Chemistry Form 6 Chap 03 New

PREPRE--UNIVERSITYUNIVERSITY

SEMESTER 1SEMESTER 1

CHAPTER 3CHAPTER 3

CHEMICAL CHEMICAL

BONDINGBONDING

�� Chemical Bonding can be generally divide to 5 main groupChemical Bonding can be generally divide to 5 main group

�� Electrovalent bonding (ionic)Electrovalent bonding (ionic)

�� Covalent bondingCovalent bonding

�� Metallic bondingMetallic bonding

�� Hydrogen bondingHydrogen bonding

�� Van der Waals bondingVan der Waals bonding

�� To represent the types of bonding, a Lewis diagram (dotTo represent the types of bonding, a Lewis diagram (dot--andand--

cross) is used. Each dot or cross represent one electron in cross) is used. Each dot or cross represent one electron in

valence shell and it’s a more convenient way in showing valence shell and it’s a more convenient way in showing valence shell and it’s a more convenient way in showing valence shell and it’s a more convenient way in showing

electrovalent.electrovalent.

�� For both ionic & covalent bonding, octet rule must be fulfill For both ionic & covalent bonding, octet rule must be fulfill

where tendency of atoms to achieve noble gas configuration. where tendency of atoms to achieve noble gas configuration.

Table 6.2 show some cation/anion with difference number of Table 6.2 show some cation/anion with difference number of

valence electron.valence electron.

Electrovalent bond (ionic bond)Electrovalent bond (ionic bond)

�� Formed by transfering 1 or more eFormed by transfering 1 or more e-- from outer orbital to from outer orbital to another. The atom ‘donate’ electron is name as cation and the another. The atom ‘donate’ electron is name as cation and the atom who ‘receive’ electron is name as anion. The bond form atom who ‘receive’ electron is name as anion. The bond form when electrostatic attraction occur between 2 opposite charge when electrostatic attraction occur between 2 opposite charge ions.ions.

�� Formation of ionic compound involving a metal with low IE and Formation of ionic compound involving a metal with low IE and a nona non--metal with high EA. Example for lithium fluoride (LiF). metal with high EA. Example for lithium fluoride (LiF). The electronic structure of the lithium and fluorine are :The electronic structure of the lithium and fluorine are :

Lithium (Li) = 1sLithium (Li) = 1s22 2s2s11Lithium (Li) = 1sLithium (Li) = 1s22 2s2s11

Fluorine (F) = 1sFluorine (F) = 1s22 2s2s22 2p2p55

�� Practice : Draw the Lewis dot and cross diagram for these ionic Practice : Draw the Lewis dot and cross diagram for these ionic

compoundcompound

Sodium chloride Magnesium fluoride

NaNa

++

ClCl

__

MgMg

2+2+

FF

__

22

NaNa++

ClCl-- MgMg

2+2+FF

--

Aluminium oxide

AlAl

3+3+

22

OO

22--

33

NaNa ClCl MgMg FF22

AlAl3+3+

OO22--

3322

Covalent Bonding : Sharing of ElectronCovalent Bonding : Sharing of Electron

�� Covalent Covalent bond is bond that formed in between atoms by bond is bond that formed in between atoms by

sharing electron from its atoms in order to achieve a stable sharing electron from its atoms in order to achieve a stable

electronic configuration of nselectronic configuration of ns22 npnp66 for atoms involve. (hydrogen for atoms involve. (hydrogen

achieve 1sachieve 1s22))

�� Some nonSome non--metallic elements exist naturally as diatomic metallic elements exist naturally as diatomic

molecules like hydrogen, and halogens groupsmolecules like hydrogen, and halogens groups..

Hydrogen molecule Chlorine molecule Oxygen molecule Nitrogen molecule

�� From example above, we can see that in covalent bond, From example above, we can see that in covalent bond,

molecules may form single bond, double bond or triple bond in molecules may form single bond, double bond or triple bond in

order to achieve stable valence electrons. Though, there are order to achieve stable valence electrons. Though, there are

some molecules with the exceptions of achieving stable some molecules with the exceptions of achieving stable

valence electrons.valence electrons.

�� Electron deficient compounds Electron deficient compounds –– compounds which the molecule compounds which the molecule

(especially the (especially the centercenter atom) does not achieve octet electron atom) does not achieve octet electron

arrangement. Examples of these molecules are BeClarrangement. Examples of these molecules are BeCl22 ; BF; BF33 and and

AlClAlCl33..

Beryllium dichloride Boron trifluoride Aluminium trichloride

Cl Be ClCl Be Cl

�� Electron rich compounds Electron rich compounds –– compounds which have more than 8 compounds which have more than 8

electrons at center atom of molecules, such as PClelectrons at center atom of molecules, such as PCl55, SF, SF66 and ICland ICl55..

Phosphorous pentachloride Sulphur hexachloride Iodine pentachloride

�� However, not all compounds can have more or less than 8 electrons However, not all compounds can have more or less than 8 electrons

in the in the centercenter of the atom. There are certain limitation towards the of the atom. There are certain limitation towards the

application of the expansion of application of the expansion of centercenter atomatom

�� For example, nitrogen (N) and phosphorous (P) are both from For example, nitrogen (N) and phosphorous (P) are both from

Group @@@ but phosphorous can exist as PClGroup @@@ but phosphorous can exist as PCl33 and PCland PCl55 while while

nitrogen can only have NClnitrogen can only have NCl33 but not NClbut not NCl55. This is because . This is because

@@@@.....................@@@@.....................@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

@@@@@@@@@@@@@@@@@@@@..................................@@@@@@@@@@@@@@@@@@@@..................................

�� Same things occur when it come to Same things occur when it come to hydrolysis of CClhydrolysis of CCl44 and SiCland SiCl44. .

SiClSiCl can undergoes hydrolysis with water according to the equationcan undergoes hydrolysis with water according to the equation

1515

nitrogen which only have 2 shell, do not have empty dnitrogen which only have 2 shell, do not have empty d--orbital orbital

available, but phosphorous contain davailable, but phosphorous contain d--orbital to fill in more electronorbital to fill in more electron

SiClSiCl44 can undergoes hydrolysis with water according to the equationcan undergoes hydrolysis with water according to the equation

@@@@@@@@@@@@@@@@@@@@@@@@@@.@@@@@@@@@@@@@@@@@@@@@@@@@@.

while CClwhile CCl4 4 cannot. Despite the factors that they are from the same cannot. Despite the factors that they are from the same

group (Group @@@), CClgroup (Group @@@), CCl44 cannot undergoes hydrolysis as cannot undergoes hydrolysis as

@@@@@@@@@@@@@@@@@@@@...@@@@@@@@@@@@@@@@@@@@@@@@@@@@@...@@@@@@@@@

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

SiClSiCl4 4 + 2 H+ 2 H22O O �� SiOSiO22 + 4 HCl+ 4 HCl

1414

carbon which only have 2 shell, do not have empty dcarbon which only have 2 shell, do not have empty d--orbital orbital

available, so water cannot form coordinative with carbon hence available, so water cannot form coordinative with carbon hence

cannot undergoes hydrolysis.cannot undergoes hydrolysis.

�� Examples : Draw the Lewis structure for the following molecules.Examples : Draw the Lewis structure for the following molecules.

CO2 HCN CH3COOH

C2H2 NH3 CO32-

SO42- C3H6

�� 6.2.16.2.1 Dative bondDative bond

�� Now, try drawing the Lewis structure for these molecules : SONow, try drawing the Lewis structure for these molecules : SO22, ,

SOSO33, NO, NO33-- or CO.or CO.

SO2 SO3 NO3- CO

�� Dative bond is formed when Dative bond is formed when an atom that has lone pair an atom that has lone pair

electrons which can donate to molecule/ion that has empty electrons which can donate to molecule/ion that has empty

unhybridiseunhybridise orbital. orbital.

