4.1 LEWIS STRUCTURE

CHAPTER 4:
CHEMICAL BONDING

4.1 DRAW LEWIS SK015

STRUCTURE 4.0 CHEMICAL BONDING

a) Write Lewis dot symbol for an atom (C1,C2) OVERVIEW

b) State octet rule and describe how

atoms obtain the octet configuration (C2) 4.3 ORBITAL OVERLAP AND

c) Describe formation of following HYBRIDISATION

bonds using Lewis dot symbol a) Draw and describe the formation of 

a) Ionic/electrovalent bond (C2,C3) (sigma) and  (pi) bond from
b) Covalent bond overlapping of orbitals (C2)

c) Dative/coordinate bond 4.4 INTERMOLECULAR FORCES

d) Draw Lewis structure of covalent b) Describe the formation of hybrid

species with single, double and triple a) Describe intermolecular forces orbitals of the centre atom

bonds (C2,C3) i. van der Waals forces i) sp

e) Compare the bond length between - dipole-dipole forces (C2) ii) sp2 (C3,C4)
- London forces iii) sp3
single, double and triple bonds (C2)
ii. hydrogen bonding iv) sp3d
f) Determine the formal charge and
b) Exp factors that influence v) sp3d2
most plausible Lewis structure (C3)
- van der Waals forces c) Illustrate the hybridization of the
g) Exp the exception of the octet rule (C3,C4)
- hydrogen bond central atom and the overlapping of
-Incomplete octet
-Expanded octet (C2) c) Relate the effects of H-bonding on : orbitals in molecules (C3)

-Odd number electrons i. boiling point

h) Illustrate the concept of resonance ii. solubility (C4)
using appropriate examples (C3)
iii. density of water compared to ice

4.2 MOLECULAR SHAPE AND POLARITY 4.5 METALLIC BOND

a) Explain VSEPR theory (C2) a) Exp the formation of metallic bond by using electron sea

b) Draw basic molecular shape model (C2)

i) linear ii) trigonal planar (C2) b) Relate metallic bond to the properties of metal

iii) tetrahedral iv) trigonal bipyramidal i) malleability ii) ductility (C3)

v) octahedral iii) electrical conductivity iv) thermal conductivity

c) Predict and exp the shapes of molecules and bond angles in a c) Exp factors that effect the strength of metallic bond (C2)

given species (C3,C4) d) Relate boiling point/melting point to the molecular

d) Exp bond polarity and dipole moment (C2,C3) structure, types of bonding and intermolecular forces for

e) Deduce polarity molecule based on the shape and the elements of period 3. group 1 & group 17 (C3)

resultant dipole moment (C3,C4)

4.1 Lewis structure

At the end of this lesson, students should be able to :
a) write the Lewis dot symbol for an atom.

b) state the octet rule and describe how atoms obtain the
octet configuration

c) describe the formation of the following bonds
using Lewis dot symbol.

i. Ionic or electrovalent bond
ii. Covalent bond
iii. Dative or coordinate bond

4.1 Lewis structure

At the end of this lesson, students should be able to :
d) draw Lewis structure of covalent species with

single, double and triple bonds.

e) compare the bond length between single,
double and triple bonds.

LEWIS DOT SYMBOL

Consist of
- CHEMICAL/ELEMENT SYMBOL to represent the

NUCLEUS and INNER ELECTRON (inner shell) of an atom
- together with DOTS placed around the symbol to

represent the VALENCE ELECTRON (outer-shell)

Na 

Na : 1s2 2s2 2p6 3s1

Valence electron: involved in chemical bonding

RELATIONSHIP BETWEEN
GROUP AND VALENCE ELECTRON

Group valence e- No. of valence e-
configuration

1 ns1 1

2 ns2 2

13 ns2 np1 3

14 ns2 np2 4

15 ns2 np3 5

16 ns2 np4 6

17 ns2 np5 7

18 ns2 np6 8

Valence electrons are the outer shell electrons of
an atom which participate in chemical bonding.

HOW TO WRITE LEWIS DOT SYMBOL

EXAMPLE: valence electrons N

N (Z = 7 )

Electron configuration: 1s2 2s2 2p3

1. Identify the number of valence electrons of element

2. Place one dot at a time on the four side
(top, right, bottom, left) of the element symbol

 Consider the electron repulsion

3. Pair up the dots until all are used

EXAMPLE – 01

Give the group number and valence electron
configuration of an element with the following
Lewis dot symbols:

a) ●●X●● ●● b) ●

X●
●

c) ●● d) ●X● ●

●X● ●
●

Ans: EXAMPLE – 01

a) ●●X●●● b) X●●

● ●

 6 dots  3 dots
 6 valence electrons  3 valence electrons
 Group 16  Group 13

 ns2 np4  ns2 np1

c) ●● d) ●

● X● ●X●
●
●

 5 dots  4 dots

 5 valence electrons  4 valence electrons

 Group 15  Group 14

 ns2 np3  ns2 np2

Lewis dot symbol for N:

 N 

Also can be written as:

   or  or   
N N N



Lewis dot symbol do not show the electronic configuration
of the valence electrons!

