IB Chemistry on Polarity, Hydrogen Bonding and Van Der Waals forces

http://lawrencekok.blogspot.com

Prepared by Lawrence Kok

Tutorial on Polarity, London Forces and Hydrogen Bonding.

Chemical Bonds

Ionic Bonds

Transfer of electron from metal to non metal

Metal donate e Non Metal accept e

Positive ion (cation)

Negative ion (anion)

Ionic compound

+ -electrostatic forces attraction

Chemical Bonds

Ionic Bonds





Ionic compound

Covalent BondsSharing of electron bet non metal atoms

Equal sharing electrons


Polar covalent Bonds Non Polar covalent Bonds

Unequal sharing electrons

Covalent Polar Non polar

Chemical Bonds

Ionic Bonds





Ionic compound

Covalent BondsSharing of electron bet non metal atoms

Equal sharing electrons


4 0.4 0Difference in electronegativity

2

EN - 0.9 EN – 3

Diff = (3 – 3 ) = 0

H

EN – 2.1

Diff = 3 – 0.9 = 2.1

Polar covalent Bonds Non Polar covalent Bonds

Unequal sharing electrons

Covalent Polar Non polar

CI CI

EN – 3

Covalent Non polar

CI

Covalent polar Ionic

EN – 3

Diff = (3 – 2.1 ) = 0.9

Na+ CI-

EN – 3

Shared electron cloud closer to O

Electronegativity

Electronegativity (EN)•Tendency of atom to attract/pull shared/bonding electron to itself•EN value higher – pull/attract electron higher (EN value from 0.7 – 4)

Electronegativity•EN increase up a Group•EN increase across a Period


Electronegativity



H2.2

Li Be B C N O F

CI

Br

I

1 1.6 2 2.6 3 3.4 4

Electronegativity values

N, O, F have high EN value

3.2

3

2.7

Molecule

Diff in EN Polarity

H - F (4.0 – 2.2) = 1.8 Most polar

H - CI (3.2 – 2.2) = 1

H - Br (3.0 – 2.2) = 0.8

H - I (2.7 – 2.2) = 0.5 Least polar

Polarity

Shape Diff in EN

Symmetrical Asymmetrical

Bond polarity cancel out each other

Polar bonds – molecule NON POLAR


Polar bonds – molecule POLAR✓✗


Electronegativity



H2.2

Li Be B C N O F

CI

Br

I

1 1.6 2 2.6 3 3.4 4

Electronegativity values

N, O, F have high EN value

3.2

3

2.7

Molecule

Diff in EN Polarity

H - F (4.0 – 2.2) = 1.8 Most polar

H - CI (3.2 – 2.2) = 1

H - Br (3.0 – 2.2) = 0.8

H - I (2.7 – 2.2) = 0.5 Least polar

Polarity

Shape Diff in EN

Symmetrical Asymmetrical


Polar bonds – molecule NON POLAR


Polar bonds – molecule POLAR

Lewis structure

VSEPR

Geometry

1

4 ECC3 bond pair1 lone pair

..N

H

HH

Polarity

2

3

4

Polar

✓✗

Covalent Bonds

Polar covalent Bonds Non Polar covalent Bond

Equal sharing electronUnequal sharing electron

Sharing of electron

Separation of charges

Unequal distribution electron due to diff EN value

shared electron closer to Oshared electron closer to F

Covalent Bonds



Sharing of electron

Formation electric dipole

Partial +/-

Dipole moment towards O

Partial + ( δ+)

Partial – (δ−)

Net dipole moment

Net Dipole moment

Polar covalent Bonds

Molecule polar ✓

O

O

✗

In presence of electric field

Separation of charges

Unequal distribution electron due to diff EN value

shared electron closer to Oshared electron closer to F

Covalent Bonds



Sharing of electron

Formation electric dipole

Partial +/-

Dipole moment towards O

Partial + ( δ+)

Partial – (δ−)

Net dipole moment

Molecule is polar (dipole)

