Liquids and Solids - UCSBdevries/khem/notes/10a forces...Plasmas – The fourth phase of matter Only...

Liquids and SolidsSolids

Red Beryl, Be3Al2Si6O18-

Copyright © Houghton Mifflin Company. All rights reserved. 16a–2

A Molecular Comparison of Liquids and A Molecular Comparison of Liquids and SolidsSolidsSolidsSolids

High Entropy, S0gas Lower Entropy, S0

liquid Smallest Entropy, S0solid


Figure 16.47: The number of molecules in a liquid with a given energy versus kinetic energy at two temperatures.


Figure 16.50: The heating curve for a given quantity of water where energy is added at a constant rate.gy


Figure 16.55: The phase diagram for water


The 3 Most CommonStates “of Earthbound Creatures”Plasmas – The fourth phase of matter

Only ions and electrons

106 K

Pl Ph F

More ions,

lots of electrons

104 KPlasma Phase Forms

Some ions and electrons

103 K

Atoms - Molecules

Dissociate

102 K

Gas Phase Atoms/Molecules

10 KLiquid Phase Atoms/Molecules


0 K Solid Phase Crystals, Networks

The Sun – 99.8% Mass of Solar System, Plasma

15 x 106 K

5 x 106 K

15,000 K

Copyright © Houghton Mifflin Company. All rights reserved. 16a–95800 K

105 K

InterIntermolecular Forcesmolecular Forces• The covalent bond holding a molecule together is an

intramolecular force.• The attraction between molecules is an intermolecular

force.• Intermolecular forces are much weaker than

intramolecular forces (e.g. 16 kJ/mol vs. 431 kJ/mol for HCl).

• When a substance melts or boils the intermolecular forces b k ( h l b d )are broken (not the covalent bonds).

• When a substance condenses intermolecular forces are f d


formed.

Larger INTERmolecular forces →

• Higher melting pointHigher melting point• Higher boiling point

h l f f i• Larger enthalpy of fusion


Intermolecular ForcesIntermolecular Forces

+ -+ -


Table of Force EnergiesTable of Force Energies

Type of Force Energy (kJ/mol) I i B d 300 600Ionic Bond 300-600Covalent 200-400H d B di 20 40Hydrogen Bonding 20-40Ion-Dipole 10-20Di l Di l 1 5Dipole-Dipole 1-5Instantaneous Dipole/I d d Di l 0 05 2


Induced Dipole 0.05-2



Intermolecular ForcesIntermolecular ForcesII i Fi FIonIon--ion Forcesion Forces

QQ2

21d

QQkF =

• F increases as Q increases and as d decreases:– the larger the charge and smaller the ion, the larger the


g g gattraction.

Intermolecular ForcesIntermolecular ForcesII Di l FDi l FIonIon--Dipole ForcesDipole Forces

• Interaction between an ion (e.g. Na+) and a dipole (e.g. water).

QQ2

21d

QQkF =

– Since Q1 is a full charge and Q2 is a partial charge, F is comparatively large.p y g

• F increases as Q increases and as d decreases:– the larger the charge and smaller the ion, the larger the ion-


dipole attraction.


DipoleDipole--Dipole ForcesDipole Forces

• Dipole-dipole forces exist between neutral polar molecules.

• Polar molecules need to be close together.g• Weaker than ion-dipole forces:

21QQ2

21d

QQkF =


– Q1 and Q2 are partial charges.

Dipole-Dipole Forces



DipoleDipole--Dipole ForcesDipole Forces• There is a mix of attractive and

repulsive dipole-dipole forces asrepulsive dipole dipole forces as the molecules tumble.

• If two molecules have about the• If two molecules have about the same mass and size, then dipole-dipole forces increase withdipole forces increase with increasing polarity.


Intermolecular ForcesIntermolecular ForcesL d Di i FL d Di i FLondon Dispersion ForcesLondon Dispersion Forces

• Weakest of all intermolecular forces• Weakest of all intermolecular forces.• The nucleus of one molecule (or atom) attracts the electrons of the

adjacent molecule (or atom).• For an instant, the electron clouds become distorted.• In that instant a dipole is formed (called an instantaneous dipole).• Polarizability is the ease with which an electron cloud can be

deformed.• The larger the molecule (the greater the number of electrons) the• The larger the molecule (the greater the number of electrons) the

more polarizable.



L d Di i FL d Di i FLondon Dispersion ForcesLondon Dispersion Forces


London Dispersion Forces


London Dispersion

Forces



London Dispersion ForcesLondon Dispersion Forces

• London dispersion forces increase as molecular weight increases.p g• London dispersion forces exist between all molecules.• London dispersion forces depend on the shape of the molecule.• The greater the surface area available for contact, the greater the

dispersion forces.L d di i f b t h i l l l l• London dispersion forces between spherical molecules are lower than between sausage-like molecules.


Intermolecular ForcesIntermolecular ForcesLondon Dispersion ForcesLondon Dispersion ForcesLondon Dispersion ForcesLondon Dispersion Forces

London dispersion forces between spherical molecules are lower than between sausage-like molecules


H-Bonding

Occurs when Hydrogen is attached to aOccurs when Hydrogen is attached to a highly electronegative atom (O, N, F).