�� Following are a few applications of dative bond in covalent Following are a few applications of dative bond in covalent

moleculesmolecules

1.1. Dative bond in helping molecule to achieve octet.Dative bond in helping molecule to achieve octet.

NH4+ BF3.NH3

�� Dative bond in forming Dative bond in forming dimerdimer ~ 2 monomer combine forming a ~ 2 monomer combine forming a

dimerdimer..

Forming Al2Cl6 Forming polymer of BeCl2

Cl

Be

Cl

Cl

Be

Cl

Cl

Be

Cl

Cl Cl

3.3. Dative bond in formation of complex ion.Dative bond in formation of complex ion.

�� Molecule / ion form dative bond (also known as coordinative bond) Molecule / ion form dative bond (also known as coordinative bond)

by donating lone pair electron, which act as a @@@@.. in the by donating lone pair electron, which act as a @@@@.. in the

formation of complex ions. For exampleformation of complex ions. For example

hexaaquacopper (II) ion ;

[Cu(H2O)6]2+

tetraamminenickel (II) ion ;

[Ni(NH3)42+]

Hexacyanoferrate (III) ion ;

[Fe(CN)6]3-

ligandligand

6.2.36.2.3 Resonance ~ Resonance ~ a molecule/polyatomic ion in which two or more a molecule/polyatomic ion in which two or more

plausible Lewis structure can be written but the actual structure plausible Lewis structure can be written but the actual structure

cannot be written at allcannot be written at all

Sulphur dioxide, SO2

Ethanoate ion, CH3COO–

Nitrogen dioxide, NO2

Sulphur trioxide, SO3

Carbonate ion, CO32-

O 2-O

2-O

2-

CO O

C

OOC

OO

�� Since the resonance structure cannot be determined as it does not Since the resonance structure cannot be determined as it does not

have a permanent structure so it is expressed as a combined of have a permanent structure so it is expressed as a combined of

resonance structure known as resonance structure known as resonance hybridresonance hybrid

�� Resonance hybridResonance hybrid

CO

O

O

2-

Covalent Bonds : Overlapping of OrbitalsCovalent Bonds : Overlapping of Orbitals

�� 2 ways in explaining how covalent bond are attached :2 ways in explaining how covalent bond are attached :

�� Valence bond theoryValence bond theory

�� ValenceValence--shell electronshell electron--pair repulsion theory (VSEPR)pair repulsion theory (VSEPR)

�� Here we can explain and predict what type of molecular bond Here we can explain and predict what type of molecular bond

and shape will form through the bonding formation but it does and shape will form through the bonding formation but it does

not explain the stability of covalent bond.not explain the stability of covalent bond.

�� For valence bond theory, it used atomic orbital overlapping For valence bond theory, it used atomic orbital overlapping �� For valence bond theory, it used atomic orbital overlapping For valence bond theory, it used atomic orbital overlapping

that result the formation of a new molecular orbital embracing that result the formation of a new molecular orbital embracing

both nuclei. The strength of covalent bond is proportional to both nuclei. The strength of covalent bond is proportional to

the area where the atomic orbital overlap. Larger the area the area where the atomic orbital overlap. Larger the area

overlap, stronger the covalent bond.overlap, stronger the covalent bond.

Hybrid Atomic Hybrid Atomic OrbitalsOrbitals

�� 3 basic types of hybrid orbital3 basic types of hybrid orbital

�� spsp33 hybrid orbital (tetrahedral arrangement)hybrid orbital (tetrahedral arrangement)

�� spsp22 hybrid orbital (hybrid orbital (trigonaltrigonal planar arrangement)planar arrangement)

�� sp hybrid orbital (linear arrangement) sp hybrid orbital (linear arrangement)

6.3.26.3.2 spsp33 hybridisationhybridisation

�� The term spThe term sp33 gives an impression of the hybridisation involved gives an impression of the hybridisation involved

_____ s orbital and _____ p _____ s orbital and _____ p orbitalsorbitals

�� Examples of molecules which give spExamples of molecules which give sp33 hybridisation arehybridisation are

�� For example, in methane, CHFor example, in methane, CH , since carbon is in Group _____so , since carbon is in Group _____so

Methane silicon tetrachloride

sulphate ion Perchlorate ion

11 33

CHCH44 SiClSiCl44

SOSO4422-- ClOClO44

--

1414�� For example, in methane, CHFor example, in methane, CH44, since carbon is in Group _____so , since carbon is in Group _____so

the valance electron of C is _______the valance electron of C is _______

14142s2s22 2p2p22

State of

moleculesOrbital diagram Illustration / Explanation

Ground

state

_____ _____ _____

2p

____

2s

Excited

state____ ____ ____ ____

2s 2p

Hybridisati

on state

_____ _____ _____ _____

sp3

109.5109.500

tetrahedraltetrahedral

6.3.36.3.3 spsp22 hybridisationhybridisation

�� The term spThe term sp22 gives an impression of the hybridisation involved gives an impression of the hybridisation involved

_____ s orbital and _____ p _____ s orbital and _____ p orbitalsorbitals

�� Examples of molecules which give spExamples of molecules which give sp22 hybridisation arehybridisation are

�� Since boron is Group ______ element so the electron valance Since boron is Group ______ element so the electron valance

Sulphur trioxide Boron trifluoride

Nitrate ion Carbonate ion

11 22

SOSO33 BFBF33

NONO33-- COCO33

22--

13132s2s22 2p2p11of B is _________of B is _________2s2s22 2p2p11

State of

moleculesOrbital diagram Illustration / Explanation

Ground

state

_____ _____ _____

2p

____

2s

Excited

state

____ ____ ____ ____

2s 2p

Hybridisati

on state

_____ _____ _____ ____

sp2 pz

Formation of sp2 Hybrid Orbitals

Shape of molecule Shape of molecule

TrigonalTrigonal planarplanar

Angle between Angle between

bond pair bond pair

120120oo

6.3.46.3.4 sp hybridisationsp hybridisation

�� The term sp gives an impression of the hybridisation involved The term sp gives an impression of the hybridisation involved

_____ s orbital and _____ p _____ s orbital and _____ p orbitalsorbitals

�� Examples of molecules which give sp hybridisation areExamples of molecules which give sp hybridisation are

Carbon dioxide Beryllium chloride

Cyanic acid Ethyne

11 11

COCO22BeClBeCl22

HCNHCN CC22HH22

�� Let’s use beryllium chloride as example. Let’s use beryllium chloride as example.

�� Since beryllium is Group ______ element so the electron Since beryllium is Group ______ element so the electron

valance of Be is ___________valance of Be is ___________

22

2s2s22

State of

moleculesOrbital diagram Illustration / Explanation

Ground

state

_____ _____ _____

2p

____

2s

Excited

state

____ ____ ____ ____

2s 2p

Hybridisati

on state

_____ _____ ___ ___

sp py pz

Formation of sp Hybrid Orbitals

Shape of molecule Shape of molecule

LinearLinear

Angle between bond pair Angle between bond pair

180180oo

6.46.4 Hybridisation in organic moleculesHybridisation in organic molecules

�� In this subtopic, we’re going to witness how is the formation of the In this subtopic, we’re going to witness how is the formation of the

bonding that exist in some organic molecules. The 3 organic bonding that exist in some organic molecules. The 3 organic

molecules which will be discussed in this submolecules which will be discussed in this sub--topic are :topic are :

�� methane, CHmethane, CH44 �� etheneethene, C, C22HH44

�� ethyneethyne, C, C22HH22

�� All of the molecules above has carbon in itAll of the molecules above has carbon in it

