Chapter 10Liquids and Solids

Intermolecular Forces

Forces between (rather than within) molecules. dipole-dipole attraction: molecules with

dipoles orient themselves so that “+” and “” ends of the dipoles are close to each other.

hydrogen bonds: dipole-dipole attraction in which hydrogen is bound to a highly electronegative atom (F, O, N).

Figure 10.2. Dipole-Dipole Attractions

Figure 10.3. A Water Molecule

Figure 10.4. The Boiling Points of the Covalent Hydrides of the Elements in Groups 4A, 5A, 6A, and 7A

London Dispersion Forces

relatively weak forces that exist among noble gas atoms and nonpolar molecules. (Ar, C8H18)

caused by instantaneous dipole, in which electron distribution becomes asymmetrical.

the ease with which electron “cloud” of an atom can be distorted is called polarizability.

Figure 10.5. London Dispersion Forces

Types of Solids

• Crystalline Solids: highly regular arrangement of their components [table salt (NaCl), pyrite (FeS2)]. Crystalline solid produces the beautiful characteristic shapes of crystals.

• Amorphous solids: considerable disorder in their structures (glass). Although glass is a solid, a great deal of disorder exists in its structure.

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.

Unit Cell: The smallest repeating unit of the lattice.

• simple cubic• body-centered cubic• face-centered cubic

Figure 10.9. Three Cubic Unit Cells and the Corresponding Lattices

Types of Crystalline Solids

• Ionic Solid: contains ions at the points of the lattice that describe the structure of the solid (NaCl). When NaCl dissolves in water, Na+ and Cl- ions are distributed throughout the resulting solution.

• Molecular Solid: discrete covalently bonded molecules at each of its lattice points (sucrose, ice). Sugar is composed of neutral molecules that are dispersed throughout the water when the solid dissolves.

• Atomic Solid: Atoms at the lattice points that describe the structure of the solid (graphite, diamond, fullerenes).

Figure 10.12. Examples of Three Types of Crystalline Solids

Metal AlloysSubstances that have a mixture of elements and metallic properties.1. Substitutional Alloy: some metal atoms replaced by others of similar size.brass = Cu/Zn (one third Cu replaced by Zn)2. Interstitial Alloy: Interstices (holes) in closest packed metal structure are occupied by small atoms.

steel = iron + carbon3. Both types: Alloy steels contain a mix of substitutional (carbon) and interstitial (Cr, Mo) alloys.

Figure 10.21. Two Types of Alloys

Network Solids

Composed of strong directional covalent bonds that are best viewed as a “giant molecule”.

• brittle• do not conduct heat or electricity• carbon, silicon-based

graphite, diamond, ceramics, glass

Figure 10.22. The Structures of Diamond and Graphite

Figure 10.26. The Structure of Quartz

Figure 10.27. Silicate Anions

Vapor Pressure

is the pressure of the vapor present at equilibrium.

is determined principally by the size of the intermolecular forces in the liquid.

increases significantly with temperature.

Volatile liquids have high vapor pressures. Heat of vaporization (Hvap.): The energy

required to vaporize 1 mole of a liquid at a pressure of 1 atm. Vaporization is an endothermic process.

Figure 10.38. Behavior of a Liquid in a Closed Container

Figure 10.39. The Rates of Condensation and Evaporation

Melting Point

• Temperature at which the solid and liquid states have the same vapor pressure under conditions where the total pressure is 1 atmosphere.

• Molecules break loose from lattice points and solid changes to liquid. (Temperature is constant as melting occurs.)

vapor pressure of solid = vapor pressure of liquid

Boiling Point

• The temperature at which the vapor pressure of the liquid is exactly 1 atmosphere.

• Constant temperature when added energy is used to vaporize the liquid.

vapor pressure of liquid = pressure of surrounding

atmosphere

Phase Diagram• Represents phases of a substance as a function

of temperature and pressure.

• Critical temperature: temperature above which the vapor can not be liquefied.

• Critical pressure: pressure required to liquefy AT the critical temperature.

• Critical point: critical temperature and pressure (for water, Tc = 374°C and 218 atm).

• Triple point: all three states of water are present.

Figure 10.50. The Phase Diagram for Water