AP ChemistryChapter 10 NotesRemember from Chemistry Class:Intramolecular forces: ionic, metallic, covalent bonds (chapters 8 and 9)

much stronger than IM forcesIntermolecular (IM) forces: (see flow chart)

when substances change state, molecules remain intact, these forces are broken

Label each picture according to the type of IM force it illustrates:

According to the KMT, what three assumptions can we make?1. particles in constant, rapid, random motion (neglect intermolecular forces)2. particles have no volume, exist as “point masses”3. collisions are perfectly elastic (energy is perfectly conserved)

gases: weakest IM forces, particles move independently of one anotherliquids: stronger IM forces but allowed to flow

(gases and liquids are fluids, the particles slip easily by one another)solids: strongest IM forces, particles vibrate around fixed points

Why do noble gases have such low melting points?LIQUIDS:Some properties of liquids compared to gases:

low compressability

Are polar molecules involved?

Are H atoms bonded to N, O or F?

Hydrogen bonding

examples: H2O, NH3, HF

dipole-dipole forces

examples: H2S, CH3Cl

London dispersion forces onlyexamples:

Ar, I2

lack of rigidity high density

IM forces will cause them to bead as droplets (surface tension)(a sphere has maximum volume for minimum surface area)

Polar liquids will exhibit capillary action: spontaneous rising of a liquid in a narrow tube.

cohesive forces (IM forces among molecules) adhesive forces (IM forces between liquid molecules and their container - glass)

water (polar molecule) has a CONCAVE meniscus because the adhesive forces are stronger than the cohesive forces

non-polar molecules will have a CONVEX meniscus in a graduated cylinder

viscosity: resistance to flow

glycerol has a high viscosity because of the high capacity to form H bonds

Viscosity also increases as molecular complexity increases because the molecules become “entangled” with themselves and one another. Example:

Gasoline: non-viscous Formula: CH3 – (CH2)n – CH3 where n is from 3-8

Grease: very viscousFormula: CH3 – (CH2)n – CH3 where n is from 20-25

SOLIDS:Two types:

1. Amorphous solids: disordered structureExample:

Glass – the components are “frozen” in place before it can achieve an ordered arrangement

2. Crystalline solids: regular arrangement (in a crystal)

lattice: 3D system of points designating position of components (atoms, ions or molecules) that make up the substanceunit cell: smallest repeating unit of a lattice3 common crystals:

Simple cubic (SC) 1 atom per unit cell Body centered cubic (BCC) 4 atoms per unit cell Face centered cubic (FCC) 8 atoms per unit cell

The extended structures shown below are a series of repeating unit cells that share common forces in the interior of a solid.

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Simple cubic

Body-centered cubic

Face-centered cubic

(c)

(b)

(a)

Unit cell Lattice Example

Poloniummetal

Uraniummetal

Goldmetal

Simple Cubic: 1 atom per unit cell side length (d0 = 2r)

Body Centered Cubic: 2 atoms per cell body diagonal = d0 √3 = 4r do √2 = diagonal through the base of cube.

Face Centered Cubic: 4 atoms per cell Face diagonal = d0 √2 = 4r d0√2 = diagonal through face of the cube

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(a) (b) (c)

12

atom

18

atom

Using Bragg’s equation:

X-ray diffraction: beams of light scattered from a regular array of points in which the spacings between components are comparable with the wavelength of light.

Constructive interference – in phaseDestructive interference – out of phaseLabel the following waves as constructive or destructive

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Waves inphase beforestriking atoms

Waves reinforceeach other, since(d2 - d1) is anintegral number ofX- ray wavelengths.

Waves stillin phase

Waves inphase beforestriking atoms

Waves cancel,because in this case(d2 - d1) is one halfX- ray wavelengths.

No resultantwave

Bragg’s equation: Used for analysis of crystal structures and to calculate the distance between planes in crystals.The distance traveled by the x-rays is an integral number of wavelengths

nλ = 2d sin θ

d = distance between atomsn = an integer

λ= wavelength of the x-raysθ = angle of reflection

Can you think of a practical application of Bragg’s equation?

Example problem: (make sure your calculator is in degrees!)X rays of wavelength 1.54 Å were used to analyze an aluminum crystal. A reflection was produced at θ = 19.3 degrees. Assuming n = 1, calculate the distance, d, between the planes of atoms producing this reflection.