�� Carbon is a group _____ element. It has the electronic configuration Carbon is a group _____ element. It has the electronic configuration

of ______________of ______________

1414

2s2s22 2p2p22of ______________of ______________

The orbital diagram The orbital diagram

�� Ground state of carbon : _____Ground state of carbon : _____ _____ _____ __________ _____ _____

2s2s 2p2p

2s2s 2p2p

�� Methane, CHMethane, CH44 Type of hybridisation : Type of hybridisation :

Excited state of carbon : Excited state of carbon : _____ _____ _____ _____ __________ _____ _____

2s2s 2p2p

Hybridised stateHybridised state :: _____ _____ _____ __________ _____ _____ _____

spsp33

Molecular shapeMolecular shape ::

@@@@@@@@@@@@@@@@@@@@@@@@@@tetrahedraltetrahedral@@@@@@@@@@@@@@@@@@@@@@@@@@

Angle between the bonding pair :Angle between the bonding pair :

@@@@@@@@@..@@@@@@@@@..109.5109.500

tetrahedraltetrahedral

EtheneEthene, C, C22HH44 Type of Type of hybridisationhybridisation : :

�� Excited state of C : _____ Excited state of C : _____ _____ _____ __________ _____ _____

2s2s 2p2p

�� HybridisedHybridised statestate : _____ _____ _____ _____: _____ _____ _____ _____

spsp22 ppzz

Molecular shapeMolecular shape

spsp22

Molecular shapeMolecular shape

Angle between bondAngle between bond

pair pair –– bond pairbond pair

TrigonalTrigonal planarplanar

��120120oo

EthyneEthyne, C, C22HH22 Type of Type of hybridisationhybridisation : :

�� Excited state of C : _____ Excited state of C : _____ _____ _____ __________ _____ _____

2s2s 2p2p

�� HybridisedHybridised statestate : _____ _____ : _____ _____ _____ __________ _____

spsp ppyy ppzz

Molecular shapeMolecular shape

spsp

LinearLinear

Angle between bondAngle between bond

pair pair –– bond pairbond pair

180180oo

�� As a conclusion, the formation of double As a conclusion, the formation of double

bond (C=C) is due to ______bond (C=C) is due to ______sigmasigma bond bond

((σσ) and _____) and _____pipi bond (bond (ππ))

�� While the formation of triple bond (C≡C) is While the formation of triple bond (C≡C) is

oneone

oneone

�� While the formation of triple bond (C≡C) is While the formation of triple bond (C≡C) is

due to ______due to ______sigmasigma bond (bond (σσ) and _____) and _____pipi

bond (bond (ππ))

oneone twotwo

�� The Hybridisation of s and p orbitals in Carbon atomThe Hybridisation of s and p orbitals in Carbon atom

�� We’ve discussed methane molecule by using sp3 hybrid We’ve discussed methane molecule by using sp3 hybrid

orbitals in forming the Corbitals in forming the C––H bond in methaneH bond in methane

�� Ethene molecules, CEthene molecules, C22HH44 –– a planar molecule with a bond a planar molecule with a bond

angle of 120angle of 120oo, it can be explain below :, it can be explain below :

�� Formation of Formation of σσ bonds using sp2 hybrid orbitals ~ Since 2 of the bonds using sp2 hybrid orbitals ~ Since 2 of the

bond is use to overlap the bonding between Cbond is use to overlap the bonding between C––H, the third spH, the third sp22

orbital is use to overlap between Corbital is use to overlap between C––C bond. This type of bond is C bond. This type of bond is

what we name as sigma, what we name as sigma, σσ bonds.bonds.what we name as sigma, what we name as sigma, σσ bonds.bonds.

�� Formation of Formation of ππ bonds using pbonds using pzz orbital ~ the p orbital which remain orbital ~ the p orbital which remain

unhybridises (adjacent carbon atom) undergo sideways unhybridises (adjacent carbon atom) undergo sideways

overlapping to form a overlapping to form a ππ bond. In a bond. In a ππ bond, electron cloud is bond, electron cloud is

located above and below the Clocated above and below the C––C bond. Thus, the double bond C bond. Thus, the double bond

in ethene consist in ethene consist σσ and and ππ bonds.bonds.

10.5

10.5

�� Ethyne Molecules CEthyne Molecules C22HH22 (Acetylene)(Acetylene)

�� A linear molecule containing triple bond HA linear molecule containing triple bond H––CC≡C≡C––H. The H. The

bonding in ethyne can be explained as follows.bonding in ethyne can be explained as follows.

�� Formation of Formation of σσ bond using sp hybrid orbital ~ as explain earlier, bond using sp hybrid orbital ~ as explain earlier,

σσ bond is formed when the remain sp orbital is overlapping with bond is formed when the remain sp orbital is overlapping with

each other.each other.

�� Formation of Formation of ππ bonds using pbonds using pyy and pand pzz orbital ~ each carbon orbital ~ each carbon

atom still has 2 unhybridised 2p orbitals oriented at right angles atom still has 2 unhybridised 2p orbitals oriented at right angles

to each other and to the axis of the sp hybrid orbitals. These p to each other and to the axis of the sp hybrid orbitals. These p to each other and to the axis of the sp hybrid orbitals. These p to each other and to the axis of the sp hybrid orbitals. These p

orbital undergo sideways overlapping to form a pair of orbital undergo sideways overlapping to form a pair of ππ bonds. bonds.

Thus, the triple bond in ethyne consists of a Thus, the triple bond in ethyne consists of a σσ bond and two bond and two ππ

bonds.bonds.

10.5

�� The Hybridisation of s and p orbitals in the Oxygen atomThe Hybridisation of s and p orbitals in the Oxygen atom

�� When we sketch the orbital diagram, we should notice that When we sketch the orbital diagram, we should notice that

there’s 2 more space for ethere’s 2 more space for e-- to fill into the p orbital. In the to fill into the p orbital. In the

bond form within water, Hbond form within water, H22O, we found that it has O, we found that it has

geometrical structure nearly similar to a tetrahedral, but the geometrical structure nearly similar to a tetrahedral, but the

angle between 2 Oangle between 2 O––H bond is 104.5H bond is 104.5oo instead of 109.5instead of 109.5oo as in as in

tetrahedral. Here, we can use bonding pair and lone pair tetrahedral. Here, we can use bonding pair and lone pair

repulsion theory to explain the situation.repulsion theory to explain the situation.

Ground StateGround State Hybridised StateHybridised State

�� Hybridisation of s and p orbital in Nitrogen AtomHybridisation of s and p orbital in Nitrogen Atom

�� Same as oxygen case, nitrogen also uses a sp3 hybrid orbital Same as oxygen case, nitrogen also uses a sp3 hybrid orbital

for forming covalent bond between N and 3 H atoms. One of for forming covalent bond between N and 3 H atoms. One of

the lone pair electron occupied the orbital and this will cause the lone pair electron occupied the orbital and this will cause

repulsion of bonding to occur that makes the angle of the repulsion of bonding to occur that makes the angle of the

bond become 107bond become 107oo instead of 109.5instead of 109.5oo. The shape of molecule . The shape of molecule

is pyramidal where 3 H form the base of pyramidis pyramidal where 3 H form the base of pyramid

Ground StateGround State Hybridised StateHybridised State

�� From the 2 examples above, we can tell how the lone pair From the 2 examples above, we can tell how the lone pair

electrons affecting the angle between the bonding pair and electrons affecting the angle between the bonding pair and

bonding pair. In ammonia, not only that there is the repulsion bonding pair. In ammonia, not only that there is the repulsion

between between bonding pair and bonding pairbonding pair and bonding pair but there’s also the but there’s also the

repulsion between repulsion between bonding pair and lone pair.bonding pair and lone pair.

