A. Intermolecular Forces1. 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 moleculesa. Kinetic Energy involves the motion of the moleculesb. Potential Energy involves how far apart the molecules are

2. Intermolecular Forces hold the molecules togethera. Ion-Dipole Interactions: Na+Cl- interactions with waterb. Dipole-Dipole Attractions: interaction of polar moleculesc. Hydrogen Bonding: special dipole-dipole attraction in molecules

where H is bonded to an electronegative atom (O, N, F, etc…)i. Small size of H lets the dipoles get very closeii. Large electronegativity difference makes attraction great

Chapter 11: Liquids and Solids

Dipole-Dipole Forces H-Bonding

Intermolecular Forces Ion-Dipole Forces

C O

H3C

H3C

C O

H3C

H3CH F H F H F

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

He He He

3. Boiling point trends and Intermolecular Forces

a. 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

B. The liquid state1. Liquids are required for life

a. Water solutions are required for many biological reactions to occur

b. Food preparation, cleaning, cooling, etc… require liquids

2. Characteristics of liquids: non-compressible, takes shape of container, dense

3. Surface Tension = resistance of a liquid to an increase in its surface area

a. Surface molecules are not involved in all possible intermolecular bonding

b. Requires energy to go the surface, so liquid resists increases in surface area

c. The higher the intermolecular forces, the higher the surface tension

4. Capillary Action = spontaneous rising of a liquid up a narrow tube

a. Adhesive Forces = polar liquid has intermolecular forces with polar surface

b. Cohesive Forces = intermolecular forces of the liquid for itself

c. Water: Adhesive (H-Bonding) > Cohesive, so concave meniscus

d. Mercury: Cohesive (London) > Adhesive, so convex meniscus

5. Viscosity = a liquid’s resistance to flow

a. Large intermolecular forces would cause high viscosity (glycerol)

b. Large, complex molecules can become physically entangled (grease)

6. Structural Model for Liquids

a. Gas: molecules so far apart, treat as if no intermolecular forces

b. Solid: molecules strongly held together, treat as if no motion

c. Liquid: strong forces plus motion of particles

Ordered regions (but less so than solids) that are changing all the time

C

C

H

OH C

OH

H O

H

H

H

H

Glycerol Grease

C. The Solid State1. Classification of Solid Structures

a. Crystalline Solids = regular arrangement of components in 3 dimensions

b. Amorphous Solids = disordered arrangement of components

a. Will not be the focus of this chapter

b. Glasses = “frozen solutions” are disordered, amorphous solids

2. Crystal Structure Basics

a. Crystal = a piece of a crystalline solid

b. Lattice = 3-dimensional system of designating where components are

c. Unit cell = smallest repeating unit of the lattice

d. Examples: simple cubic, body-centered cubic, face-centered cubic

Three different cubic unit cells and lattices

3. X-Ray Analysis of Crystalline Solids

a. Diffraction = scattering of light by a crystal’s regular array of components

i. Wavelength of light must be about the same as the spacing of units

ii. Constructive interference occurs when different distances traveled by the same wavelength of light is an integer multiple of

iii. Destructive interference occurs elsewhere

b. Diffractometer = computerized system to rotate crystal while shining X-rays at them and to record the diffraction data produced

c. Diffraction pattern tells us about how far apart the components are

d. Bragg Equation: n = 2dsin

i. Lets us calculate the distance between crystal components

ii. Bragg’s awarded 1915 Nobel Prize for crystallography

iii. Example: find d if n = 1, = 1.54 Å, = 19.3o

4. Types of Crystalline Solids

5. The type of crystalline structure helps us explain the properties of solids

a. Argon (Group8A): mp = -189 oC, insulator for heat and electricity

b. Diamond (Network Atomic): mp = 3500 oC, very hard, insulator

c. Copper (Metallic Atomic): mp = 1083 oC, conductor, malleable, ductile

D. Metal Structure and Bonding1. Properties (see Copper above) result from non-directional covalent bonds

a. Malleable and High mp: indicates strong, non-directional bonds

i. Difficult to separate

ii. Easy to move positions, as long as they stay in contact

b. Electron Sea Model = valence electrons don’t belong to any specific atom

i. Array of metal cations surrounded by a sea of valence electrons

ii. This would also account for electrical and heat conductance

c. Band (or MO) Model = Large MO’s form from billions of AO’s

i. When two atoms bind, we can form two widely spaced MO’s

ii. 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 SeaModel

Band or MO Model