Slide 1 : Intermolecular Forces and
Liquids and Solids Chapter 11
Slide 2 : A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary. 2 Phases Solid phase - ice Liquid phase - water 11.1
Slide 3 : Intermolecular Forces 11.2 Intermolecular forces are attractive forces between molecules. Intramolecular forces hold atoms together in a molecule. Intermolecular vs Intramolecular
41 kJ to vaporize 1 mole of water (inter)
930 kJ to break all O-H bonds in 1 mole of water (intra) “Measure” of intermolecular force
boiling point
melting point
DHvap
DHfus
DHsub
Slide 4 : Types of Intermolecular Forces 1. Hydrogen Bond (strongest) 11.2 The hydrogen bond is a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. IT IS NOT A BOND. A & B are N, O, or F
Slide 5 : Hydrogen Bond 11.2
Slide 6 : Why is the hydrogen bond considered a “special” dipole-dipole interaction? 11.2
Slide 7 : Types of Intermolecular Forces 2. Ion-Dipole Forces Attractive forces between an ion and a polar molecule 11.2
Slide 8 : 11.2
Slide 9 : Types of Intermolecular Forces 3. Dipole-Dipole Forces Attractive forces between polar molecules 11.2
Slide 10 : Types of Intermolecular Forces 4. Dispersion Forces – van der Walls forces/London forces (weakest) Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules 11.2 ion-induced dipole interaction dipole-induced dipole interaction
Slide 11 : Intermolecular Forces 4. Dispersion Forces Continued 11.2 Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted. Polarizability increases with:
greater number of electrons
more diffuse electron cloud
Slide 12 : What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH4 CH4 is nonpolar: dispersion forces. SO2 SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules. 11.2
Slide 13 : Properties of Liquids Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area. Strong intermolecular forces High surface tension 11.3
Slide 14 : Properties of Liquids Cohesion is the intermolecular attraction between like molecules 11.3 Adhesion is an attraction between unlike molecules Cohesion attracted to glass attracted to each other
Slide 15 : Properties of Liquids Viscosity is a measure of a fluid’s resistance to flow. 11.3 Strong intermolecular forces High viscosity
Slide 16 : Density of Water 11.3 Water is a Unique Substance
Slide 17 : A crystalline solid possesses rigid and long-range order. In a crystalline solid, atoms, molecules or ions occupy specific (predictable) positions. An amorphous solid does not possess a well-defined arrangement and long-range molecular order. A unit cell is the basic repeating structural unit of a crystalline solid. Unit Cell Unit cells in 3 dimensions 11.4 At lattice points:
Atoms
Molecules
Ions
Slide 18 : 11.4
Slide 19 : 11.4
Slide 20 : Types of Crystals Ionic Crystals – Ion-Ion interactions are the strongest (including the “intermolecular forces” (H bonding, etc.)
Lattice points occupied by cations and anions
Held together by electrostatic attraction
Hard, brittle, high melting point
Poor conductor of heat and electricity CsCl ZnS CaF2 11.6
Slide 21 : Types of Crystals Covalent Crystals – Stronger than IM forces but generally weaker than ion-ion
Lattice points occupied by atoms
Held together by covalent bonds
Hard, high melting point
Poor conductor of heat and electricity 11.6 diamond graphite
Slide 22 : Types of Crystals Molecular Crystals
Lattice points occupied by molecules
Held together by intermolecular forces
Soft, low melting point
Poor conductor of heat and electricity 11.6
Slide 23 : Types of Crystals Metallic Crystals – Typically weaker than covalent, but can be in the low end of covalent
Lattice points occupied by metal atoms
Held together by metallic bonds
Soft to hard, low to high melting point
Good conductors of heat and electricity 11.6 Cross Section of a Metallic Crystal
Slide 24 : An amorphous solid does not possess a well-defined arrangement and long-range molecular order. A glass is an optically transparent fusion product of inorganic materials that has cooled to a rigid state without crystallizing Crystalline
quartz (SiO2) Non-crystalline
quartz glass 11.7
Slide 25 : Types of Crystals 11.6
Slide 26 : Chemistry In Action: High-Temperature Superconductors
Slide 27 : Evaporation 11.8 Condensation
Slide 28 : The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation 11.8
Slide 29 : Molar heat of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid. P = (equilibrium) vapor pressure T = temperature (K) R = gas constant (8.314 J/K•mol) 11.8 C = constant (depends on P & T)
Slide 30 : The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure. The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm. 11.8
Slide 31 : The critical temperature (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. The critical pressure (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature. 11.8
Slide 32 : Melting 11.8 Freezing The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium
Slide 33 : Molar heat of fusion (DHfus) is the energy required to melt 1 mole of a solid substance. 11.8
Slide 34 : 11.8
Slide 35 : Sublimation 11.8 Deposition Molar heat of sublimation (DHsub) is the energy required to sublime 1 mole of a solid. DHsub = DHfus + DHvap ( Hess’s Law)
Slide 36 : A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas.
The triple point is where all 3 phases meet. Phase Diagram of Water 11.9
Slide 37 : 11.9
Where’s Waldo? : Where’s Waldo? Can you find…
The Triple Point?
Critical pressure?
Critical temperature?
Where fusion occurs?
Where vaporization occurs?
Melting point (at 1 atm)?
Boiling point(at 6 atm)? Carbon Dioxide
Slide 39 : 11.9
Slide 40 : Chemistry In Action: Liquid Crystals