�� Since the angle between the bonding pair and bonding pair Since the angle between the bonding pair and bonding pair

decrease, there’s a probability that its due to the effect of decrease, there’s a probability that its due to the effect of

stronger repulsion between the bonding pair and lone pair stronger repulsion between the bonding pair and lone pair

electron. This statement is supported as in the repulsion electron. This statement is supported as in the repulsion electron. This statement is supported as in the repulsion electron. This statement is supported as in the repulsion

between the Hbetween the H––OO––H in water is smaller than in ammonia, H in water is smaller than in ammonia,

NHNH33. as a conclusion, we can conclude that. as a conclusion, we can conclude that

bonding-pair vs. bonding

pair repulsion

lone-pair vs. lone pair

repulsion

lone-pair vs. bonding

pair repulsion> >

Valence Shell Electron Pair Repulsion (VSEPR) TheoryValence Shell Electron Pair Repulsion (VSEPR) Theory

�� ~ state that the electron~ state that the electron--pair repulsion stated that electron pair repulsion stated that electron

pairs around central atom repel each otherpairs around central atom repel each other

�� 3 main rules3 main rules

�� Bonding pairs and lone pairs of electrons arrange themselves to be Bonding pairs and lone pairs of electrons arrange themselves to be

as far apart as possible.as far apart as possible.

�� The order of repulsion strength of lone pair and bond pair are The order of repulsion strength of lone pair and bond pair are

lonelone--pair & lonepair & lone--pair > lonepair > lone--pair & bondpair & bond--pair > bondpair > bond--pair & bondpair & bond--pairpair

�� Double / triple bond are considered as 1 bonding pair when predicting Double / triple bond are considered as 1 bonding pair when predicting �� Double / triple bond are considered as 1 bonding pair when predicting Double / triple bond are considered as 1 bonding pair when predicting

the shape of molecules or ionsthe shape of molecules or ions

�� Diagram below shows the type of bonding and the molecular Diagram below shows the type of bonding and the molecular

shape predicted.shape predicted.

AB2 2 0 linear linear

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB3 3 0trigonal

planar

trigonal

planar

AB4 4 0 tetrahedral tetrahedral

AB5 5 0trigonal

bipyramidal

trigonal

bipyramidal

AB6 6 0 octahedraloctahedral

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB3 3 0trigonal

planar

trigonal

planar

AB2E 2 1trigonal

planarbent

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB3E 3 1

AB4 4 0 tetrahedral tetrahedral

tetrahedraltrigonal

pyramidal

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB4 4 0 tetrahedral tetrahedral

AB3E 3 1 tetrahedraltrigonal

pyramidal

AB2E2 2 2 tetrahedral bent

H

O

H

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB5 5 0trigonal

bipyramidal

trigonal

bipyramidal

AB4E 4 1trigonal

bipyramidalSee-saw

bipyramidal

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB5 5 0trigonal

bipyramidal

trigonal

bipyramidal

AB4E 4 1trigonal

bipyramidal

distorted

tetrahedron

10.1

bipyramidal tetrahedron

AB3E2 3 2trigonal

bipyramidalT-shaped

ClF

F

F

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB5 5 0trigonal

bipyramidal

trigonal

bipyramidal

AB4E 4 1trigonal

bipyramidal

distorted

tetrahedronbipyramidal tetrahedron

AB3E2 3 2trigonal

bipyramidalT-shaped

AB2E3 2 3trigonal

bipyramidallinear

I

I

I

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB6 6 0 octahedraloctahedral

AB5E 5 1 octahedralsquare

pyramidal

F

Br

F F

FF

F

Class

# of atoms

bonded to

central atom

# lone

pairs on

central atom

Arrangement of

electron pairs

Molecular

Geometry

VSEPR

AB6 6 0 octahedraloctahedral

AB5E 5 1 octahedralsquare

pyramidal

square AB4E2 4 2 octahedral

square

planar

Xe

F F

FF

�� 5 GENERAL STEPS TAKEN WHEN WRITING LEWIS 5 GENERAL STEPS TAKEN WHEN WRITING LEWIS

STRUCTURE FOR MOLECULES AND IONSSTRUCTURE FOR MOLECULES AND IONS

�� Calculate the total number of valence electrons from all atomsCalculate the total number of valence electrons from all atoms

�� Arrange all the atoms surrounding the central atom by using a Arrange all the atoms surrounding the central atom by using a

pair of electron per bondpair of electron per bond

�� Assign the remaining electrons to the terminal atoms so that Assign the remaining electrons to the terminal atoms so that

each terminal atom has 8 electrons (H = 2 eeach terminal atom has 8 electrons (H = 2 e--))

�� Place any leftPlace any left--over electron on the central atom.over electron on the central atom.

@@ Form Form multiple bonds if there are not enough electrons to give the multiple bonds if there are not enough electrons to give the @@ Form Form multiple bonds if there are not enough electrons to give the multiple bonds if there are not enough electrons to give the

central atom an octet of electrons.central atom an octet of electrons.

6.66.6 ElectronegativityElectronegativity and Polar Moleculesand Polar Molecules

�� ElectronegativityElectronegativity are measurement of ability of an atom in are measurement of ability of an atom in

molecules to attract a pair of electronmolecules to attract a pair of electron

�� For 2 identical atoms, since they have same For 2 identical atoms, since they have same electronegativityelectronegativity so so

they have no difference in they have no difference in electronegativityelectronegativity. These molecules are . These molecules are

called called polar moleculespolar molecules

�� While if 2 not identical form a covalent bond, the bonding electrons While if 2 not identical form a covalent bond, the bonding electrons

will attracted more strongly by more will attracted more strongly by more electronegative element.electronegative element. We We

can indicate the polarity of hydrogen chloride molecules in 2 ways.can indicate the polarity of hydrogen chloride molecules in 2 ways.

HH ClCl�� The separation of charge (between The separation of charge (between δδ+ and + and δδ–– ) in a poplar ) in a poplar

molecule is called molecule is called dipoledipole

�� When 2 electrical charges of opposite sign are separated by small When 2 electrical charges of opposite sign are separated by small

distance, distance, dipole momentdipole moment is establishedis established

δδ+ + δδ––

�� Molecules that are Molecules that are polarpolar have large dipole moments. have large dipole moments.

�� Molecules that are non polar have Molecules that are non polar have zerozero dipole moment.dipole moment.

�� Still, for some molecules, even there are different in Still, for some molecules, even there are different in

electronegativityelectronegativity but it doesn’t mean that these molecules there but it doesn’t mean that these molecules there

are polar molecules. When the surrounding atom are are polar molecules. When the surrounding atom are

symmetrically surrounded by identical (same) atom, they are symmetrically surrounded by identical (same) atom, they are

nonnon--polarpolar

�� Example of molecules which are non polarExample of molecules which are non polar

Dipole Moments and Polar Molecules

H F

electron rich

regionelectron poor

region

δ+ δ−

µ = Q x r

Q is the charge

r is the distance between charges

1 D = 3.36 x 10-30 C m

Which of the following molecules have a dipole moment?

H2O, CO2, SO2, and CH4

O

dipole moment

polar molecule

S

dipole moment

polar molecule

CO O

no dipole moment

nonpolar molecule

C

H

H

HH

no dipole moment

nonpolar molecule

Nitrogen dioxide, NO2 Methane, CH4 Ethene, C2H4 Benzene, C6H6

Boron trifluoride, BF3 Cyanide acid, HCN Sulphur dioxide, SO2 Sulphur trioxide, SO3

Ammonia, NH3 Ammonium ion, NH4+ Ethane, C2H6 Chloroethane, C2H5Cl

NH

HH

Cyclohexane, C6H12 Chlorocyclohexane,

C6H11Cl

Carbon dioxide, CO2 Carbonate ion, CO32-

CO

O

O

2-

Phosphorous

trichloride, PCl3

Phosphorous

pentachloride, PCl5

cis–but-2-ene trans–but-2-ene

C

H3C

H

C

H

CH3

�� A simple experiment which can A simple experiment which can

be used to determine either a be used to determine either a

molecule is polar or non polar molecule is polar or non polar

is illustrated belowis illustrated below

�� By using the liquid form of the By using the liquid form of the

compound, it is flow out slowly compound, it is flow out slowly

from burette while a negative from burette while a negative

charged rod is bring close to charged rod is bring close to

the flow of the liquid. the flow of the liquid.

