5.2.00 4:24 PM1 11.1 Intermolecular Forces Keeping Matter Together Nature’s Forces.

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11.1 Intermolecular Forces11.1 Intermolecular ForcesKeeping Matter TogetherKeeping Matter Together

Nature’s ForcesNature’s Forces

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Phases of Matter: TerminologyPhases of Matter: Terminology

Energy is required for phaseEnergy is required for phasechange to occur.change to occur.

Solid-Liquid-GasSolid-Liquid-GasTriangleTriangle

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Heating Cooling CurveHeating Cooling CurveFrom Steam to Ice and Vice-versaFrom Steam to Ice and Vice-versa

6.01 kJkJmolmol

80 80 calcal gg

6.01 kJkJmolmol

80 80 calcal gg

40.6740.67 kJ mol

540 cal g

40.6740.67 kJ mol

540 cal g

4.184 J g °

1 cal g o

4.184 J g °

1 cal g o

How much energy of 1g HHow much energy of 1g H22O 100°C to 0°C ?O 100°C to 0°C ?How much energy of 1g HHow much energy of 1g H22O 100°C to 0°C ?O 100°C to 0°C ? 540+100+80=720cal540+100+80=720cal540+100+80=720cal540+100+80=720cal

2.09 2.09 JJg °g °

0.50 0.50 calcal g °g °

2.09 2.09 JJg °g °

0.50 0.50 calcal g °g °

1.84 1.84 JJg °g °

0.43 0.43 calcal g °g °

1.84 1.84 JJg °g °

0.43 0.43 calcal g °g °

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At the molecular level:At the molecular level:

Molecules or matter is held together by attractive force Molecules or matter is held together by attractive force “glue” called intermolecular forces“glue” called intermolecular forces

Intermolecular ForcesIntermolecular Forces

Energy added (K.E. increase)

SOLID LIQUID GAS

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Intramolecular Forces -Intramolecular Forces -Force which keeps integrity of molecule together, i.e., bonds or electrostatic bonding.Force which keeps integrity of molecule together, i.e., bonds or electrostatic bonding.

Intermolecular Forces -Intermolecular Forces -Attractive force between molecules. Responsible for keeping matter in solid or liquid phaseAttractive force between molecules. Responsible for keeping matter in solid or liquid phase

Keeping Matter togetherKeeping Matter together

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The Forces be with YouThe Forces be with You2 Basic types of Intramolecular Force2 Basic types of Intramolecular Force

Ion - ion - Electrostatic attractionIon - ion - Electrostatic attraction

Covalent Bonds - Mutual sharing of electronsCovalent Bonds - Mutual sharing of electrons

4 Basic types of Intermolecular Force*4 Basic types of Intermolecular Force*1. Ion - dipole : Ion is attracted to polar molecule1. Ion - dipole : Ion is attracted to polar molecule

2. dipole - dipole: Polar molecules attracted to each 2. dipole - dipole: Polar molecules attracted to each other.other.

3. dipole - induce dipole: Polar molecules attracted 3. dipole - induce dipole: Polar molecules attracted to nonpolar molecules.to nonpolar molecules.

4. induce dipole -induce dipole (Van der Waal’s 4. induce dipole -induce dipole (Van der Waal’s forces – also called London dispersion forces) forces – also called London dispersion forces) nonpolar molecules attraction for each other due to nonpolar molecules attraction for each other due to electron cloud distortion.electron cloud distortion.

* plus one

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Relative StrengthRelative Strength

InteractionInteraction Example Example EnergyEnergy

ion- ionion- ion NaNa++ Cl Cl-- 400 -4000 kJ/mol400 -4000 kJ/mol

Covalent Bonds Covalent Bonds H - HH - H 150-1100 kJ/mol150-1100 kJ/mol

ion-dipole (I-D)ion-dipole (I-D) Na Na++ H H22OO 40-600 kJ/mol40-600 kJ/mol

dipole - dipole (D-D)dipole - dipole (D-D) ICl ICl ICl ICl 5-25 kJ/mol5-25 kJ/mol

dipole - dipole - induce dipole (D-ID)induce dipole (D-ID) HCl O HCl O22 2-10 kJ/mol2-10 kJ/mol

Van der Waal Van der Waal N N22 N N22 00.05 - 40 kJ/mol.05 - 40 kJ/mol

• • H-Bond (10 - 40 kJ/molH-Bond (10 - 40 kJ/mol

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Ion - Ion: Electrostatic attraction between ionsIon - Ion: Electrostatic attraction between ions

Covalent Bonds: Bond between atoms as a result of electrons sharing.Covalent Bonds: Bond between atoms as a result of electrons sharing.