3 types of Crystalline Solids: classified according to what type of component occupies the lattice points. (see table bleow)

Classification of Solids:Atomic Solids Molecular

SolidsIonic

SolidsMetallic Network Group 13Component

s that occupy lattice points

metal atoms non-metal atoms

group 13atoms

discrete molecules

ions

Bonding delocalized covalent

directional covalent

(molecules)

London Dispersion

forces

Dipole-Dipole and/orL. D. F.

Ionic

Properties range of hardness and

melting points,

conductor

hard, high melting point,

insulator

very low melting poins

low melting points,

insulator

high melting points

Examples silver, iron, brass

diamond solid argon is another example

ice, dry ice NaCl, CaF2

What is the difference between ionic solids and molecular solids?10_216

= Cl

= Na

Sodium chloride

(b)

= H2O= CDiamond Ice

(a) (c)

Packing in Metals:Model: Packing uniform, hard spheres to best use available space. This is called closest packing. Each atom has 12 nearest neighbors. (pictures on next pages)

- hexagonal closest packed (“aba”)- cubic closest packed (“abc”)

1. Closest packing arrangement of uniform spheres -- aba. This forms hexagonal closest packed -- hcp.

2. Atoms arranged in aba pattern forming hexagonal closest packed (hcp) structure -- 2 atoms/cell.

Label the diagrams to the left as:

Ionic solidAtomic solidMolecular solid

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View from above

View from side(b)(a) (c)

Hexagonal closest packed structure – central atom has 12 nearest neighbors.

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b

a

b

hcp

1 23

46

5

789

111210

Face-centered cubic is cubic closest packed (ccp). The spheres are packed in an abc arrangement.

Calculate density of a closest packed solid

Silver crystallizes in a cubic closest packed structure. The radius of a silver atom is 144 pm. Calculate the density of solid silver.

Bonding Models for Metals:Electron Sea Model: A regular array of metals in a “sea” of electrons.

Band (Molecular Orbital) Model: Electrons assumed to travel around metal crystal in MOs formed from valence atomic orbitals of metal atoms.

Conduction Bands: closely spaced empty molecular orbitals allow conductivity of heat and electricity.

Representation of the energy levels (bands) in a magnesium crystal. 1s, 2s, & 2p orbitals are localized, but 3s & 3p orbitals are delocalized to make molecular orbitals.

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12+ 12+ 12+ 12+ 12+

Empty MOs

Filled MOs

Ene

rgy

3p

3s

Magnesiumatoms

2p

2s

1s

Metal Alloys:Substances that have a mixture of elements and metallic properties.

1. Substitutional Alloy: some metal atoms replaced by others of similar size. (brass = Cu/Zn)

2. Interstitial Alloy: Interstices (holes) in closest packed metal structure are occupied by small atoms.(steel = iron + carbon)

3. Both types: Alloy steels contain a mix of substitutional (Cr, Mo) and interstitial (Carbon) alloys

Network Solids: Composed of strong directional covalent bonds that are best viewed as a “giant molecule”

- brittle- do not conduct heat or electricity- carbon, silicon-based

Examples: graphite, diamond, ceramics, glass10_229

Diamond(a)

Semiconductors: A substance in which some electrons can cross the band gap- Conductivity is enhanced by doping with group 3a or group 5a elements. (13, 15)- n-type semiconductor -- doped with atoms having more valence electrons --

Phosphorus.- p-type semiconductor -- doped with atoms having fewer valence electrons -- Boron.- See Figure 10.31 on page 478 in Zumdahl.

Molecular Solids:

• molecular units at each lattice position.• strong covalent bonding within molecules.• relatively weak forces between molecules.• London Dispersion Forces -- CO2, I2, P4, & S8.• Hydrogen Bonding -- H2O, NH3, & HF.

Trigonal, Tetrahedral and Octahedral Holes:1. Trigonal holes -- formed by three spheres in the same layer.2. Tetrahedral holes -- formed when a sphere sits in the dimple of three spheres in an

adjacent layer.3. Octahedral holes -- formed between two sets of spheres in adjoining layers of closest

packed structures.