Net Dipole moment

Measured in Debye

Turning force / Dipole moment = Force x DistancePolar covalent Bonds

+ -OIIIC δ+

δ-

Turning force – dipole moment

+ -

OIICIIO

δ+

δ-

δ-

No Turning force – No dipole moment

✓

Molecule polar ✓

O

O

Polarity

Shape

Asymmetrical

Shape

Symmetrical

Polar bonds

CI Polar bonds

δ-

δ+ δ+

δ+

δ-

δ-

δ-

δ- δ-

δ-

Asymmetrical Symmetrical

δ- δ+

Polar bonds

δ- δ-

Polar bonds

I

Polarity

Shape

Asymmetrical

Shape

Symmetrical

Polar bonds

CI Polar bonds

δ-

δ+ δ+

δ+

δ-

δ-

δ-

δ- δ-

δ-

Bond polarity don’t cancel

Bond polarity cancel

H

Net Dipole moment No Net Dipole moment

✗


δ- δ+

Polar bonds


Net Dipole moment

C O

δ- δ-

Polar bonds


No Net Dipole moment

✗ ✗✓✓

I

Polarity

Shape

Asymmetrical

Polar bond

Polarity dont cancel

(ASYMMETRICAL)

Net dipole moment

Molecule POLAR

Polar bond

Polarity cancel

(SYMMETRICAL)

NO net dipole moment

Molecule NON POLAR

Shape

Symmetrical

Polar bonds

CI Polar bonds

δ-

δ+ δ+

δ+

δ-

δ-

δ-

δ- δ-

δ-



H

Net Dipole moment No Net Dipole moment

✗


δ- δ+

Polar bonds


Net Dipole moment

C O

Polar bond

Polarity dont cancel

(ASYMMETRICAL)

Net dipole moment

Molecule POLAR

δ- δ-

Polar bonds


No Net Dipole moment

Polar bond

Polarity cancel

(SYMMETRICAL)

NO dipole moment

Molecule NON POLAR

✗ ✗✓✓

I

Bonding Forces

Bonding Forces within molecule Bonding Forces bet molecule

Intermolecular force bet molecule (IMF)Ionic bond

Covalent bond

Metallic bond

Permanent dipole

IonsMolecules/NOT ions

Ion dipole forcesPolar Non Polar

Hydrogen bonding

Temporary dipole(instantaneously induced dipole) London dispersion forces

Van Der Waals’ Forces attraction

Polar molecule (dipole – dipole attraction)

_ _ _ Attraction bet ions with polar molecules

Dipole/dipole attraction Dipole/dipole attraction

(involving H atom attach to N,O F)

Hydrogen bonding (dipole – dipole attraction)

Forces bet molecule

Permanent dipole

Polar Non Polar



Intermolecular force bet molecule (IMF)

Non polar molecules

Polar moleculesPolar molecules

Forces bet molecule

Molecules

Permanent dipole

Polar Non Polar



Polar molecule (dipole – dipole attraction)

Polar molecules due to diff in EN values

Dipole/dipole interaction

Electrostatic forces attraction bet molecules



H atom bond to electronegative atom, N, O, F

Partial H+ attracted to lone pair electron on N, O, F

Electrostatic force attraction bet molecules involve H


Non Polar molecule (Induced dipole attraction)

Random movement /distribution of electron

Instantaneous negative charge on atom

Induced a temporary dipole separation


Non polar molecules

Polar moleculesPolar molecules

Forces bet molecule

Molecules

Permanent dipole

Polar Non Polar



Molecules

Non polar moleculesPolar molecules

Polar molecules





Permanent dipole

Polar Non Polar


Polar molecule





Molecules





Instantaneous dipole in one atom induce a dipole in its neighbor



Polar molecules

Requirement for H bonding•H atom bonded to N, O, F•N, O, F - highly electronegative/ small size•Attract electron close to itself – Polarised H+

•N---H, O—H, F—H bonds VERY POLAR•Very polar H+ attract closely to lone pair on N, O, F

N ---- H O ---- H F ---- H δ- δ- δ- δ+ δ-+ δ+





Permanent dipole

Polar Non Polar



Polar molecule





Molecules





Instantaneous dipole in one atom induce a dipole in its neighbor



Polar molecules

Requirement for H bonding•H atom bonded to N, O, F•N, O, F - highly electronegative/ small size•Attract electron close to itself – Polarised H+

•N---H, O—H, F—H bonds VERY POLAR•Very polar H+ attract closely to lone pair on N, O, F

N ---- H O ---- H F ---- H δ- δ- δ- δ+ δ-+ δ+


Dipole – dipole attraction Induced – dipole attractionLondon dispersion forces

Polar Non Polar

All molecules have London dispersion forces due to uneven distribution of electron cloud