Ion - Ion Ion - Ion Covalent BondsCovalent Bonds

F-F

9 p 10 n

Na+Na

11 p 12 n

11 p 12 n

9 p 10 n

11 p 12 n

9 p 10 n

NaF

F

9 p 10 n

9 p 10 n

F

9 p 10 n

9 p 10 n

F2

Bond Energy: = 926 kJ/mol

Bond Energy: = 159 kJ/mol

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Ion - Dipole: Ion - Dipole: Charge and size dependent.

Most important for larger charge and small ionic radius.

Ion - DipoleIon - Dipole

Cation Ion Radius HHyd (kJ/mol)Li+ 90 -515Na+ 116 -405K+ 152 -321RB+ 166 -296Cs+ 181 -268

Cation Ion Radius HHyd (kJ/mol)Li+ 90 -515Na+ 116 -405K+ 152 -321RB+ 166 -296Cs+ 181 -268

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Dipole - DipoleDipole - DipoleDipole - Dipole: Dipole - Dipole: A permanent attractive intermolecular force resulting

from the interaction of the positive end of one molecule with the negative end of another.

Occurs between identical or different polar molecules.

NonPolar Polar M(g/mol) bp (°C) M (g/mol) bp(°C)N2 28 -196 CO 28 -192SiH4 32 -112 PH3 34 -88GeH4 77 -90 AsH3 78 -62Br2 160 59 ICl 162 97

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Induce dipole - induced dipole: Induce dipole - induced dipole: Vander Waal’s forcesVander Waal’s forces

Van der Waal Van der Waal (Induced dipole-Induced dipole)(Induced dipole-Induced dipole)::Intermolecular force responsible for keeping nonpolar molecules (species) together.

Polarisability - Polarisability - The ease of which an e- cloud can be distorted. Larger the atomic size, the greater the number of electrons, the greater the polarizability.

Boiling Point of the Halogens and Noble Gases

Halogen B.pt (K) Noble Gas B.pt (K)

F2 85.1 He 4.6

Cl2 238.6 Ne 27.3

Br2 332.0 Ar 87.5

I2 457.6 Kr 120.9

Xe 166.1

Boiling Point of the Halogens and Noble Gases

Halogen B.pt (K) Noble Gas B.pt (K)

F2 85.1 He 4.6

Cl2 238.6 Ne 27.3

Br2 332.0 Ar 87.5

I2 457.6 Kr 120.9

Xe 166.1

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Boiling point versus polarisabilityBoiling point versus polarisability

Graphs for noble gases Graphs for noble gases and for series of nonpolar and for series of nonpolar molecules; both show a molecules; both show a family smooth increase of family smooth increase of boiling point with atomic boiling point with atomic weight (larger degree of weight (larger degree of polarisability) due to polarisability) due to increasing Van der Waal increasing Van der Waal forcesforces

How about HHow about H22Te, (-20°C) Te, (-20°C)

HH22Se, HSe, H22S, HS, H22OO Molar Mass

Kr

He

SiH4

GeH4

SnH4

CH4

-250°C

-100°C

0°C

Tem

pera

ture

-200°C Ar

Ne

Xe

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Boiling point Hydrogen compoundsBoiling point Hydrogen compounds

Graphs for family of Graphs for family of hydrogen containing hydrogen containing compounds and their compounds and their boiling point. In boiling point. In general there is an general there is an increase in the boiling increase in the boiling point except for Hpoint except for H22O, O,

HF and NHHF and NH33. Why? . Why?

There must be some There must be some other force that other force that operate on these operate on these compounds which compounds which increases their increases their intermolecular forces.intermolecular forces.

