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

1. 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
Covalent Bonds
Sharing of electron
bet non metal atoms
Equal sharing electrons
+ -electrostatic forces
attraction
4 0.4 0
Difference 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 polarIonic
EN – 3
Diff = (3 – 2.1 ) = 0.9
Na+
CI-
EN – 3

2. 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
H
2.2
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
Bond polarity cancel out each other
Polar bonds – molecule POLAR
Lewis structure
VSEPR
Geometry
1
4 ECC
3 bond pair
1 lone pair
..
N
H
H
H
Polarity
2
3
4
Polar
✓✗

3. ✗
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
Polar covalent Bonds Non Polar covalent Bond
Equal sharing electronUnequal sharing electron
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
+ -
O
III
C δ+
δ-
Turning force – dipole moment
+ -
O
II
C
II
O
δ+
δ-
δ-
No Turning force – No dipole moment
✓
Molecule polar ✓
O
O

4. 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-
Bond polarity
don’t cancel
Bond polarity
cancel
H
Net Dipole moment No Net Dipole moment
✗
Asymmetrical Symmetrical
δ-δ+
Polar bonds
Bond polarity
don’t cancel
Net Dipole moment
C O
Polar bond
Polarity dont cancel
(ASYMMETRICAL)
Net dipole moment
Molecule POLAR
δ- δ-
Polar bonds
Bond polarity cancel
No Net Dipole moment
Polar bond
Polarity cancel
(SYMMETRICAL)
NO dipole moment
Molecule NON POLAR
✗ ✗✓
✓
I

5. 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 forces
Polar 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

6. Permanent dipole
Polar Non Polar
Temporary dipole
(instantaneously induced dipole)
London dispersion forces
Van Der Waals’ Forces attraction
Polar molecule (dipole – dipole attraction)
Polar molecules due to diff in EN values
Dipole/dipole interaction
Electrostatic forces attraction bet molecules
Dipole/dipole attraction Dipole/dipole attraction
Hydrogen bonding (dipole – dipole attraction)
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
Intermolecular force bet molecule (IMF)
Non Polar molecule (Induced dipole attraction)
Random movement /distribution of electron
Instantaneous negative charge on atom
Induced a temporary dipole separation
Electrostatic forces attraction bet molecules
Non polar molecules
Polar molecules
Polar molecules
Forces bet molecule
Molecules

7. Hydrogen bonding (dipole – dipole attraction)
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
Permanent dipole
Polar Non Polar
Temporary dipole
(instantaneously induced dipole)
London dispersion forces
Van Der Waals’ Forces attraction
Polar molecule
Polar molecules due to diff in EN values
Dipole/dipole interaction
Electrostatic forces attraction bet molecules
Dipole/dipole attraction Dipole/dipole attraction
Molecules
Non Polar molecule (Induced dipole attraction)
Random movement /distribution of electron
Instantaneous negative charge on atom
Induced a temporary dipole separation
Instantaneous dipole in one atom
induce a dipole in its neighbor
Electrostatic forces attraction bet molecules
Non polar molecules
Polar molecules
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+

8. 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
Dipole – dipole attraction Induced – dipole attraction
London dispersion forces
Polar Non Polar
All molecules have London dispersion forces due to uneven distribution of electron cloud
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
δ+δ-
London dispersion forces
RMM/Size Surface Area
London dispersion forces
Van Der Waals’ Forces attraction
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
Temporary induced dipole increase
Van Der Waals bet molecules increase
RMM – 72
RMM – 72
Pentane (C5H12)
Factor affecting b/p of molecules
Temporary dipole attraction
London dispersion force
Permanent dipole attraction
Dipole/dipole attraction
Hydrogen bonding

