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10/13/2016
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Unit 5 (Chp 11,13)
Bonds & IMAFs in
Liquids, Solids, and
SolutionsJohn D. Bookstaver
St. Charles Community College
St. Peters, MO
2006, Prentice Hall, Inc.
Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten
Attractions
Intra–(strong)
Inter–(weak)
“Bonds” “IMAFs”
??
?
Ionic(metal–
nonmetal)
Covalent(nonmetals)
polarnon-polar
Intermolecular Attractive Forces
Intramolecular Attraction (within)
(strong bonds)
(weak)
Intermolecular Attraction (between)
Which attraction is overcome (broken) by
melting & vaporizing? weak IMAFs
between molecules
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Intermolecular Attractive Forces
IMAFs determine physical properties
such as boiling & melting points, vapor pressure, and viscosity.
bp, mp,
vp, visc.
Intramolecular Attraction (within)
(strong bonds)
(weak)
Intermolecular Attraction (between)
States of MatterThe main difference between phases of
matter is the distance between particles.
States of MatterState (distance between particles) at a certain
T and P depends on two opposing qualities:
IMAFs
(intermolecular attractive forces
between particles)
KE
(kinetic energy of the particles
vs.
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Attractions
Intra–(strong)
Ionic(metal–
nonmetal)
Covalent(nonmetals)
polar non-polar
Inter–(weak)
“Bonds” “IMAFs”
?
At that instant, the He atom is
polar (instantaneous dipole).
(excess of e–’s on one side, and
shortage on the other)
Electrons in the 1s orbital of He
repel each other, BUT…
they occasionally wind up on
the same side of the atom.
London Dispersion Forces
δδδδ−−−− δδδδ++++
London Dispersion Forces
instantaneous
dipole
induced
dipole
causes
LDFs:attractions between instantaneous dipoles
and induced dipoles caused by motion of e–’s.
δδδδ−−−− δδδδ++++ δδδδ−−−− δδδδ++++
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London Dispersion Forces
• present in all molecules, (polar & nonpolar)
• The tendency of an electron cloudto distort to become temporarily polar in this way is called ___________.polarizability
δδδδ−−−− δδδδ++++ δδδδ−−−− δδδδ++++
Factors Affecting London Forces
• LDFs increase with increased MW b/c…
larger e– clouds, are more polarizable.
(use this phrase to answer FR question)
MW (molecular weight)
Factors Affecting London Forces
• long, skinny
molecules have stronger IMAFs
due to…
…increasedsurface area to
form more
attractions.(SAcylinder > SAsphere)
Shape
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Attractions
Intra–(strong)
Ionic(metal–
nonmetal)
Covalent(nonmetals)
polar non-polar
Inter–(weak)
“Bonds” “IMAFs”
?London
dispersion
forces(nonpolar & all)
Dipole-Dipole Interactions
• Polar molecules with
permanent dipoles are attracted to each other.
(dipole) (dipole)
Dipole-Dipole Interactions
The more polar the molecule,
the higher the boiling/melting point.
(due to greater dipole-dipole IMAFs that
require more energy to overcome)
?
∆∆∆∆EN
polar bonds
assym. shape
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Which Have a Greater Effect:Dipole-Dipole Interactions or Dispersion Forces?
•dipole–dipole interactions (permanent dipoles)
are typically stronger than LDFs (temporary dipoles as instantaneous–induced).
•But much larger molecules could have LDFs that are stronger than dipole-dipole
interactions.
(larger e– clouds, are more polarizable)
Attractions
Intra–(strong)
Ionic(metal–
nonmetal)
Covalent(nonmetals)
polar non-polar
Inter–(weak)
London dispersion
forces(all, nonpolar)
dipole–dipole(polar)
“Bonds” “IMAFs”
?
nonpolar
polar
Boiling Points
How Do We Explain This?
•unusually high bp
•unusually strong IMAFs
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• H-bonds are caused by an
electron deficient H atoms (bonded to N, O, or F) attracted to
small, very electronegative
N, O, or F atoms on a nearby molecule.
