CH. 10 Solids & Liquids

What are dispersion forces?

Fleeting, temporary dipoles resulting in weak electrostatic forces between molecules when very close together

What is polarizability?

Measure of how easy or difficult it is for another electrostatic charge to distort a molecule’s charge distribution

Hydrogen bonding

Unusually strong type of dipole dipole attraction

Strongest IMF, present only in certain polar molecules with N—H, O—H, or F—H bonds

Dipole-dipole attractions

-Molecules with permanent dipoles

-Present only in polar molecules

-Stronger with higher dipole moments

-Usually stronger than dispersion forces

-Molecules arrange to align opposite charges

-NOT included in van der waals forces are attractive forces between polar molecules due to their permanent dipoles, leading to interactions that orient the molecules to maximize attraction. W

Cohesive forces

Attractions between IDENTICAL molecules of a substance

Adhesive forces

Attractions between DIFFERENT types of molecules

Viscosity

The measure of a liquid’s resistance to flow

Surface tension

The energy required to increase the area, or length of a liquid surface by a certain amount

-Water droplets minimize SA for lowest enegy

-Water surfaces behave like a stretched rubber membrane

-Cohesive forces are due to hydrogen bonding

Capillary action

Liquid flow within a porous material due to attraction of the liquid to the surface of the material and to other liquid molecules

What does the height of the liquid in a capillary tube depend on?

-The liquid’s density, surface tension, and contact angle with the tube

-The radius of the tube and the acceleration of gravity

Vapor Pressure (equilibrium)

The pressure exerted by a vapor in equilibirium with a liquid in a closed container at a given temperature

Normal boiling point of a liquid

The temperature at which the liqudi boils when the presure above the liquid is 1 atm

Enthalpy of Vaporization

The energy required to vaporize one mole of a liquid substance at a temperature, it is always endothermic

Enthalpy of Fusion

The energy required to melt one mole of a solid substance at a temperature, it is always endothermic

Enthalpy of Sublimation

The energy required to convert one mole of a solid substance directly to the gaseous state and is always endothermic

Phase diagram

A map for the phases of matter at given temperatures and pressures

It combines P vs. T plots for solid-liquid, liquid-gas, and solid-gas phase transition equilibria for a substance

Triple point (Point B)

The temperature and pressure at which solid, liquid, and vapor of a substance are all in equilibirium

Critical point (Point C)

the temperature and pressure above which a gas cannot be condensed into a liquid

Supercritical fluid

High density, low viscosity phase intermediate between liquid and gas

Crystalline solids

Solids in which atoms, ions, or molecules are arranged in a definite repeating pattern

Amorphous solids

Glassy/noncrystalline solids that lack and ordered internal structure

Ionic solid

Solid composed of cations and anions held together by strong electrostatic attractions

Metallic solid

Solid composed of metal atoms held together by metallic bonding of atomic nuclei in a delocalized “sea of electrons”

-Lustrous, malleable, highly conductive (thermal + electrical)

-Many hard structures with widely varying melting points

Covalent Network solid

Solid whose particles are held together by covalent bonds

-Common for minerals

-High melting, hard, strong, not conductive

-Graphite is exception due to sheets

Molecular solid

Solid composed of neutral molecules held together by intermolecular forces of attraction

-Strength of IMFs varies greatly

Small nonpolar molecules = weak attractions, low melting points

Large nonpolar molecules = higher attractions, higher melting points

Polar moelcules - highest melting points

Defects of crystalline solids

-Similarly sized atoms and ions can substitute

-Atoms can be missing (vacancies)

-Smaller sized atoms and ions can fill interstitial sites between atoms and ions

Unit cell

The simplest repeating unit in a crystalline solid

-The lattice points represent the center of atoms or ions

Simple cubic (sc) unit cell

Contains an atom at each of the corners of the unit cell cube; there is a total of one atom within the unit cell

-Only Alpha Polonium has this structure

-Each corner contributes 1/8th of an atom to the unit cell

-Its corner atoms contact each other

Simple cubic unit cell formula

V = l³ = (2r)³

sc coordination number

6

Body-centered cubic unit cell (bcc)

Contains an atom at each of the corners of the unit cell cube and one interior atom at the center of the cube, there is a total of one atom within the unit cell

-The addition of a body-centered interior atom prevents corner atom contact

-The body centered interior atom contacts each corner atom

l=4/√3r with V = (4/√3r)³

bcc coordination number

8

fcc coordination number

12

Face-centered cubic unit cell (fcc)

Contains an atom at each of the corners of the unit cell cube and one atom at the center of each face; there are a total of 4 atoms within the unit cell. Noble gases have these structures

-Face centered atoms prevent contact

l = 2√2r with V = (2√2r)³)

Interior atoms

Completely contained in one unit cell and contribute 1 atom to that cell count

Face atoms

Shared between 2 unit cells and contribute ½ of an atom to each cell count

Edge atoms

Shared among 4 unit cells, contribute 1/4th of an atom to each cell count

Corner atoms

shared among 8 unit cells, contribute 1/8th of an atom to each cell count

Two ways to stack hexagonal layers for maximum density in three dimensions

1. Hexagonal close packed

2. Cubic Close packed

What is the highest density possible in two dimensions?

Hexagonal layer of atoms

Solid characteristics

-Particles are tightly packed, often in a regular pattern

-Particles vibrate about fixed positions

Liquid characteristics

-Particles are close together but no regular arrangement

-particles are mobile but in constant contact

Gas characteristics

-Particles far apart with no regular arrangement

-Particles move independently except when they collide

Intermolecular forces

Electrostatic forces between molecules that depend on the magnitude of δ+ and δ-

Instantaneous dipoles

Result from constant motion of electrons in moelcules and atoms

Induced dipoles

Result when an instantaneous dipole in one molecule or atom distorts the electrons in a neighboring atom or molecules

Higher viscosity results from stronger cohesive forces

-Molecules with stronger IMF

-Longer more complex molecular structures tangle

-Lower temperature liquids with lower kinetic energy molecules that are less able to overcome IMF

Vaporization and condensation

Liquid ⇌ vapor (gas)

Melting and freezing

Solid ⇌ liquid

Sublimation and deposition

Solid ⇌ gas