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Trigonalhole

Tetrahedralhole

Octahedralhole

(a)

(b)

(c)

Heagonal or Cubic closest packed:- octahedral hole for each atom or ion.- 2 tetrahedral holes for each atom or ion.- simple cubic and body-centered cubic are not closest packed structures!

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(a) (b) (c)ZnS

(Above)The location (x) of a tetrahedral hole in the face-entered cubic unit cell. The S2- ions are closest packed with the Zn2+ ions in alternating tetrahedral holes.

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(a)

(b)

(Above)The location (x) of an octahedral hole in the face-centered cubic unit cell. The Cl- ions have a ccp arrangement with the Na+ ions in all the octahedral holes.

Vapor Pressure:is the pressure of the vapor present at equilibrium.. . . is determined principally by the size of the intermolecular forces in the liquid.. . . increases significantly with temperature.

Volatile liquids have high vapor pressures.

Low boiling point • _____ vapor pressure. • _____ intermolecular forces.

Low vapor pressure• _____ molar masses.• _____ intermolecular forces.

Boltzman Distribution (below)-- number of molecules in a liquid with a given energy versus kinetic energy at two different temperatures.

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T1

Kinetic energy(a)

Num

ber o

f mol

ecul

esw

ith a

giv

en e

nerg

y Energy neededto overcomeintermolecular forces in liquid

T2

Kinetic energy(b)

Num

ber o

f mol

ecul

esw

ith a

giv

en e

nerg

y Energy neededto overcomeintermolecular forces in liquid

Natural Log of Vapor Pressure Versus Reciprocal Kelvin Temperature:y = mx + b

Slope = If the slope is known, then H can be calculated.

Clausius-Clayperon Equation:

Temperatures must be expressed in Kelvin.

Example 10.6 on page 487 in Zumdahl.The vapor pressure of water at 25 ˚C is 23.8 torr, and the heat of vaporization of water at 25 ˚C is 43.9 kJ/mol. Calculate the vapor pressure of water at 50.˚C(use Clausius-Clayperon Equation to solve)

Sublimation:• Change of a solid directly to a vapor without passing through the liquid state. • Iodine• Dry Ice• Moth Balls

Melting Point: Molecules break loose from lattice points and solid changes to liquid. (Temperature is constant as melting occurs.)

vapor pressure of solid = vapor pressure of liquid

Boiling Point: Constant temperature when added energy is used to vaporize the liquid.

vapor pressure of liquid = pressure of surrounding atmosphere

Heating curve for water. H = (m Ts)ice + m Hf + (m Ts) water + m Hv + (m Ts)steam

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Tem

pera

ture

(°C

)

Time

– 20

0

20

40

60

80

100

120

140Steam

Water and steam

Water

Ice andwater

Ice

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Water vapor

Solidwater

Liquidwater

Solid and liquid water interact only through the vapor state.Phase Diagram:Represents phases as a function of temperature and pressure. critical temperature: temperature above which the vapor cannot be liquefied.

critical pressure: pressure required to liquefy AT the critical temperature.

critical point: critical temperature and pressure (for water, Tc = 374°C and 218 atm).

Phase diagram for water -- Tm is the regular melting point. The solid/liquid line has a negative slope.

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Pc = 218

1.00P3 = 0.0060

Tm T3 Tb

0 0.0098 100 374

Solid Liquid

Gas

Temperature ( ° C)

Pre

ssur

e (a

tm)

Triplepoint

Criticalpoint

Tc

Phase diagram for carbon dioxide -- the solid/liquid line has a positive slope.10_255

Pc =72.8

1.00

P3 =5.1

Tm T3 Tc

Solid

Liquid

GasTriplepoint

Temperature (°C)

– 78 – 56.6 31

Pre

ssur

e (a

tm)

Criticalpoint

Note the different scales why does carbon dioxide sublimate at STP?Phase diagram for sulfur -- note the two different solid forms of rhombic and monoclinic sulfur.

10_256

Pre

ssur

e (m

m H

g)

Temperature (°C)

Rhombic

Liquid

Mon

oclin

ic

(119°C, 0.0027 mm Hg)

(96°C, 0.0043 mmHg)

Vapor

Phase diagram for carbon -- note the two solid forms of diamond and graphite.

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Diamond

Graphite

Liquid

Vapor

107

109

1011

0 2000 4000 6000Temperature (K)

Pre

ssur

e (P

a)