Hydrogen Bonding
Attractions
Intra–(strong)
Ionic(metal–
nonmetal)
Covalent(nonmetals)
polar non-polar
Inter–(weak)
London dispersion
forces(all, nonpolar)
dipole–dipole(polar)
H–bondsH with
N, O, F?
“Bonds” “IMAFs”
Ion-Dipole Interactions
• ionic solutes dissolve in polar solvents
OH
H
O
H
H
Na+ Cl–
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Attractions
Intra–(strong)
Ionic(metal–
nonmetal)
Covalent(nonmetals)
polar non-polar
Inter–(weak)
London dispersion
forces(all, nonpolar)
dipole–dipole(polar)
H–bondsH with
N, O, F
ion–dipole(aq ions)
“Bonds” “IMAFs”
(ion–dipole)
Intermolecular Attractive Forces
Stronger
Weaker
H-bonds(if H with N, O, or F)
dipole-dipole int.’s(polar molecules)
London dispersion forces(nonpolar, instant–induced dipoles)
(ion–dipole)
HWp. 476 #1,2
• London dispersion forces (LDFs) only
• bp increases as length of chain b/c……larger e– cloud, more polarizable
Organic Functional Groups
Alkanes
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& H-bondpolar
polar
Organic Functional Groups
What IMAFs?
& H-bond
Organic Functional Groups
What IMAFs?
polar
polar
polar
polar & H-bond
H-bond
3–pentanone(ketone)
propanal (aldehyde)
ethylamine(amine)
ethanoic acid (carboxylic acid)
trimethylamine(amine)
dipole-dipole
dipole-dipole
dipole-dipole
H-bondbutane(alkane)
LDFs
ethanol(alcohol)
H-bond
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IMAFs in Protein Structure & DNA
aminoacid
protein
IMAFs in Protein Structure & DNA
hold, but can be
broken
HWp. 476
#14-26
Intermolecular Forces Affect
Many Physical Properties
The strength of the
attractions between particles can greatly
affect the physical
properties of a substance or solution.
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Cohesive
• to each other
Adhesive
• to surface
Cohesive/Adhesive Forces
cohesive
adhesive
glass
Capillary Action
• due to co/adhesive forces
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results from the
net inward forceexperienced by the
molecules on the
surface of a liquid.
Surface Tension
• resistance of a liquid to flow
• increases with IMAF’s and decreases with higher temp.
Viscosity
HW p. 479 #29
Phase ChangesHW p. 479
#34
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• Heat of Fusion (Hfus):
energy to change (s) to (l) at melting point.
Energy and Phase Changes
Energy and Phase Changes
• Heat of Vaporization (Hvap):
energy to change (l) to (g) at boiling point.
DEMO: butane
What happens to added KE?
Energy and Phase Changes
HW
p. 480 #35,
47aTemp. does not change
during phasechange.
Added energy
separates particles
(overcome
IMAFs)(↑↑↑↑PE)
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liquid molecules
escape to vapor
Vapor Pressure
more volatile
=more vapor
pressure above liquid
gas molecules
condense to liquid
(dynamic equilibrium)
=
_____ IMAFSweak
Vapor Pressure
• As T ↑, the fraction of molecules that have enough energy to escape increases.
As more molecules escape the liquid, the
pressure they exert increases.
Dynamic Equilibrium:vaporize/condense at same rate
Vapor Pressure
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Vapor Pressure
•boiling point:
T at which vapor pressure
=
atmospheric pressure
•normal b.p.:
T at whichv.p. = 1 atm
HW p. 480 #47b, 48
DEMO: boil H2O
Solutions
• homogeneous mixtures of
pure substances.
• solute is dispersed uniformly
throughout the solvent.
+
Why does stuff dissolve?
