1 Ch 11 Intermolecular Attractions and The Properties of Liquids and Solids Brady & Senese, 5th Ed.

1

Ch 11 Intermolecular Attractions and The Properties of Liquids and Solids

Brady & Senese, 5th Ed.

2

Index

11.1. Gases, liquids, and solids differ because intermolecular forces depend on the distances between molecules11.2. Intermolecular attractions involve electrical charges11.3. Intermolecular forces and tightness of packing affect the physical properties of liquids and solids11.4. Changes of state lead to dynamic equilibria11.5. Vapor pressures of liquids and solids are controlled by temperature and intermolecular attractions11.6. Boiling occurs when a liquid's vapor pressure equals atmospheric pressure11.7. Energy changes occur during changes of state11.8. Changes in a dynamic equilibrium can be analyzed using Le Châtelier's principle11.9 Crystalline solids have an ordered internal structure11.10 X-Ray diffraction is used to study crystal structures11.11 Physical properties of solids are related to their crystal types11.12. Phase diagrams graphically represent pressure-temperature relationships

11.1. Gases, liquids, and solids differ because intermolecular forces depend on the distances between molecules

3

States Of Matter

• Condensed phases have greater interaction between particles

• Conversion to less condensed phases requires energy

11.2. Intermolecular attractions involve electrical charges 4

Electronegativity Review

Electronegativity: A measure of the attractive force that one atom in a covalent bond has for the electrons of the bond


Bond Dipoles

• Two atoms with different electronegativity values will share electrons unequally

• Electron density is uneven, with a higher charge concentration around the more electronegative atom

• Bond dipoles are indicated with delta (δ) notation that indicates that a partial charge has arisen


Net Dipoles

• Symmetrical molecules, even if they have polar bonds, are non-polar because the bond dipoles cancel

• Asymmetrical molecules are polar because the bond dipoles do not cancel-- they have permanent, net dipoles

• Molecular dipoles cause molecules to interact, and the distance between the molecules increases the amount of interaction


Dipole - Dipole Attractions

Interaction between the net dipoles in polar molecules are called dipole-dipole attractions. About 1% as strong as a covalent bond Decrease as molecular distance increases


Dipole-Dipole Interactions (H-bonding)

• Especially strong attractions found in polar molecules with hydrogen atoms bonded to F,O, or N

• These strong dipole-dipole interactions are called hydrogen bonds


Case Study: Snowflakes

What accounts for the fact the that snowflakes are always 6-sided?

10

Your Turn!

Which of the following is not likely to have hydrogen bonding? Hint- sketch the molecules!

A. CH3CO2H

B. CH3OH

C. CH3O2CH3

D. All of these exhibit hydrogen bonding

11

Your Turn!

Which statements are true of a molecule that exhibits dipole-dipole attractions?

i. It is polar

ii. It is asymmetrical

iii. It must contain H attached to F, O, or N

A. i & ii only

B. ii & iii only

C. i only

D. ii only

E. iii only


London Forces

• When atoms near one another, their valence electrons interact

• Repulsion causes the electron clouds in each to distort and polarize

• Instantaneous, induced dipoles result from this distortion


London Forces (con.)

• effect enhanced with increased particle mass

• effect diminished by increased distance between particles


Shape & Attraction

• Longer atom chains exert greater the attraction.• Compact molecules have fewer sites for interaction• Compact molecules have lower attraction for one

another


Intermolecular Attractions

ionic

charged particles attract one another

polar covalent

dipoles attract one another

non-polar covalent

electrons synchronize

contain H-X bonds

X= F, O, or N

do not contain H-X bonds

X= F, O, or N

ionic attractions

and London forces

hydrogen bonding

and London forces

dipole-dipole attractions

and London forces

London forces


Compounds of Different Polarity Interact

• Ionic compounds interact with polar molecules using ion-dipole forces

• Ionic compounds can induce dipoles in non-polar molecules, resulting in ion-induced dipoles

17

Your Turn!

Which of the following is not a true statement

A. All molecules exert London Forces

B. Only non-polar molecules exert London Forces

C. The greater the mass the greater the London Force

D. Another name for London Forces in “induced dipole attraction”


Effects of Intermolecular Forces (IMF)

Attractive

Force

MP/ BP/ density/ surface tension/ viscosity

Vapor Pressure/ Rate of Evaporation

Increasing IMF Increasing Decreasing

Increasing molar mass

Increasing Decreasing

Increasing branching

Increasing Decreasing


Learning Check

Identify the kinds of intermolecular forces present in the following compounds and then rank them in order of increasing boiling point: H2S, CH3OH, CBr4, and Ne

C Br

Br

Br

Br

HS

HC O

H

HH

HNe

hydrogenbonding

London forces

London forces

dipole-dipole

MM=331.63 MM=20.18•CH3OH >H2S> CBr4> Ne

20

Your Turn!

