In covalent solids, atoms are held together in an extensive three- dimensional network entirely by covalent bonds. Types of solids 12.4

In molecular solids, the lattice points are occupied by molecules; the attractive forces between them are van der Waals forces and/or hydrogen bonding. Types of Crystals

In metallic solids, every lattice point is occupied by an atom of the same metal. Electrons are delocalized over the entire crystal. Delocalized electrons make metals good conductors. Large cohesive force resulting from delocalization makes metals strong. Types of Crystals

Glass Amorphous solids lack a regular three-dimensional arrangement of atoms. Glass is an amorphous solid.

Amorphous Solids Crystalline quartz Noncrystalline (amorphous) quartz glass

Phase Changes A phase is a homogeneous part of a system that is separated from the rest of the system by a well defined boundary. When a substance goes from one phase to another phase, it has undergone a phase change. ExamplePhase Change Freezing of water H 2 O(l) → H 2 O(s) Evaporation (or vaporization) of water H 2 O(l) → H 2 O(g) Melting (fusion) of ice H 2 O(s) → H 2 O(l) Condensation of water vapor H 2 O(g) → H 2 O(l) Sublimation of dry ice CO 2 (s) → CO 2 (g) Deposition of iodine I 2 (g) → I 2 (s) 12.5

Phase Changes Breaking attractions ALWAYS requires the particles to absorb energy. Endothermic (+) Increase in Potential Energy Energy supplied by the surroundings often in the form of Kinetic Energy (collisions resulting from motion of the particles) Decrease in observed temperature Forming attractions, the particles ALWAYS release energy Exothermic (-) Decrease in Potential Energy Energy released into the surroundings often converted into the form of Kinetic Energy Increase in observed temperature

The six possible phase changes Phase Changes PE

The boiling point of a substance is defined as the temperature at which its vapor pressure equals the external atmospheric pressure. The molar heat of vaporization (ΔH vap ) is the amount of heat required to vaporize a mole of substance at its boiling point. Phase Changes

The transformation of a liquid to a solid is called freezing. The reverse process is called melting, or fusion. The melting point (freezing point) of a solid (or liquid) is the temperature at which the solid and liquid phases coexist in equilibrium. ice ⇌ water H 2 O(s) ⇌ H 2 O(l) In dynamic equilibrium, the forward and reverse process are occurring at the same rate. Phase Changes

The molar heat of fusion (ΔH fus ) is the energy required to melt 1 mol of a solid. Phase Changes

Heating curves: Activity: Describe what is happening to the kinetic and potential energy at each point on the graph above Phase Changes Solid Boiling point Vapor Liquid Solid and liquid in equilibrium Liquid and vapor in equilibrium Heat change for the substance Temperature Melting point

Sublimation is the process by which molecules go directly from the solid phase to the vapor phase. Deposition is reverse process of sublimation. The molar enthalpy of sublimation (ΔH sub ) of a substance is the energy required to sublime 1 mole of a solid. Phase Changes ΔH sub = ΔH fus + ΔH vap Solid I 2 in equilibrium with its vapor Text Practice:

Phase Diagrams A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas. The triple point is the only combination of pressure and temperature where three phases of a substance exist in equilibrium triple point

The phase diagram of water: Phase Diagrams

Worked Example 12.8 Using the following phase diagram, (a) determine the normal boiling point and the normal melting point of the substance, (b) determine the physical state of the substance at 2 atm and 110°C, and (c) determine the pressure and temperature that correspond to the triple point of the substance.

Worked Example 12.8 (cont.) Solution By drawing lines corresponding to a given pressure and/or temperature, we can determine the temperature at which a phase change occurs, or the physical state of the substance under specified conditions. (a) The normal boiling and melting points are ~140°C and ~205°C, respectively.

Worked Example 12.8 (cont.) Solution (b) At 2 atm and 110°C the substance is a solid.

Worked Example 12.8 (cont.) Solution (c) The triple point occurs at ~0.8 atm and ~115°C.

Study Guide for Sections DAY 19, Terms to know: Sections phase, phase change, boiling point, molar heat of a process, melting point, heat of fusion, heating curve, sublimation, deposition, phase diagram DAY 19, Specific outcomes and skills that may be tested on exam 3: Sections Be able to describe and explain the differences between covalent, molecular, ionic, and metallic solids and the differences between crystals and amorphous solids Given a molecular formula or Lewis structure, be able to predict whether the molecules will form a covalent, molecular, ionic, or metallic solid and a crystalline or amorphous solid Be able to give examples of each of the 6 phase changes discussed Be able to predict and explain temperature and heat changes for any of the phase changes or areas between phase changes on a heating curve Given a phase diagram, be able to label the areas of solid, liquid, and gas, determine the state of matter at a given temperature and pressure and be able to find the melting point, boiling point, and triple point Be able to draw a phase diagram and label each of the three sections of the diagram

Extra Practice Problems for Sections Complete these problems outside of class until you are confident you have learned the SKILLS in this section outlined on the study guide and we will review some of them next class period

Prep for Day 20 Must Watch videos: (molarity, Tyler DeWitt) (molarity, Tyler DeWitt) (dilution, thechemistrysolution) (molality, Tyler DeWitt) (molality II, Tyler DeWitt) (balancing, crash course chemistry) (mole ratios, Tyler DeWitt) (balancing, Bozeman) Other helpful videos: (concentration units, Isaacs) (molarity, thechemistrysolution) (concentrations, Bozeman) (molality problems, Tyler DeWitt) (UC-Irvine, lectures 13) Read Sections 9.5 (pages ), 13.3, 8.1, 8.3, 11.8