IMAFs between
solute–solventmust be
stronger
IMAFs between
solute–solutesolvent–solvent
solvated
(dissolved)
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For Ionic Solutes…
Ions are soluble in water because ion-dipoleattractions are strong enough to overcome the
crystal lattice energy of the ionic solid salt.
Energy Changes in Solution
separation of solute
(absorb = endothermic)
separation of solvent
(absorb = endothermic)
attractions between solute and solvent
(release = exothermic)
Calcium Chloride Ammonium Chloride
CaCl2 NH4Cl
feels _______ feels ______
Heat flows where?
into or out of ? into or out of ?
warmer cooler
Demo
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H+
+ +
+
+–
–
–
enthalpy(heat)
∆H(final – initial)
Why Do
EndothermicProcesses Occur?
Usually favorable
processes tend to lower energy.
∆E = – (exo or release)
But in some processes,
heat is absorbed, not released.
+
+
+
–
How?
EntropyEntropy (S):
∆S = (final – initial)
∆S = (more – less)
∆S = +
• increasing the entropy (dispersal) (∆S = +) by
mixing lowers the energy (∆E = –) of a system (even if ∆H = +).
(less dispersal) (more dispersal)
+∆H (absorb heat)(+∆E)
+∆E (raised)
+∆S (gain entropy)(–∆E)–∆E (lowered)
dispersal of matter & energy
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• Unsaturated
�Less than the maximum
dissolved at that
temperature.
Types of Solutions
Types of Solutions
• Saturated
�Solvent holdsmaximum solute
possible at that
temperature.
�Dissolved solute is in
dynamic equilibriumwith solid solute
particles.
• Supersaturated
�More solute than is normally possibleat that temperature.
�unstable; crystallization is stimulatedby a “seed crystal” or scratching.
Types of Solutions
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Factors Affecting Solubility
• “like dissolves like”: (similar IMAFs)
�Polar substances dissolve in polar solvents.
H2O CH3Cl CH3CH2OH NH3
�Nonpolar dissolve in nonpolar solvents.
C6H14 CCl4 I2
�similar IMAFs are more soluble.
Which is more soluble in water (H2O) and
which is more soluble in hexane (C6H14)
HW p. 566 #12,14,18
Gases in Solution
• In general, the solubility of gases in water
increases with increasing size. …WHY?
• Larger molecules have larger e– clouds
stronger dispersion forces.
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Gases in Solution• The solubility of gas in liquid is
directly proportional to pressure.
Gases are
more soluble:Low T
High P
1) Highest solubility at
20oC? 30oC?
solubility of solids inc. with temp.
Solubility
Curves
HW p. 566 #20,23,25
2) How many grams
KClO3 at 70oC ?
3) Is 50 g of KCl at 50oC
sat, unsat, or supersat?
30 g of NaCl at
30oC?
The greater the IMAFs,…
the _______ the bp and mp.
the _______ the cohesion/adhesion.
the _______ the surface tension.
the _______ the viscosity.
the _______ the vapor pressure (volatility)
Intermolecular Forces Affect
Many Physical Properties
greater
greater
greater
greater
lower
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Which has a higher boiling point? Explain.
CF4 vs. CH3OCH3
CF4 has London dispersion forces and
CH3OCH3 has dipole-dipole interactions.
Stronger intermolecular attractive forces in
CH3OCH3 require more energy to overcome.
Intermolecular Forces Affect
Many Physical Properties
Attractions
Intra–(strong)
Ionic(metal–
nonmetal)
Covalent(nonmetals)
polar non-polar
Inter–(weak)
London dispersion
forces(all, nonpolar)
dipole–dipole(polar)
H–bondsH with
N, O, F
ion–dipole(aq ions)
“Bonds” “IMAFs”
mp’s & bp’smp’s (of solids)
4 Types of Bonding in Solids�Ionic [metal–nonmetal]
• transfer e–’s forming attractive charged ions
�Covalent [nonmetals]
• sharing e–’s in mutual nuclear attraction
�Covalent Network [C(d)]
• shares e–’s throughout
�Metallic [metals]
• metal atoms bonded by delocalized val. e–’s
Diamond
Quartz
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Ionic Solids
• Strong Ionic Bonds in a crystal lattice of
+/– ions bonded by electrostatic attraction.