Arrange the following in terms of increasing strength of intermolecular forces: CH4, CO2, HF

A. CH4>CO2>HF

B. CO2>HF>CH4

C. HF>CH4>CO2

D. None of theseHF>CO2>CH4

11.3. Intermolecular forces and tightness of packing affect the physical properties of liquids and solids

21

Packing Effects

• Gases have high compressibility due to the spaces between particles

• Diffusion is impeded by collisions, hence improved in gases


22

Surface Tension

surface tension - resistance to spreading out and increasing surface area


23

Viscosity

• Viscosity - resistance to flow

• larger molecules collide and interact more often, impeding their flow


24

Wetting

• Wetting - the ability of a liquid to spread across a surface

• The greater the similarity in attractive forces between the liquid and the surface, the greater the wetting effect


25

Solubility

• “Like dissolve like”- the more similar the polarity of two substances, the greater their ability to interact with each other rather

• Surfactants substances that have polar and non-polar

characteristics improve a liquid’s wetting properties allow non-polar substances to dissolve in polar

solvents

26

Your Turn!

Which of the following are not expected to be soluble in water?

A. HF

B. CH4

C. CH3OH

D. All are soluble


27

Changes of state involve IMF

Gas State

Liquid State

Solid State

sublimation

evaporation

meltingfusion

condensation

deposition

Overcoming or establishing intermolecular attractions results in a change in energy

Exothermic, releases heat Endothermic, absorbs heat


28

Rates Of Evaporation Vary With Temperature

11.4. Changes of state lead to dynamic equilibria 29

Changes Of State Involve Equilibria

• The fraction of molecules in the condensed state is higher when the intermolecular attractions are higher

• Intermolecular attractions must be overcome to separate the particles, while the separated particles are simultaneously attracted to one another

separated phasecondensed phase


Boiling Involves Equilibrium


Melting Involves Equilibrium• As solid melts, particles separate and liquid forms• liquid particles simultaneously interact to reform solid• At equilibrium, the rates of both processes are equal• A similar equilibrium exists when liquid vaporizes and gas simultaneously

condenses

11.5. Vapor pressures of liquids and solids are controlled by temperature and intermolecular attractions

32

Vapor Pressure

• vapor pressure-the pressure of a gas in a closed container in which the solid and liquid phases are at equilibrium

• liquid + heat of vaporization ↔ gas

• Varies with the temperature and substance

11.6. Boiling occurs when a liquid's vapor pressure equals atmospheric pressure 33

Boiling Point

• The temperature at which vapor pressure equals the atmospheric pressure, is called the boiling point

• Normal boiling point specifies that the atmospheric pressure achieved is 1 atm


Case Study: The “Love Meter”

A liquid is trapped in a closed container. When the bottom bulb is held in the hand, the liquid rises up the tube into the upper bulb and appears to boil.

• Is the liquid boiling?

• What causes the change?


Case Study : Love On The Rocks

When the love meter is placed onto a table and a cube of ice is applied to the top bulb, the liquid appears to boil as before.

• Is this boiling?

• Why does this happen?


Intermolecular Attractions Affect Boiling Point

37

Your Turn!

Which of the following will affect the boiling point of a substance?

A. Molecular mass of the material

B. Intermolecular attractions

C. The external pressure on the material

D. All of these

E. None of these

11.7. Energy changes occur during changes of state 38

Heating Curve


Cooling Curve


Changes Of State Involve Energy

Gas State

Liquid State

Solid State

Enthalpy of sublimationEnthalpy

of fusion

Enthalpy of Vaporization

• Phase changes involve specific energies• Energy is released when a more condensed phase

is formed

(-)Exothermic, releases heat (+)Endothermic, absorbs heat

11.8. Changes in a dynamic equilibrium can be analyzed using Le Châtelier's principle 41

LeChâtelier’s Principle

• Any change to the quantities or conditions may cause the system to “shift” to re-establish equilibrium

• Increasing heat causes all endothermic processes to shift to form more product

• Increases in pressure results in a shift toward the more condensed phase

11.9 Crystalline solids have an ordered internal structure 42

Crystal Structures Have Regular Patterns

• The smallest segment that repeats regularly is a unit cell• The unit cell repeats to form a regular highly symmetrical lattice• Square lattices have symmetry in 2 dimensions• Cubic lattices have symmetry is 3 dimensions


Three Types Of Unit Cells

• Crystals take common unit cell shapes: Simple cubic Body-centered cubic (BCC) Face- centered cubic (FCC)

• Type of unit cell depends on size of atoms involved


Simple Cubic

• Has one host atom at each corner edge length (a) = 2r where r is the radius of the atom or ion.


Body-centered Cubic (BCC)

• has one atom at each corner and one in the center edge length

3

4ra


Face- centered Cubic (FCC)

has one atom centered in each face, and one at each corner

ra 22


Spaces In Ionic Solids Are Filled With Counter Ions• In NaCl, the Cl- ions form a

unit cell that is face centered cubic

• Na+ ions, being smaller, fill the spaces between the Cl- ions

• If we count the atoms in the unit cell we have 6 of each, thus a 1:1 Na+:Cl- ratio


Learning Check: Identify the Formula for Each, Based on the Unit Cell.