�� If the liquid is deflected to the If the liquid is deflected to the �� If the liquid is deflected to the If the liquid is deflected to the

direction of negative charged, direction of negative charged,

this liquid is @@@@this liquid is @@@@

�� If it remain If it remain undeflectedundeflected, this , this

liquid is @@@@@.liquid is @@@@@.

polarpolar

nonnon--polarpolar

�� From the example above, classified which compounds can be From the example above, classified which compounds can be

deflected and which cannotdeflected and which cannot

Compound which can be deflected

by charged rod

Compound which cannot be

deflected by charged rod

Nitrogen dioxide,Nitrogen dioxide,

Cyanide acid,Cyanide acid,

Sulphur dioxide,Sulphur dioxide,

Ammonia,Ammonia,

Methane, Methane, etheneethene, benzene,, benzene,

Sulphur trioxide,Sulphur trioxide,

Ammonium ion,Ammonium ion,

Ethane, Ethane, cyclohexanecyclohexane,,Ammonia,Ammonia,

ChloroethaneChloroethane,,

ChlorocyclohexaneChlorocyclohexane,,

Phosphorous Phosphorous trichloridetrichloride

CisCis--butbut--22--eneene

Ethane, Ethane, cyclohexanecyclohexane,,

Carbon dioxide,Carbon dioxide,

Carbonate ion,Carbonate ion,

Phosphorous Phosphorous pentachloridepentachloride,,

TransTrans--butbut--22--eneene

Electronegativity and Type of Chemical Bond.Electronegativity and Type of Chemical Bond.

�� Actually, the type of bond that would form can be tell by using Actually, the type of bond that would form can be tell by using

the difference of electronegativity (the difference of electronegativity (∆∆EN). More larger the EN). More larger the

difference, the more tendency of electron form low EN move difference, the more tendency of electron form low EN move

an electron to higher EN atom and ionic compound is formed.an electron to higher EN atom and ionic compound is formed.

�� The relationship between the ionic character and the The relationship between the ionic character and the

difference in the electronegativity of the bonded atom is difference in the electronegativity of the bonded atom is

shown on next slide (or page 220).shown on next slide (or page 220).

The presence of dipoles gives ionic character to polar The presence of dipoles gives ionic character to polar �� The presence of dipoles gives ionic character to polar The presence of dipoles gives ionic character to polar

covalent molecules. When the polarity of the covalent covalent molecules. When the polarity of the covalent

molecule increases, the ionic character also increase.molecule increases, the ionic character also increase.

�� An ionic bond is formed if An ionic bond is formed if –– the cation has a small ionic the cation has a small ionic

radius radius –– anion has a large ionic radius anion has a large ionic radius –– both cation & anion both cation & anion

carries a low electrical charge.carries a low electrical charge.

�� Polarisation ~ the distortion of the charge cloud of the Polarisation ~ the distortion of the charge cloud of the

negative ion by a neighbouring positive ion.negative ion by a neighbouring positive ion.

Fig. 9.18Fig. 9.18

3.6.13.6.1 CovalencyCovalency Properties in Ionic MoleculesProperties in Ionic Molecules

�� From the graph above, the dotted line represent the From the graph above, the dotted line represent the

arbitrary line between ionic and covalent characteristic of arbitrary line between ionic and covalent characteristic of

a molecule. To be more specific, there more likely an a molecule. To be more specific, there more likely an

ionic compound may have high covalent characteristic ionic compound may have high covalent characteristic

(exemplified by (exemplified by LiILiI), or conversely covalent compound ), or conversely covalent compound

having high ionic characteristic (exemplified by HF).having high ionic characteristic (exemplified by HF).

�� The covalent characteristic of a molecule is dependent The covalent characteristic of a molecule is dependent

on the ability of a on the ability of a cationcation to to polarisepolarise an anion. an anion. PolarisationPolarisationon the ability of a on the ability of a cationcation to to polarisepolarise an anion. an anion. PolarisationPolarisation

indicates the ability of a indicates the ability of a cationcation to attract the electron to attract the electron

density of an anion when put next to the density of an anion when put next to the cationcation involved. involved.

When a When a cationcation is able to pull the electron density of the is able to pull the electron density of the

anion closer to it, as if the anion wanted to share electron anion closer to it, as if the anion wanted to share electron

with with cationcation, hence increase the , hence increase the covalencycovalency of the of the

moleculemolecule

A+

X– B+ Y–

Highly ionic compoundHighly ionic compound

Large cationic sizeLarge cationic size

Highly covalent compoundHighly covalent compound

small cationic sizesmall cationic size�� Large cationic sizeLarge cationic size

�� Small anionic sizeSmall anionic size

�� small cationic sizesmall cationic size

�� large anionic sizelarge anionic size

• The covalency properties of a molecule is dependent on the

cation and anion where they can be explained qualitatively via

• Polarisation power of cation

• Polarisability of anion

3.6.1.13.6.1.1 PolarisationPolarisation Power of Power of CationCation

�� PolarisationPolarisation Power of Power of CationCation –– measure the ability of a measure the ability of a cationcation

to to polarisepolarise the electron cloud of the anion.the electron cloud of the anion.

�� 2 factors determining the 2 factors determining the polarisationpolarisation power of power of cationcation

Charge of cation Size of cation

⇒ Greater the charge of ion, higher the

effective nuclear charge of cation,

hence it will be able to attract the

neighboring electron density of anion.

⇒ Smaller the size of cation, closer the

neighboring anion to the nucleus of

cation, hence easier for the cation to

polarise the anion and result an neighboring electron density of anion.

This will caused the polarization power

of cation increase, hence increase the

covalent characteristic of cation.

polarise the anion and result an

increment in the polarization power of

cation, and increase the covalent

characteristic of cation.

♦ Both factors can be explained in another term called as charge density where

Charge Density = Charge / Ionic Radius

♦ From the equation above, Charge Density will have a greater value, provided that

cation has a high charge and small cationic radius.

♦ Greater the charge density, higher the polarization power, greater the covalent

characteristic of the cation.

3.6.1.23.6.1.2 PolarisabilityPolarisability of Anionof Anion

�� PolarisabilityPolarisability of an anion ~ ability of the anion to allow the electron of an anion ~ ability of the anion to allow the electron

density to be density to be polarisedpolarised by by cationcation..

�� 2 factors determining the 2 factors determining the polarisabilitypolarisability of an anionof an anion

Charge of anion Size of anion

⇒ Greater the charge of anion, lower the

effective nuclear charge of anion. This will

weakened the electrostatic attraction forces

between nucleus and the outermost

⇒ Larger the size of anion, further the

outermost electron from the nucleus

of the anion, easier for the cation to

polarise the anion, and cause the

�� Unlike Unlike cationcation, anion does not have a term that combined both , anion does not have a term that combined both

factors of charge and ionic radius. However, information of factors of charge and ionic radius. However, information of

polarisabilitypolarisability of anion enable the prediction of the covalent of anion enable the prediction of the covalent

characteristic of a molecule, since in order to form a covalent bond, characteristic of a molecule, since in order to form a covalent bond,

it depend on both it depend on both polarisationpolarisation power of power of cationcation and and polarisabilitypolarisability of of

the anionthe anion

between nucleus and the outermost

electron in anion, and increase the

polarisability of the anion, hence increase

the covalent characteristic of anion

polarise the anion, and cause the

polarisability to increase, hence

increase the covalent characteristic

of anion.