�hard and brittle
�high melting points
�conduct in solution(aq) or molten(l)
(Coulombic)
(ordered)
E = κκκκq1q2
d
stronger
attraction
more q
less d
more
energyto break
Covalent (Molecular) Solids
• Weak IMAF’s (LDF’s, dipole-dipole, H-bonds)
�softer
�lower melting points
C(graphite)
Covalent-Network Solids
• Strong Covalent Bonds throughout.
C(diamond) WC2 (carbide) SiO2 (quartz)
�Very hard�Very high melting points
C(graphite) C(diamond)
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Metallic Solids
• Metals are not
covalently bonded, but attractions are
too strong to be
IMAFs.
• Metallic Bonds
�delocalized valence “sea” of electrons.�Excellent conductors
�Malleable and Ductile (“smooshable”)
�soft to very hard�low to very high m.p.’s
Alloys
Alloys:
Homogeneous metallic mixtures (solutions) by mixing melted metals in the liquid phase.
Brass Steel
67%Cu, 33%Zn
80%Fe, 0.4%C,
18%Cr, 1%Ni
Attractions:
Held together mainly by metallic bondingdue to a delocalized sea of electrons.
AlloysBrass Steel
• at. radius: similar
• density: in between
• malleability: similar
Substitutional:• at. radius: different
(smaller fits between larger)
• density: greater(more mass in same volume)
• malleability: less (harder)
Interstitial:
Fe Fe Fe Fe
Fe Fe Fe
Fe Fe Fe Fe
C
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Attractions in Solids, Liquids, & Solutions
Molecular
Covalent-Network
Ionic
Metallic
Soft
Low mp & bp
Poor conductor
Very hard
Very high mp
Poor conductor
Hard and brittle
High mp
Conducts as (aq) or (l)
Soft to very hard
Low to very high mp
Conductor, Malleable, Ductile
Ar I2 CO2 H2O
C2H5OH C11H22O11
C(diamond)
SiO2
WC2
NaCl
CuSO4
All metals
& alloys: Cu, Fe, K, Al,…
Covalent Bonds (network)C(diamond) , SiO2 (quartz) ,
WC2 (tungsten carbide) , etc…
Ionic Bondscrystal lattice of
charged ions
Intermolecular Attractions (IMAFs)London dispersion forces
Dipole-dipole interactions
Hydrogen bonds
Type Forces Between Particles Properties
δδδδ−−−− δδδδ++++
−−−− ++++
Solutions Solute-Solvent Attractions
similar IMAFs or ion–dipole(l) + (l),
(s) + (l) = (aq)
q1q2
d
(nonpolar)
(polar)
(H with N, O, F)
Metallic Bondsdelocalized “sea” of val. e–’s
Molecular (IMAFs)
Hydrogen bonds(if H with N , O , or F)
Dipole-dipole interactions(polar molecules)
London dispersion forces(all molecules & nonpolar)
instant/induced dipoles)
Ionic Bonds(attractions between +/– ions)
Attraction or Bond Stronger with:
greater ∆EN
N < O < F
greater ∆ENgreater dipole moment
larger e– cloud,
more polarizable
greater q, less d(Coulombic attraction)
Molecular (IMAFs)
The Stronger the Attractions, the…
higher mp of solid (higher ∆∆∆∆Hfus)
harder solid
higher bp of liquid (higher ∆∆∆∆Hvap)
higher viscosity of liquid
lower vapor pressure of liquid (more volatile)
more soluble (similar solute-solvent IMAFs)
Attractions Affect
Physical Properties
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Reasoning with Concepts
1) Identify attractions
(Bonds? IMAFs?)
2) Compare strength
3) Connect to energy (abs./rel.)
and/or physical property
+ –