CaF2CsF ZnS


Your Turn!

Which formula would be consistent with the face centered cubic unit cell shown?

A. GB4

B. GB

C. G4B16

D. None of these


Some Factors affecting crystalline structure

• the size of the atoms or ions involved• the stoichiometry of the salt.• the materials involved (some substances do not

form crystalline solids)


Unit Cells Stack To Form Crystal Lattice

• Square lattice- 2-dimensional arrays• Close packed structures: atoms are layered so

that the holes in one layer are covered by the atoms in the next layer cubic closest packed -3 alternating layers hexagonal close packed-2 alternating layers


Amorphous Solids (Glass)

• Have little order, thus referred to as “super cooled liquids”

• Edges are not clean, but ragged due to the lack of order


Your Turn!

Which factor does not affect the type of crystal

A. the radius of the ions

B. the ratio of the numbers of anions : cations

C. the molar mass of the ions

D. all affect the crystal

11.10 X-ray diffraction is used to study crystal structures 54

X-Ray Crystallography

• X-rays are passed through a crystalline solid.

• Some x-rays are absorbed, most re-emitted in all directions

• Some emissions by the atoms are in phase, others out of phase

• Emission is recorded on film.


X-ray Diffraction


Interpreting Diffraction Data

• helps us estimate atomic and ionic radii

• nλ=2dsinθ n = an integer (1, 2, …) = wavelength of the

X–rays d = the interplane

spacing in the crystal = the angle of

incidence =the angle of reflectance of X–rays to the crystal planes


Learning Check: Diffraction Data

The diffraction pattern of copper metal was measured with x-ray radiation of wavelength of 1.315Å. The first order (n=1) Bragg diffraction peak was found at an angle theta of 50.5 degrees. Calculate the spacing between the diffracting planes in the copper metal.

1(1.315 Ǻ)=2×d×sin(50.5°)nλ=2dsinθ

2.83 Ǻ =d


Learning Check

Silver packs together in a faced center cubic fashion. The interplanar distance, d, corresponds to the length of a side of the unit cell, and is 4.07 angstroms. What is the radius of a silver atom?

ra 22r22A07.4

r = 0.536 angstroms

11.11 Physical properties of solids are related to their crystal types 59

Ionic Crystals (ex. NaCl, NaNO3)

• Cations and anions found at lattice sites

• Relatively hard and brittle

• high melting points• Have strong attractive

forces between ions • Do not conduct

electricity in their solid states

• Conduct electricity well when molten


Molecular Crystals (ex. H2O, CO2)

• Lattice sites occupied either by atoms or by molecules

• If the molecules are relatively small, the crystals tend to: be soft have low melting points be held together by relatively weak intermolecular

attractions


Covalent Crystals

• Lattice positions occupied by atoms that are covalently bonded to other atoms at neighboring lattice sites

• Called network solids - interlocking network of covalent bonds extending all directions

• Covalent crystals tend to: be very hard have very high melting points have strong attractions between covalently bonded

atoms. • Examples: are quartz (SiO2) , silicon carbide (SiC)

and diamond

13.3. Physical properties of solids are related to their crystal types 62

Metallic Crystals• Simplest models: lattice positions of a

metallic crystal occupied by positive ions

• Conduct heat and electricity well “cloud” of valence electrons surrounds

ions moving electrons transmit kinetic energy

rapidly through the solid

• lustrous When light shines on the metal, loosely

held electrons vibrate easily and re-emit the light with essentially the same frequency and intensity


Learning Check: Classify the following in terms of likely structure

ionic molecular covalent metallic

Sulfur, a substance that pulverizes when struck, is non-conductive of heat and electricity

Substance X. A white crystalline solid that conducts electrical current when molten or dissolved.

Z: shiny, conductive malleable with a high melting temperature.


Your Turn!

molecular crystals can contain all of the listed attraction forces except:

A. dipole-dipole attractions

B. electrostatic forces

C. London forces

D. hydrogen bonding

11.12. Phase diagrams graphically represent pressure-temperature relationships 65

Phase Diagrams

• Show the effects of both pressure and temperature on phase changes

• Boundaries between phases indicate equilibrium.• Triple point: the temperature and pressure at

which s,l, and g are all at equilibrium• Critical point: the temperature and pressure at

which a gas can no longer be condensed


Phase Diagram of Water


Case Study: An Ice Necklace

• A cube of ice may be suspended on a string simply by pressing the string into the ice cube. As the string is pressed onto the surface, it becomes embedded into the ice.

• Why does this happen?


Phase Diagram – CO2


Your Turn!

At 89 °C and 760 mmHg, what physical state is present?

A. Solid

B. Liquid

C. Gas

D. Supercritical fluid

E. Not enough information is given

Date post:	02-Jan-2016
Category:	Documents
Upload:	shon-oconnor
View:	221 times
Download:	2 times

1 Ch 11 Intermolecular Attractions and The Properties of Liquids and Solids Brady & Senese, 5th Ed.

Documents