N-H… N- O-H… N- F-H… N-

N H O O H O F H ON-H… O- O-H… O- F-H… O-

N-H… F- O-H… F- F-H… F-

δ+ δ-


Requires Unshared Electron Pairs of Highly Electronegative Elements

Hydrogen Bonding in Water MoleculesWater Molecules


Why Does Ice Float?Why Does Ice Float?

D2O(s) H2O(s)



Structure of IceObserve the orientation of the

Hydrogen Bondsy g


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The Boiling Points of the Covalent Hydrides of the Elements in Groups 4A, 5A, 6A, and 7A


DNA Double Helix-Held Together with

H-Bonds


Three Components of DNA Structure

base: thymine(pyrimidine)monophosphate

sugar: 2’-deoxyriboseα

5’

(5’ to 3’) 3’1’

2’4’

3’ linkage

base:adenine(purine)

5’ linkage


no 2’-hydroxyl

g

Pyrimidines used in Base Pairs, DNA


6-membered rings only

Purines used in Base Pairs, DNA

Fused 5 and 6 member rings


g

DNA Base Pairing

A-T pairing

2 H Bonds2 H-Bonds

G-C pairing

3 H bonds


3 H-bonds

A-T and G-C Base Pairs Hold the DNA helices togetherg










Base Pairs Double Helix


Hydrogen-Bonding’s Role in DNA Structure


Table of Force EnergiesTable of Force Energies

Type of Force Energy (kJ/mol) I i B d 300 600Ionic Bond 300-600Covalent 200-400H d B di 20 40Hydrogen Bonding 20-40Ion-Dipole 10-20Di l Di l 1 5Dipole-Dipole 1-5Instantaneous Dipole/I d d Di l 0 05 2


Induced Dipole 0.05-2

Intermolecular Forces SummaryIntermolecular Forces Summary


Intermolecular IntramolecularCopyright © Houghton Mifflin Company. All rights reserved. 16a–48

Which forces?

London Dipole H-bond ionicXe XCH4 XCO2 XCO X XHBr X XHF X XCH3OH X XNaCl X


NaCl XCaCl2 X

Relative forces

I2 Cl2>LargerL d

H2S H2O>London

< H-bond

CH3OCH3 CH3CH2OH< H-bond

CsBr Br2

CO CO l

>ionic

CO2 CO

SF2 SF6

< polar

>polar


2 6>polar

Some Properties of LiquidsSome Properties of LiquidsVi itVi itViscosityViscosity• Viscosity is the resistance of a liquid to flow.• A liquid flows by sliding molecules over each

other.• The stronger the intermolecular forces, …….

the higher the viscositythe higher the viscosity.


Some Properties of LiquidsSome Properties of LiquidsVi itVi itViscosityViscosity• Viscosity is the resistance of a liquid to flow.• A liquid flows by sliding molecules over each

other.• The stronger the intermolecular forces, …….

the higher the viscositythe higher the viscosity.

Surface TensionSurface Tension• Bulk molecules (those in the liquid) are equally


Bulk molecules (those in the liquid) are equally attracted to their neighbors.

A molecule in the interior of a liquid is attracted to the molecules surrounding it, whereas a molecule at the surface of liquid is attracted

only by molecules below it and on each side of it.only by molecules below it and on each side of it.


Some Properties of LiquidsSome Properties of LiquidsS f T iS f T iSurface TensionSurface Tension


Some Properties of LiquidsSome Properties of LiquidsS f T iS f T iSurface TensionSurface Tension


Water Strider (Hemiptera: Gerridae)


Surface Tension Mercury

Surface tension is the amount of energy required to increase


Surface tension is the amount of energy required to increase the surface area of a liquid.

Some Properties of LiquidsSome Properties of LiquidsS f T iS f T iSurface TensionSurface Tension• Meniscus is the shape of the liquid surface.

– If adhesive forces are greater than cohesive forces, the liquid surface is attracted to its container more than the bulk molecules. Therefore, the meniscus is U-shaped (e.g. water in glass).f h i f h dh i f h– If cohesive forces are greater than adhesive forces, the

meniscus is curved downwards.C ll A Wh l b i• Capillary Action: When a narrow glass tube is placed in water, the meniscus pulls the water up h b


the tube.

Water (left) has a downward curving meniscus Mercury (right)


Water (left) has a downward curving meniscus.Mercury (right) has an upward curving meniscus

Capillary ActionCapillary ActionThe tendency of certain liquids to rise in aThe tendency of certain liquids to rise in aThe tendency of certain liquids to rise in a The tendency of certain liquids to rise in a

narrow tube.narrow tube.

There is a There is a competition competition b tb tbetween between adhesive and adhesive and cohesive cohesive forces.forces.


forces.forces.

Larger INTERmolecular forces →

• Higher melting pointHigher melting point• Higher boiling point

h l f f i• Larger enthalpy of fusion

•Larger viscosity•Higher surface tensionHigher surface tension•Smaller vapor pressure

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