3.6.23.6.2 Prediction of Chemical Bond :Prediction of Chemical Bond :FajansFajans’ Rule’ Rule

�� In 1923In 1923, , KazimierzKazimierz FajansFajans formulated an easy guidance to predict formulated an easy guidance to predict

whether a chemical bond will be covalent or ionic, and depend on whether a chemical bond will be covalent or ionic, and depend on

the charge on the the charge on the cationcation and the relative sizes of the and the relative sizes of the cationcation and and

anion. They can be summarized in the following tableanion. They can be summarized in the following table

Ionic compound Low positive charge Large cation Small anion

Covalent compound High positive charge Small cation Large anion

�� Based on these guidance, the bonding of a few compounds Based on these guidance, the bonding of a few compounds

shall be discussed to understand the application of shall be discussed to understand the application of FajansFajans’ ’

Rule in the chemical bondingRule in the chemical bonding

Lithium halide (Lithium halide (LiXLiX))

�� Lithium ion, LiLithium ion, Li++ (1s(1s22) has a small size due to only 1 shell ) has a small size due to only 1 shell

present in its ion. But since it has a low charge, so its charge present in its ion. But since it has a low charge, so its charge

density is not too high. That is why, all lithium halide are ionic density is not too high. That is why, all lithium halide are ionic

compound. The compound. The covalencycovalency of lithium halide varies from a of lithium halide varies from a

highly highly ioniccharacteristicioniccharacteristic to highly to highly covalencycovalency, depending on , depending on

the the polarisabilitypolarisability of the anion next to Liof the anion next to Li++

�� When a group of halide, FWhen a group of halide, F–– ; ; ClCl––; Br; Br––; I; I–– is put close to Liis put close to Li++, the , the

covalencycovalency of lithium halide of lithium halide increase when going down to increase when going down to covalencycovalency of lithium halide of lithium halide increase when going down to increase when going down to

Group 17 halide. Group 17 halide. LiFLiF is highly ionic, since the fluoride ion has is highly ionic, since the fluoride ion has

small ionic size and low charge, hence has low small ionic size and low charge, hence has low polarisabilitypolarisability. .

Ionic size increase with the increasing shell when going down Ionic size increase with the increasing shell when going down

to Group 17 halide, hence increase the to Group 17 halide, hence increase the polarisabilitypolarisability, which , which

allowed lithium ion to allowed lithium ion to polarisepolarise the anion’s electron density, the anion’s electron density,

hence increase the hence increase the covalencycovalency

Li+

F–

Br–

Cl–

AluminiumAluminium halidehalide (AlX(AlX33)) andand aluminiumaluminium oxideoxide (Al(Al22OO33))

�� AluminiumAluminium ionion (Al(Al33++)) hashas highhigh chargecharge density,density, duedue toto itsits highhigh

chargecharge unitunit andand itsits smallsmall ionicionic radiusradius.. So,So, dependingdepending onon thethe anion,anion,

aluminiumaluminium hashas aa highhigh tendencytendency toto formform covalentcovalent compoundcompound.. ForFor

example,example, whenwhen goinggoing downdown toto GroupGroup 1717 halide,halide, aluminiumaluminium fluoridefluoride

(AlF(AlF33)) formsforms ionicionic compoundcompound (since(since FF-- hashas aa lowlow polarisabilitypolarisability),),

whilewhile aluminiumaluminium trichloridetrichloride (AlCl(AlCl33),), aluminiumaluminium tribromidetribromide (AlBr(AlBr33))

andand aluminiumaluminium iodideiodide (AlI(AlI33)) formform covalentcovalent compoundcompound (since(since

chloride,chloride, bromidebromide andand iodideiodide havehave highhigh polarisabilitypolarisability)).. ThisThis

explainedexplained whywhy aluminiumaluminium fluoridefluoride hashas aa highhigh meltingmelting pointpointexplainedexplained whywhy aluminiumaluminium fluoridefluoride hashas aa highhigh meltingmelting pointpoint

((1040104000C),C), whilewhile aluminiumaluminium trichloridetrichloride andand tribromidetribromide areare 19219200CC andand

787800CC respectivelyrespectively..

�� AsAs forfor aluminiumaluminium oxideoxide (Al(Al22OO33),), itit isis anan ionicionic compoundcompound withwith highhigh

covalentcovalent characteristic,characteristic, asas aluminiumaluminium ionion hashas highhigh covalentcovalent

characteristiccharacteristic duedue toto itsits highhigh chargecharge densitydensity.. ThisThis explainedexplained thethe

highhigh meltingmelting pointpoint ofof AlAl22OO33 ((2050205000C)C) yetyet itit isis insolubleinsoluble inin waterwater.. ItIt

alsoalso explainedexplained thethe amphotericamphoteric propertiesproperties ofof aluminiumaluminium oxideoxide wherewhere

aluminiumaluminium oxideoxide cancan actact asas anan acidacid (covalent(covalent characteristic),characteristic), asas

wellwell asas aa basebase (ionic(ionic characteristic)characteristic)..

Metallic BondingMetallic Bonding

�� The properties of metals cannot be explained in terms of the The properties of metals cannot be explained in terms of the

ionic / covalent bond. In ionic / covalent compound, electron ionic / covalent bond. In ionic / covalent compound, electron

are not free to move under the influence of applied potential are not free to move under the influence of applied potential

(charge) difference. Therefore, ionic solid and covalent (charge) difference. Therefore, ionic solid and covalent

compound are compound are insulatorinsulator..

�� In metal, electron are In metal, electron are delocaliseddelocalised and metal atoms are and metal atoms are

effectively effectively ionisedionised. .

Metallic bond ~ electrostatic attraction between the positively Metallic bond ~ electrostatic attraction between the positively �� Metallic bond ~ electrostatic attraction between the positively Metallic bond ~ electrostatic attraction between the positively

charged metal ion and the electron charged metal ion and the electron delocaliseddelocalised..

�� Because of this, electron now can freely move from cathode Because of this, electron now can freely move from cathode

to anode when a metal is subjected to an electrical potential. to anode when a metal is subjected to an electrical potential.

The mobile electron can also conduct heat by carrying the The mobile electron can also conduct heat by carrying the

kinetic energy from a hot part of the metal to a cold part. This kinetic energy from a hot part of the metal to a cold part. This

electron electron delocaliseddelocalised can also use to explain the electrical can also use to explain the electrical

and thermal conductivities of metaland thermal conductivities of metal

The Band Theory : Overlapping of OrbitalThe Band Theory : Overlapping of Orbital

�� The number of molecular orbitals produced is equal to the The number of molecular orbitals produced is equal to the

number of atomic orbitals that overlap. number of atomic orbitals that overlap.

�� In a metal, the number of atomic orbitals that overlap is very In a metal, the number of atomic orbitals that overlap is very

large. Thus the number of molecular orbital produced is also large. Thus the number of molecular orbital produced is also

very large.very large.

�� The energy separations between these metal orbitals are The energy separations between these metal orbitals are

extremely small. So, we may regard the orbital as merging extremely small. So, we may regard the orbital as merging

together to form a continuous band of allowed energy state. together to form a continuous band of allowed energy state. together to form a continuous band of allowed energy state. together to form a continuous band of allowed energy state.

This collection of very closed molecular orbital energy levels This collection of very closed molecular orbital energy levels

is called an energy band. This theory for metal is called band is called an energy band. This theory for metal is called band

theorytheory

Electrical ConductorsElectrical Conductors

�� Molecular orbital model == 2 group of energy level.Molecular orbital model == 2 group of energy level.

�� Lower energy level Lower energy level –– valence band valence band → form from overlap of outer → form from overlap of outer

most orbital containing valence electron of each atom.most orbital containing valence electron of each atom.