Molar Mass (Period)

H2Te

H2Se

H2O

SiH4

SbH3

GeG4

CH4

-100°C

0°C

100°C

Tem

per

atur

eHI

SnH4

HF

NH3

PH3

AsH3HCl HBr

H2S

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H-Bonding: H-Bonding: A special glue above and beyond dipole-dipole intermolecular forces.

H-bonding is a strong type of intermolecular force (bond) H-bonding is a strong type of intermolecular force (bond) between hydrogen and very electronegative elements ( 4 between hydrogen and very electronegative elements ( 4 - 30 kJ/mol). - 30 kJ/mol).

NN-H-H OO-H-H FF-H-H sometimessometimes ( (ClCl-H)-H)

Bichemical structural Integrity.Bichemical structural Integrity.

Water possesses H-bond: Responsible for water’s unique Water possesses H-bond: Responsible for water’s unique properties.properties.

A Special Type of BondingA Special Type of BondingH-BondingH-Bonding

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Example: H-bondingExample: H-bondingWhich of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate.Which of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate.

a) Ca) C22HH66 d) Hd) H33CCOOHCCOOHNoNo YesYes

b) CHb) CH33OHOH e) He) H33CCHCCH22OHOHYesYes YesYes

c) Hc) H33CCONHCCONH22 f) Hf) H33CCOCHCCOCH33YesYes NoNo

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Biological IntegrityBiological Integrity

H-bonding is responsible for the structural integrity of Biological molecules.• Protein structures • DNA and RNA

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Water is a liquid Water is a liquid at at room temperature as a room temperature as a direct consequence of direct consequence of hydrogen bonding hydrogen bonding between adjacent water between adjacent water molecules. molecules. (Most other molecules with (Most other molecules with comparable Molar mass is a comparable Molar mass is a gas at room temperature)gas at room temperature)

Pure water is a liquid Pure water is a liquid between 0°C and between 0°C and 100°C.100°C.

HH22O: Nature of WaterO: Nature of Water

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ExampleExampleIdentify the dominant intermolecular forces for each of the following substances, and select the substance with the higher boiling point in each Identify the dominant intermolecular forces for each of the following substances, and select the substance with the higher boiling point in each pair;pair;

a) MgCla) MgCl2 2 or PClor PCl33 b) Hb) H33CNHCNH22 or CH or CH33FF

ion-dipole ion-dipole dipole-dipoledipole-dipole H-bond H-bond dipole-dipoledipole-dipole

VdWVdW VdWVdW dipole-dipole dipole-dipole VdWVdW

Higher BptHigher Bpt VdWVdW

Higher BptHigher Bpt

b) CHb) CH33OH or CHOH or CH33CHCH22OH OH e) Hexane or cyclohexanee) Hexane or cyclohexane

H-bondH-bond H-bond H-bond VdW VdW VdW VdW

dipole-dipole dipole-dipole dipole-dipole dipole-dipole Higher BptHigher Bpt

VdW VdW VdW VdW More surface areaMore surface area

Higher BptHigher Bpt

Higher MWt.Higher MWt.

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Overview: Recognizing Intermolecular ForcesOverview: Recognizing Intermolecular ForcesFlowchart for recognizing the major types of intermolecular forces. Van der Waal’s forces occur Flowchart for recognizing the major types of intermolecular forces. Van der Waal’s forces occur in all instances. The strength of other forces generally increases proceeding from left to rightin all instances. The strength of other forces generally increases proceeding from left to right

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Bonding forces are Bonding forces are relatively strong because relatively strong because they involve larger they involve larger charges that are closer charges that are closer together. Ionic (400-together. Ionic (400-4000 kJ/mol) Metallic 4000 kJ/mol) Metallic (75-1000 kJ/mol)(75-1000 kJ/mol)

Intermolecular forces are Intermolecular forces are relatively weak because relatively weak because they typically involve they typically involve smaller charges that are smaller charges that are farther apart. H-bond farther apart. H-bond (10-40 kJ/mol) LDF (10-40 kJ/mol) LDF (0.05 - 40 kJ/mol)(0.05 - 40 kJ/mol)

Summary of Nature’s ForcesSummary of Nature’s Forces