---

--

--

--

--

----

δ+ δ-London dispersion forces

London dispersion forces




Polar Non Polar


---

--

--

--

--

----




Factor affecting b/p of molecules

Temporary dipole attractionLondon dispersion force

Permanent dipole attractionDipole/dipole attraction

Hydrogen bonding

Types of forces/Bonding

Factors affecting VDF forcesIntermolecular force bet molecule (IMF)

Interaction Strength Boiling

Point/C

Covalent Strongest High

Ionic Strong High

Ion dipole Strong HIgh

Dipole- dipole (H bond)

Moderate High

Dipole – dipole Weak Low

Temporary induce dipole

(London dispersion)

Weakest Low


Polar Non Polar


---

--

--

--

--

----


RMM/Size Surface Area



N N

F F RMM – 38

RMM – 28

Size/ RMM increase

Number electrons increase

Temporary induced dipole increase

Van Der Waals bet molecule increase

RMM same

Surface area increase


Van Der Waals bet molecules increase

RMM – 72

RMM – 72

Pentane (C5H12)

Factor affecting b/p of molecules

Temporary dipole attractionLondon dispersion force


Hydrogen bonding

Factors affecting VDF forcesFactor affecting b/p of molecules


N N

F F RMM – 38

RMM – 28

Size/ RMM increase




RMM same




RMM – 72

RMM – 72

Pentane (C5H12)Temporary dipole attractionLondon dispersion force


Hydrogen bonding



N N

F F RMM – 38

RMM – 28

Size/ RMM increase




RMM same




RMM – 72

RMM – 72



Hydrogen bonding

H2 N2 CI2 H2O

RMM 2 28 71 18

BoilingPoint/C

-252 -196 -34 100

Forces London force

London force

London force

London forceDipole/dipoleHydrogen bonding

--

--

--

H2

London forces N2

London forces CI2

London forces H2OLondon forcesDipole/dipoleHydrogen bond

RMM increase - London force/VDF increase – boiling point increase

--

--

---

---

---

- --



N N

F F RMM – 38

RMM – 28

Size/ RMM increase




RMM same




RMM – 72

RMM – 72



Hydrogen bonding

H2 N2 CI2 H2O

RMM 2 28 71 18

BoilingPoint/C

-252 -196 -34 100

Forces London force

London force

London force

London forceDipole/dipoleHydrogen bonding

--

--

--

H2

London forces N2

London forces CI2

London forces H2OLondon forcesDipole/dipoleHydrogen bond


--

--

---

---

---

- --

Hydrogen bondingHydrogen bonding

RMM lowest - boiling point highest - due to hydrogen bonding

HCI HBr HI HF

RMM 36.5 81 128 20

BoilingPoint/C

-85 -66 -35 19.5

Forces London force/VD

F

London force/VD

F

London force/VDF

Londonforce/VDFDipole/dipoleHydrogen bond


Which liquid has higher boiling point?

H H

H

HH

H

DNA

Br Br

Br

I I

IHydrogen bonding


Hydrogen Bond bet nitrogenous base

HCI HBr HI HF

RMM 36.5 81 128 20

BoilingPoint/C

-85 -66 -35 19.5

Forces London force/VD

F

London force/VD

F

London force/VDF

Londonforce/VDFDipole/dipoleHydrogen bond



H H

H

HH

H

DNA

Br Br

Br

I I

IHydrogen bonding


Br2 ICI

RMM 162 162

B/p/C 58 97

Forces

London force/VDF

London force/VDF

Dipole/dipole


---

---

Br2

London forces bet molecules

Br Br Br Br I I ICI CI CI + + + - - -

ICILondon forces + Dipole –dipole attraction

Hydrogen Bond bet nitrogenous base

CH3CH2OH CH3CH2CH2OH CH3COOH C2H5-O-C2H5

RMM 46 60 60 74

BoilingPoint/C

78 97 118 34

Forces LondonH2 bond

London H2 bond

London H2 bond

London

RMM - London force – boiling point


Stronger Hydrogen bond – boiling point

....

.......

....Hydrogen bond

Hydrogen bond

....✕

C3H8 CH3CHO CH3CH2OH

RMM 44 44 46

BoilingPoint/C

-42 20.2 118

Forces London

London Dipole/dipole


H2 bond


…...