�� Higher energy level Higher energy level –– conduction band conduction band → energy level filled with → energy level filled with

mobile electronmobile electron

�� But there are some case where valence band can also serve But there are some case where valence band can also serve

as conduction band (caused by the movement of delocalised as conduction band (caused by the movement of delocalised

molecular orbital)molecular orbital)molecular orbital)molecular orbital)

�� Electrical conductivities decrease when temperature Electrical conductivities decrease when temperature

increase increase –– vibration of the lattice of ion impedes the free vibration of the lattice of ion impedes the free

movement of electron in conduction band.movement of electron in conduction band.

conduction bandconduction band

valence bandvalence band

InsulatorInsulator

�� Difference between conductors, semiDifference between conductors, semi--conductors, and conductors, and

insulator depend on the energy gap between the 2 bands. insulator depend on the energy gap between the 2 bands.

�� Conductor Conductor –– 2 bands overlaps so conduction band always 2 bands overlaps so conduction band always

partly filled. partly filled.

�� Insulator Insulator –– gap between the band is large and no electron gap between the band is large and no electron

exist in the conduction band. E.g. insulator exist in the conduction band. E.g. insulator –– diamonddiamond

�� When 2s and 2p orbital of C is combine to form 2 energy When 2s and 2p orbital of C is combine to form 2 energy

bands, valence band is filled with electron.bands, valence band is filled with electron.

�� In insulator, the energy gap between the band is large. Under In insulator, the energy gap between the band is large. Under

normal condition, few electrons in valence band can jump normal condition, few electrons in valence band can jump

across to conduction band. If electron cannot reach across to conduction band. If electron cannot reach

conduction band across the gaps, the electrical conduction conduction band across the gaps, the electrical conduction

cannot take place.cannot take place.

Semiconductor Semiconductor

�� There’s still energy gaps between 2 bands in semiconductor, There’s still energy gaps between 2 bands in semiconductor,

but it is smaller than insulator. but it is smaller than insulator.

�� In semiconductor, some electrons have sufficient energy to In semiconductor, some electrons have sufficient energy to

jump across the energy gaps and electron can move freely jump across the energy gaps and electron can move freely

in conduction band thus enable electrical conduction.in conduction band thus enable electrical conduction.

�� Still, the electrical activity is not as good as metal (conductor) Still, the electrical activity is not as good as metal (conductor)

Increasing temperature can help to improve the conductivity Increasing temperature can help to improve the conductivity

because electron gain thermal energy and are able to reach because electron gain thermal energy and are able to reach because electron gain thermal energy and are able to reach because electron gain thermal energy and are able to reach

conduction band.conduction band.

�� It can also improve its effectiveness by adding small amount It can also improve its effectiveness by adding small amount

of substance. This adding is what we called doping. It can of substance. This adding is what we called doping. It can

help to increase electrons to fill in valence band. help to increase electrons to fill in valence band.

�� Example of doping is Si dope P (nExample of doping is Si dope P (n--type). Si dope Ge (ptype). Si dope Ge (p--type) type)

Depend on the needs, this process can help to create the Depend on the needs, this process can help to create the

various type of semiconductor in electronic characteristic.various type of semiconductor in electronic characteristic.

7.1 7.1 Van Van derder Waals forcesWaals forces

�� Van Van DerDer Waals forces are the intermolecular forces formed Waals forces are the intermolecular forces formed

between covalently bond molecules which exist as simple between covalently bond molecules which exist as simple

molecules.molecules.

�� There are 2 types of Van There are 2 types of Van DerDer Waals forces namelyWaals forces namely

♥♥ Permanent Dipole Permanent Dipole –– Permanent dipole forcesPermanent dipole forces

♥♥ Temporary dipole Temporary dipole –– induced dipole forcesinduced dipole forces

7.1.1 7.1.1 DipoleDipole--dipole attraction forcesdipole attraction forces

1. Polar molecule possessed dipole moment. Each of the polar 1. Polar molecule possessed dipole moment. Each of the polar

molecules have an overall magnitude. For example in hydrogen molecules have an overall magnitude. For example in hydrogen

chloridechloride

H H –––––––– ClCl

δδ+ + δδ––

2. The dipole inside polar molecules is permanent and the forces 2. The dipole inside polar molecules is permanent and the forces

between the molecule form as the positive end of dipole will between the molecule form as the positive end of dipole will

attract to the attract to the negative end of another molecule’s dipole.negative end of another molecule’s dipole.attract to the attract to the negative end of another molecule’s dipole.negative end of another molecule’s dipole.

3. This kind of forced are called permanent dipole3. This kind of forced are called permanent dipole--dipole forces.dipole forces.

4. The strength of the attraction depends on two factors : dipole 4. The strength of the attraction depends on two factors : dipole

moment and relative molecular massmoment and relative molecular mass

5. Higher the dipole moment 5. Higher the dipole moment –– the more polar the molecule the more polar the molecule ––

stronger the Van stronger the Van DerDer Waals forcesWaals forces

6. Comparisons were made between 4 molecules that have 6. Comparisons were made between 4 molecules that have

nearly equaled of molecular mass, but with different dipole nearly equaled of molecular mass, but with different dipole

momentmoment

Compounds RMM DM Boiling point (°C)Propane , CH3CH2CH3 44 0.1 - 18.0

Methyl methoxide, CH3–O–CH3 44 1.3 4.0

Chloromethane 50.5 1.9 6.0

7. Methyl cyanide exhibit the highest boiling point among the 3 7. Methyl cyanide exhibit the highest boiling point among the 3

molecules as it has the highest dipole moment among these molecules as it has the highest dipole moment among these

molecules, which makes the attraction between the dipolemolecules, which makes the attraction between the dipole--

dipole attraction become stronger, anddipole attraction become stronger, and required a higher required a higher

temperature to break the attraction forces among CHtemperature to break the attraction forces among CH33CNCN----------

CHCH33CNCN..

Chloromethane 50.5 1.9 6.0

Methyl cyanide, CH3CN 41 3.9 56.0

8. Another factor which influence the strength of permanent 8. Another factor which influence the strength of permanent

dipoledipole--dipole forces, are the factor of relative molecular dipole forces, are the factor of relative molecular

mass. mass.

9. Higher the mass, stronger the forces of attraction ( Van 9. Higher the mass, stronger the forces of attraction ( Van DerDer

Waals forces ), higher the boiling point or melting point of the Waals forces ), higher the boiling point or melting point of the

substancesubstance

RMMMelting

point (°C)Boiling

point (°C)RMMpoint (°C) point (°C)

Hydrogen chloride, H – Cl 36.5 - 114 - 85

Hydrogen bromide, H – Br 81.0 - 87 - 66

Hydrogen iodide, H – I 128 - 51 - 35

7.1.2 Temporary dipole 7.1.2 Temporary dipole –– induce dipole forcesinduce dipole forces

�� NonNon--polar molecules have a dipole moment = 0. polar molecules have a dipole moment = 0. Basically, they won’t have any attraction between the Basically, they won’t have any attraction between the molecules as there are no significant poles with molecules as there are no significant poles with charge in the molecule, so how they interact ??!!!charge in the molecule, so how they interact ??!!!

�� For nonFor non--polar molecules, they may have a chance to polar molecules, they may have a chance to form asymmetrical structure, as the distribution of form asymmetrical structure, as the distribution of electron within the molecule are not even, giving the electron within the molecule are not even, giving the atom a temporary dipole moment.atom a temporary dipole moment.

�� During the During the formation of temporary dipole momentformation of temporary dipole moment, , �� During the During the formation of temporary dipole momentformation of temporary dipole moment, , induction process takes place where the distribution of induction process takes place where the distribution of electron are uneven and give the atom which are electron are uneven and give the atom which are temporary rich of electron to form dipole. These temporary rich of electron to form dipole. These dipoles also known as induce dipole.dipoles also known as induce dipole.

