29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water. Interpret Graphs The curving line that separates water’s vapor phase from its liquid phase describes the equilibrium conditions for liquid and vapor.

13.3 The Nature of Solids > 30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water. Interpret Graphs The other two lines describe the conditions for equilibrium between liquid water and ice and between water vapor and ice.

13.3 The Nature of Solids > 31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water. Interpret Graphs The point on the diagram at which all three lines meet is called the triple point.

13.3 The Nature of Solids > 32 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Phase Diagrams The triple point describes the only set of conditions at which all three phases can exist in equilibrium with one another.

13.3 The Nature of Solids > 33 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Phase Diagrams The triple point describes the only set of conditions at which all three phases can exist in equilibrium with one another. For water, the triple point is a temperature of 0.016°C and a pressure of 0.61 kPa.

13.3 The Nature of Solids > 34 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Phase Diagrams By referring to the phase diagram of water, you can determine what happens if you melt ice or boil water at pressures less than kPa. A decrease in pressure lowers the boiling point and raises the melting point. An increase in pressure will raise the boiling point and lower the melting point.

13.3 The Nature of Solids > 35 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Phase Diagrams Below the triple point, the vapor and liquid cannot exist in equilibrium. Increasing the pressure won’t change the vapor to a liquid. The solid and vapor are in equilibrium at temperatures below 0.016°C. With an increase in pressure, the vapor begins to behave more like a solid.