....

…..…

..

.......

..........

…...

London forces London forces + Dipole/dipole

London forces + Dipole/dipole +Hydrogen Bond

Hydrogen bond


RMM 46 60 60 74

BoilingPoint/C

78 97 118 34


London H2 bond

London H2 bond

London




....

.......

....Hydrogen bond

Hydrogen bond

....✕


RMM 44 44 46

BoilingPoint/C

-42 20.2 118

Forces London



H2 bond

RMM highest

No Hydrogen Bond


…...

....

…..…

..

.......

..........

…...



✕

Hydrogen bond


RMM 46 60 60 74

BoilingPoint/C

78 97 118 34


London H2 bond

London H2 bond

London




CH3COOH boiling point higherC=O (carbonyl) – electron withdrawing gp

withdraw electron from OH gp

O-H gp more polarised

stronger H2 bond

....

.......

....Hydrogen bond

Hydrogen bond

....✕

C - O - H

=

o


RMM 44 44 46

BoilingPoint/C

-42 20.2 118

Forces London



H2 bond

RMM highest

No Hydrogen Bond


…...

....

…..…

..

.......

..........

…...



✕

Hydrogen bond

Why 2 Nitrophenol has lower b/p than 4 nitrophenol?

C6H5NO3

( 2 nitrophenol)C6H5NO3

( 4 nitrophenol)

RMM 139 139

BoilingPoint/C

216 279

Forces LondonIntramolecular

H2 bond

London Intermolecular

H2 bond

Which NCI3 is polar but BCI3 non polar?

...

…

Intramolecular H2 bond Non polar

……

✕ Intermolecular H2 bond

✓

✓

BCI3 NCI3

RMM 117 120

BoilingPoint/C

13 71

Forces London London Dipole/dipole

…...

Non polar

... δ-

δ- δ-

δ-+

polar

polar

…..... ✓Dipole dipole

Why 2 Nitrophenol has lower b/p than 4 nitrophenol?

Molecule symmetrical


No net dipole moment

Molecule NON POLAR

C6H5NO3

( 2 nitrophenol)C6H5NO3

( 4 nitrophenol)

RMM 139 139

BoilingPoint/C

216 279

Forces LondonIntramolecular

H2 bond

London Intermolecular

H2 bond

Which NCI3 is polar but BCI3 non polar?

...

…

Intramolecular H2 bond Non polar

……

✕

More intramolecular H2 bond

Lack intermolecular H2 bond

Intermolecular H2 bond

✓

✓

More intermolecular H2 bond

Lack intramolecular H2 bond

BCI3 NCI3

RMM 117 120

BoilingPoint/C

13 71

Forces London London Dipole/dipole

…...

Non polar

... δ-

δ- δ-

δ-+

polar

polar

….....

Molecule asymmetrical

Bond polarity does not cancel

NET dipole moment

Molecule POLAR

✓Dipole dipole

Polarity for Cis/Trans Geometrical Isomers

Cisdichloroethene

Transdichloroethene

RMM 96 96

MeltingPoint/C

-80 -50

Boiling Point/C

60 48

...

δ- Cis

Dipole dipole

Trans

.........

Cisdichloroethene

Transdichloroethene

MeltingPoint/C

-80 -50

Kink/ bend shape

Cisdichloroethene

Transdichloroethene

BoilingPoint/C

60 48

Greater attraction

δ+ δ+

δ-

δ- δ-

......

Cis Trans

Non polar

Non polar

Polar

Polar

Cis Trans

…......

…......

✓ ✓

Trans isomer – CI opposite side


NO Net dipole moment / NON POLAR

Intermolecular forces weaker

Molecule in linear shape

Able to pack closely together

Greater surface area for interaction

Intermolecular forces stronger


Molecule in kink/bend shape

Unable to pack closely together

Less surface area for interaction


Cisdichloroethene

Transdichloroethene

RMM 96 96

MeltingPoint/C

-80 -50

Boiling Point/C

60 48

...

δ- Cis

Dipole dipole

Trans

.........

Cisdichloroethene

Transdichloroethene

MeltingPoint/C

-80 -50

Kink/ bend shape

Cisdichloroethene

Transdichloroethene

BoilingPoint/C

60 48

Greater attraction

Cis isomer – CI same side


Net dipole moment /POLAR


δ+ δ+

δ-

δ- δ-

......