�� When induced dipole is formed , a temporary When induced dipole is formed , a temporary interaction between the molecules formed and interaction between the molecules formed and produces weak forces among them.produces weak forces among them.

�� This theory is introduced by This theory is introduced by FriteFrite London in 1930. It is known London in 1930. It is known

as London dispersion forces.as London dispersion forces.

�� In (a) the nonIn (a) the non--polar molecule which does not have a dipole polar molecule which does not have a dipole �� In (a) the nonIn (a) the non--polar molecule which does not have a dipole polar molecule which does not have a dipole

within the molecule begin to fluctuate and thus forming a within the molecule begin to fluctuate and thus forming a

“temporary” dipole as in (b). Thus the forces of attraction will “temporary” dipole as in (b). Thus the forces of attraction will

formed between the temporary dipole and this forces is formed between the temporary dipole and this forces is

named as named as London ForcesLondon Forces

7.2 Effect of the intermolecular forces ( Van 7.2 Effect of the intermolecular forces ( Van derder waalswaals ) on the ) on the

physical properties of the moleculesphysical properties of the molecules

�� ��H H vapourisationvapourisation�� give a quantitative measurement of strength of give a quantitative measurement of strength of

attractive forces present in liquid. So, attractive forces present in liquid. So, ����H H vapourisationvapourisation , , �� thethe

boiling point , boiling point , �� the intermolecular forces among its molecules. the intermolecular forces among its molecules.

�� When a molecule increase in size, the number of electron also When a molecule increase in size, the number of electron also

increase, so the increase, so the attraction between the electron valence and attraction between the electron valence and

nucleus become lessnucleus become less. This distortion of electron cloud can easily . This distortion of electron cloud can easily

occur and increase the occur and increase the polarisabilitypolarisability of the negative ion. of the negative ion. occur and increase the occur and increase the polarisabilitypolarisability of the negative ion. of the negative ion.

�� This can be relating with the dispersion forces among molecules This can be relating with the dispersion forces among molecules

therefore therefore ��H H vapourisationvapourisation �� , e.g. : Value of boiling point of , e.g. : Value of boiling point of

halogen gas increase. halogen gas increase. ( from F( from F2 2 �� II22 ))

�� In hydrocarbon, boiling point increase with relative molecular In hydrocarbon, boiling point increase with relative molecular

mass (RMM). Molecule with higher RMM will have a higher mass (RMM). Molecule with higher RMM will have a higher

boiling point.boiling point.

�� The effect of branched chain in hydrocarbon will also affect the The effect of branched chain in hydrocarbon will also affect the

boiling point of hydrocarbon involvedboiling point of hydrocarbon involved

Structure RMM Boiling point

(°C)

2,2–dimethyl

propane72 4

2-methylbutane 72 18

�� This is due to a larger surface area in a straight chain of This is due to a larger surface area in a straight chain of

hydrocarbon, and allows greater forces between the hydrocarbon, and allows greater forces between the

molecules molecules –– giving larger Van giving larger Van derder Waals forces Waals forces –– compare to compare to

branch chain hydrocarbonbranch chain hydrocarbon

2-methylbutane 72 18

n–pentane CH3 – CH2 – CH2 – CH2 – CH3 72 36

7.3 7.3 Hydrogen BondingHydrogen Bonding

�� Hydrogen bond is a Hydrogen bond is a special dipolespecial dipole––dipole interaction between dipole interaction between

H atom with otherH atom with other atom with high atom with high electronegativityelectronegativity. ( N, O, F ). ( N, O, F )

�� It is extra stable than normal Van It is extra stable than normal Van derder waalswaals forces and forces and

required a high energy to break the bond. This explained why required a high energy to break the bond. This explained why

the boiling point of NHthe boiling point of NH33, H, H22O and HF are higher than other O and HF are higher than other

hydrogen compound from each of their particular group.hydrogen compound from each of their particular group.

��Decreasing molar massDecreasing molar mass

��Decreasing boiling pointDecreasing boiling point

�� Hydrogen bond can also be used to explain the different of Hydrogen bond can also be used to explain the different of

boiling point of some organic compound. In the diagram above, boiling point of some organic compound. In the diagram above,

the trend of the compound in the same group deviates for N, O the trend of the compound in the same group deviates for N, O

and F, as it form hydrogen bond among themselves. and F, as it form hydrogen bond among themselves.

�� Hydrogen bond can be compared among NHHydrogen bond can be compared among NH33 , H, H22O and HF. O and HF.

HF has a higher boiling point than NHHF has a higher boiling point than NH33 due to higher due to higher

electronegativityelectronegativity of fluorine compare to nitrogen. So the dipole of fluorine compare to nitrogen. So the dipole

moment of Hmoment of H––F is greater than NF is greater than N––H, which results greater H, which results greater

hydrogen bond. Though, O has a lower hydrogen bond. Though, O has a lower electronegativityelectronegativity than F, than F,

but Hbut H22O has a greater boiling point compare to HF because in O has a greater boiling point compare to HF because in

between Hbetween H22O O -------- HH22O molecules, they can form 2 hydrogen O molecules, they can form 2 hydrogen

bond between the molecule but between HF bond between the molecule but between HF ------ HF can only HF can only

form one hydrogen bond. So, the more the hydrogen formed, form one hydrogen bond. So, the more the hydrogen formed,

greater the forces, higher the boiling point.greater the forces, higher the boiling point.

�� The factors of hydrogen bonding can also use to explain the The factors of hydrogen bonding can also use to explain the

solubility of some organic compound in water, like example, solubility of some organic compound in water, like example,

ethane cannot dissolve in water but ethanol can dissolve in ethane cannot dissolve in water but ethanol can dissolve in

water, due to the hydrogen bonding.water, due to the hydrogen bonding.

�� Some of the molecules gain more stability by forming Some of the molecules gain more stability by forming dimerdimer

with its moleculeswith its molecules. E.g. : When . E.g. : When ethanoicethanoic acid is brought to acid is brought to

mass spectrometer for detection and it gives a peak at m/e at mass spectrometer for detection and it gives a peak at m/e at

120. This indicates the shows that120. This indicates the shows that ethanoicethanoic acid (CHacid (CH33COOH) COOH)

has a RMM of 120, as CHhas a RMM of 120, as CH33COOH , RMM = 60.COOH , RMM = 60.

�� This indicate This indicate ethanoicethanoic acid exist as acid exist as dimerdimer where interaction of where interaction of

hydrogen bonding between end of each functioning group hydrogen bonding between end of each functioning group ––

COOH occur.COOH occur.

�� There is another application of hydrogen bond, which is the There is another application of hydrogen bond, which is the

intermolecular forces and intermolecular forces and intramolecularintramolecular forces. In 2forces. In 2--

nitrophenol and 4nitrophenol and 4--nitrophenol, the boiling point of the 2 nitrophenol, the boiling point of the 2

compounds can be explain below :compounds can be explain below :

�� Since 2Since 2--nitrophenol form strong hydrogen bond as nitrophenol form strong hydrogen bond as

intramolecularintramolecular forces, the interaction between 2forces, the interaction between 2--nitrophenol nitrophenol

molecules are weaker among each other, compare to 4molecules are weaker among each other, compare to 4--

nitrophenol, which used hydrogen bond as their nitrophenol, which used hydrogen bond as their

intermolecular forces. With stronger hydrogen bond which act intermolecular forces. With stronger hydrogen bond which act

as the intermolecular forces, the boiling point of 4as the intermolecular forces, the boiling point of 4--nitrophenol nitrophenol

is expected to be higher than 2is expected to be higher than 2--nitrophenolnitrophenol