Chapter 11: Liquids and Solids Intermolecular Forces The addition of heat changes the state of a compound from solid to liquid to gas as kinetic and potential energy are added to the molecules Kinetic Energy involves the motion of the molecules Potential Energy involves how far apart the molecules are Intermolecular Forces hold the molecules together Ion-Dipole Interactions: Na+Cl- interactions with water Dipole-Dipole Attractions: interaction of polar molecules Hydrogen Bonding: special dipole-dipole attraction in molecules where H is bonded to an electronegative atom (O, N, F, etc…) Small size of H lets the dipoles get very close Large electronegativity difference makes attraction great

Intermolecular Forces Ion-Dipole Forces Dipole-Dipole Forces H-Bonding

d. London Dispersion Forces: temporary dipole moments can form when electrons are unsymmetrically distributed. Even nonpolar molecules have this type of attraction.

3. Boiling point trends and Intermolecular Forces Boiling Point increases as Mass and Intermolecular Forces Increase i. Dipole moment decides B.P. if similar mass compounds ii. Longer alkanes have more surface area = more dispersion forces iii. H2O doesn’t follow the trend: H-bonding holds water together

The liquid state Liquids are required for life Water solutions are required for many biological reactions to occur Food preparation, cleaning, cooling, etc… require liquids Characteristics of liquids: non-compressible, takes shape of container, dense Surface Tension = resistance of a liquid to an increase in its surface area Surface molecules are not involved in all possible intermolecular bonding Requires energy to go the surface, so liquid resists increases in surface area The higher the intermolecular forces, the higher the surface tension

Capillary Action = spontaneous rising of a liquid up a narrow tube Adhesive Forces = polar liquid has intermolecular forces with polar surface Cohesive Forces = intermolecular forces of the liquid for itself Water: Adhesive (H-Bonding) > Cohesive, so concave meniscus Mercury: Cohesive (London) > Adhesive, so convex meniscus Viscosity = a liquid’s resistance to flow Large intermolecular forces would cause high viscosity (glycerol) Large, complex molecules can become physically entangled (grease) Structural Model for Liquids Gas: molecules so far apart, treat as if no intermolecular forces Solid: molecules strongly held together, treat as if no motion Liquid: strong forces plus motion of particles Ordered regions (but less so than solids) that are changing all the time

The Solid State Classification of Solid Structures Crystalline Solids = regular arrangement of components in 3 dimensions Amorphous Solids = disordered arrangement of components Will not be the focus of this chapter Glasses = “frozen solutions” are disordered, amorphous solids Crystal Structure Basics Crystal = a piece of a crystalline solid Lattice = 3-dimensional system of designating where components are Unit cell = smallest repeating unit of the lattice Examples: simple cubic, body-centered cubic, face-centered cubic

Three different cubic unit cells and lattices

X-Ray Analysis of Crystalline Solids Diffraction = scattering of light by a crystal’s regular array of components Wavelength of light must be about the same as the spacing of units Constructive interference occurs when different distances traveled by the same wavelength of light is an integer multiple of l Destructive interference occurs elsewhere

Diffractometer = computerized system to rotate crystal while shining X-rays at them and to record the diffraction data produced Diffraction pattern tells us about how far apart the components are Bragg Equation: nl = 2dsinq Lets us calculate the distance between crystal components Bragg’s awarded 1915 Nobel Prize for crystallography Example: find d if n = 1, l = 1.54 Å, q = 19.3o

4. Types of Crystalline Solids

Metal Structure and Bonding The type of crystalline structure helps us explain the properties of solids Argon (Group8A): mp = -189 oC, insulator for heat and electricity Diamond (Network Atomic): mp = 3500 oC, very hard, insulator Copper (Metallic Atomic): mp = 1083 oC, conductor, malleable, ductile Metal Structure and Bonding Properties (see Copper above) result from non-directional covalent bonds Malleable and High mp: indicates strong, non-directional bonds Difficult to separate Easy to move positions, as long as they stay in contact Electron Sea Model = valence electrons don’t belong to any specific atom Array of metal cations surrounded by a sea of valence electrons This would also account for electrical and heat conductance Band (or MO) Model = Large MO’s form from billions of AO’s When two atoms bind, we can form two widely spaced MO’s When many atoms bind, we form a closely spaced band of MO’s Core electrons still localized, only valence electrons in the “sea” Empty MO’s available to electrons: heat/electricity conductance

Electron Sea Model Band or MO Model