9. Factors affecting VDF forcesFactor affecting b/p of molecules
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
Temporary induced dipole increase
Van Der Waals bet molecules increase
RMM – 72
RMM – 72
Pentane (C5H12)
Temporary dipole attraction
London dispersion force
Permanent dipole attraction
Dipole/dipole attraction
Hydrogen bonding
H2 N2 CI2 H2O
RMM 2 28 71 18
Boiling
Point/C
-252 -196 -34 100
Forces London
force
London
force
London
force
London force
Dipole/dipole
Hydrogen bonding
-
-
--
--
H2
London forces
N2
London forces
CI2
London forces
H2O
London forces
Dipole/dipole
Hydrogen bond
RMM increase  - London force/VDF increase  – boiling point increase 
-
-
-
-
--
-
-
--
-
-
-
-
-
-
Hydrogen bondingHydrogen bonding
RMM lowest  - boiling point highest  - due to hydrogen bonding

10. HCI HBr HI HF
RMM 36.5 81 128 20
Boiling
Point/C
-85 -66 -35 19.5
Forces London
force/VDF
London
force/VDF
London
force/VDF
London
force/VDF
Dipole/dipole
Hydrogen bond
RMM increase  - London force/VDF increase  – boiling point increase 
Which liquid has higher boiling point?
H H
H
H
H
H
DNA
Br Br
Br
I I
I
Hydrogen bonding
RMM lowest  - boiling point highest  - due to hydrogen bonding
Br2 ICI
RMM 162 162
B/p/C 58 97
Forces London
force/VDF
London
force/VDF
Dipole/dipole
Which liquid has higher boiling point?
-
-
-
-
-
-
Br2
London forces bet molecules
Br Br Br Br I I ICI CI CI
+ + +- - -
ICI
London forces + Dipole –dipole attraction
Hydrogen Bond bet
nitrogenous base

11. CH3CH2OH CH3CH2CH2OH CH3COOH C2H5-O-C2H5
RMM 46 60 60 74
Boiling
Point/C
78 97 118 34
Forces London
H2 bond
London
H2 bond
London
H2 bond
London
RMM  - London force  – boiling point 
Which liquid has higher boiling point?
Stronger Hydrogen bond  – boiling point 
CH3COOH boiling point higher
C=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
C3H8 CH3CHO CH3CH2OH
RMM 44 44 46
Boiling
Point/C
-42 20.2 118
Forces London London
Dipole/dipole
London
Dipole/dipole
H2 bond
RMM highest
No Hydrogen Bond
Which liquid has higher boiling point?
.......
..........
London forces London forces
+
Dipole/dipole
London forces
+
Dipole/dipole
+
Hydrogen Bond
✕
Hydrogen
bond

12. Why 2 Nitrophenol has lower b/p than 4 nitrophenol?
Molecule symmetrical
Bond polarity cancel
No net dipole moment
Molecule NON POLAR
C6H5NO3
( 2 nitrophenol)
C6H5NO3
( 4 nitrophenol)
RMM 139 139
Boiling
Point/C
216 279
Forces London
Intramolecular
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
Boiling
Point/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

13. Trans isomer – CI opposite side
Bond polarity cancel
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
Polarity for Cis/Trans Geometrical Isomers
Molecule in kink/bend shape
Unable to pack closely together
Less surface area for interaction
Intermolecular forces weaker
Cis
dichloroethene
Trans
dichloroethene
RMM 96 96
Melting
Point/C
-80 -50
Boiling
Point/C
60 48
...
δ-
Cis
Dipole dipole
Trans
...
...
...
Cis
dichloroethene
Trans
dichloroethene
Melting
Point/C
-80 -50
Kink/ bend shape
Cis
dichloroethene
Trans
dichloroethene
Boiling
Point/C
60 48
Greater attraction
Cis isomer – CI same side
Bond polarity does not cancel
Net dipole moment /POLAR
Intermolecular forces stronger
δ+ δ+
δ-
δ- δ-
...
...
Cis Trans
Non polar
Non polar
Polar
Polar
Cis Trans
…......
…......
✓ ✓

14. 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 Hydrides
Group 4 – SiH4, GeH4, SnH4
Group 5 – PH3, AsH3, SbH3
Group 6 – H2S, H2Se, H2Te
Group 7 – HCI, HBr, HI
High boiling point for
NH3, 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

15. 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 hydrogenbonding?
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
✕ ✕✓ ✓ ✓✕
✕ ✕ ✕