Cis Trans

Non polar

Non polar

Polar

Polar

Cis Trans

…......

…......

✓ ✓

Trans isomer – CI opposite side


NO Net dipole moment / NON POLAR


Molecule in linear shape

Able to pack closely together

Greater surface area for interaction



Molecule in kink/bend shape

Unable to pack closely together

Less surface area for interaction


Cisdichloroethene

Transdichloroethene

RMM 96 96

MeltingPoint/C

-80 -50

Boiling Point/C

60 48

...

δ- Cis

Dipole dipole

Trans

.........

Cisdichloroethene

Transdichloroethene

MeltingPoint/C

-80 -50

Kink/ bend shape

Cisdichloroethene

Transdichloroethene

BoilingPoint/C

60 48

Greater attraction

Cis isomer – CI same side


Net dipole moment /POLAR


δ+ δ+

δ-

δ- δ-

......

Cis Trans

Non polar

Non polar

Polar

Polar

Cis Trans

…......

…......

✓ ✓

RMM increases

Number electron

VDF increases

Evidence for Hydrogen Bonding

Boiling Point group 4 Hydrides

Group 4, 5, 6, 7 HydridesGroup 4 – SiH4, GeH4, SnH4

Group 5 – PH3, AsH3, SbH3

Group 6 – H2S, H2Se, H2TeGroup 7 – HCI, HBr, HI

RMM increases

Number electron

VDF increases

H2O•2 hydrogen atoms•2 lone pairs on oxygen

4 Hydrogen bonding available

Evidence for Hydrogen Bonding

Boiling Point group 4 Hydrides

Group 4, 5, 6, 7 HydridesGroup 4 – SiH4, GeH4, SnH4

Group 5 – PH3, AsH3, SbH3

Group 6 – H2S, H2Se, H2TeGroup 7 – HCI, HBr, HI

High boiling point forNH3, HF, H2O due to hydrogen bonding

H2O HF

HF•1 hydrogen atom•3 lone pairs on fluorine

Lack hydrogen atoms for hydrogen bond

NH3

NH3

•3 hydrogen atoms•1 lone pairs on ammonia

Lack lone pairs for hydrogen bond

CH3-C=O CH3-C-CH3 CH3C-O-H CH3-O-CH3 CH3-N-H CH3-C-N-H I II II I II

H O O H O

Which of the following molecules are polar/non polar?

ICI BCI3 CH2CI2 SF6 NF3 CO2

δ+ δ- δ+ δ-

δ-

δ-

δ+

δ+

δ+ δ+

δ-

δ- δ-

δ-

δ-

δ-

δ-

δ- δ-

δ-

δ-

δ- δ-

Which of the following molecules have hydrogen bonding?

CH3CHO CH3COCH3 CH3COOH CH3OCH3 CH3NH2 CH3CONH2

CH3-C=O CH3-C-CH3 CH3C-O-H CH3-O-CH3 CH3-N-H CH3-C-N-H I II II I II

H O O H O

Which of the following molecules are polar/non polar?

ICI BCI3 CH2CI2 SF6 NF3 CO2

δ+ δ- δ+ δ-

δ-

δ-

δ+

δ+

δ+ δ+

δ-

δ- δ-

δ-

δ-

δ-

δ-

δ- δ-

δ-

δ-

δ- δ-

Polar bond Polar Bond Polar Bond Polar Bond Polar Bond Polar Bond

Bond Polarity Bond Polarity Bond Polarity Bond Polarity Bond Polarity Bond Polarity exist cancel exist cancel exist cancel(Asymmetric) (Symmetrical) (Asymmetrical) (Symmetrical) (Asymmetrical) (Symmetrical)

✓✓✓

Which of the following molecules have hydrogen bonding?

CH3CHO CH3COCH3 CH3COOH CH3OCH3 CH3NH2 CH3CONH2

Hydrogen NOT No Hydrogen Bond Hydrogen attach No Hydrogen Bond Hydrogen attach Hydrogen attach attach to N,O,F to N, O, F to N, O, F to N, O, F

✕ ✕✓ ✓ ✓✕

✕ ✕ ✕

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com

Education

IB Chemistry on Polarity, Hydrogen Bonding and Van Der Waals forces