Example: valence electrons
B (Z = 5 )

1s 2s 2p
Electron configuration: 1s2 2s2 2p1

  correct

B  B 

B has three unpaired dots because it form three bonds

LEWIS DOT SYMBOL OF ELEMENTS

Element in the same group
 similar valence electron configuration
 similar Lewis dot symbol

Number of unpaired dots allowed to predict
- number of electrons a metal atom loses
- number of electrons a nonmetal gains
- number of covalent bonds a nonmetal atom usually forms

EXAMPLE :

 Na

Na loses one electron to form Na+ (+1 charge)


 N 
N gains three electrons to form N3– (-3 charge)

N can form three covalent bonds

 

Cl 


Cl gains one electron to form Cl– (–1 charge).

Cl can form one covalent bond

Lewis Dot Diagrams of Selected Elements

He

OCTET RULE

ATOMS (other than H) tend to form a BOND
 by losing and gaining or sharing electrons
 until it is surrounded by EIGHT VALENCE

ELECTRONS

The rule works mainly for some elements
in Period 2

OCTET RULE

Atoms may lose or gain enough electrons
so as to form stable ion with octet (or duplet)
configuration (stable configuration of ion).

 ns2 np6

Maximum stability results when an atom is
isoelectronic with a noble gas.

EXAMPLE – 03

In which of the following bonding patterns does
X obey the octet rule?

a) X c)
X

b) X ●● d) ●●●●X●●●●2–

Ans: EXAMPLE – 03

a) X  X surrounded by 8 valence electrons
 Obey octet rule

b) X ●●  X surrounded by 8 valence electrons
 Obey octet rule

c)  X surrounded by 6 valence electrons
X  Do not obey octet rule

d) ●●●●X●●●●2–  X surrounded by 8 valence electrons
 Obey octet rule

TYPES OF CHEMICAL BONDING

1 IONIC/ELECTROVALENT BOND

2 COVALENT BOND NaCl

3 DATIVE BOND / Coordinate Covalent Bond

+

IONIC BOND

Sometimes called electrovalent bond

formed between metal & nonmetal elements

 metal atoms donate electron to form
positive ions while non-metals accept
electron to form negative ions.

ionic bond is electrostatic force between

positive and negative ions that hold them
together in solid crystal.

Na+ ●●●●C●●l●●–

By transferring electrons from metal element and
that electrons is gaining by non metal element

EXAMPLE:

Li Li+ + e-
1s22s1
1s2
e- + F F–
1s22s22p5 1s22s22p6

Li+ + F – [Li]+ [F] –

Total number of = Total number of
Electrons lost electrons gained
by metal atoms by the nonmetal atoms

HOW TO SHOW ELECTRON TRANSFER

By using Lewis dot symbol

EXAMPLE:

Na● + ●● ●● [Na]+ ●● ●● ●● –

●Cl Cl

●● ●●

Formation can be described by Lewis dot symbol
(valence e- represented as dot or cross).

Na• 2-

+ xx 2[Na] + x• xx •x

Na• xO x O
xx
xx

(formation of electrovalent bond )

Formation
of NaF

[Na] + xx -

x• F x

xx

Formation
of MgO

2+ 2-

EXERCISE – 01

Use Lewis dot symbols to depict
monoatomic ions formed from each of the
following reactants and predict the formula of
the compound the ions produce:
a)
b) a) Al and F

c) b) K and O

Ans: EXERCISE – 01

a) Al: 1s2 2s2 2p6 3s2 3p1
F: 1s2 2s2 2p5

Lewis dot symbol:

●● 33+ ●● –

● F ●● Al ●● ●F●●●

● Al ● + ●●
●
●
●● F ●●
Al3+: 1s2 2s2 2p6 3s2 3p1
●● F-: 1s2 2s2 2p5

● ●F●●●

●●

EXERCISE – 01

b) K : 1s2 2s2 2p6 3s2 3p6 4s1
O : 1s2 2s2 2p4

Lewis dot symbol:

K● ●● 2–

●● 2 [K]+ ●● O ●●

+ ●O● ●●

●● K+ : 1s2 2s2 2p6 3s2 3p6
O2- : 1s2 2s2 2p6
K●

COVALENT BOND

Bond in which two electrons are shared by
two atoms

Non-metals and non-metals
Non-metals and metals (difference in

electronegativity between two atoms is small)

 BeCl2 , AlCl3

EXAMPLE:

H—H ●● ●●

●●●F● ●●●F●●●

Formation
of H2

covalent bond

Formation
of I2

covalent bond

Formation
of HCl

covalent bond

In general number of covalent bonds for the elements :

Fam ily  # Covalent Bonds*

H alo g e n s X 1 bond often
F, Br, C l, I O 2 bonds often
N 3 bonds often
C alcogens C 4 bonds always
O, S

N itro g e n
N, P

C arbon
C, Si

The above chart is a guide on the number of bonds formed by these atoms.

Pauling scale (devised by Linus Pauling in 1932) - electronegativity
difference between two atoms is greater than or equal to 1.7, the bond
between them is usually considered ionic; for values between 1.7 and 0.4, the
bond is considered polar covalent.

A metal and a nonmetal have a relatively
large EN (difference in electronegativity)
and typically forms an ionic compound

EXAMPLE:

NaCl EN = 2.1  strong ionic character

But compounds with relatively small EN
such as AlCl3, BeCl2 and BF3 show covalent
character

As EN becomes smaller, the bond becomes
more covalent

EXERCISE - 02

1. Show formation of covalent bond in oxygen
molecule.

Ans; EXERCISE - 02

1. Show formation covalent bond in oxygen gas.

Comparison of Two Types of Bonding

Covalent Bonds Ionic Bonds
-A sharing of two or -An attraction that occurs
more electrons between ions of opposite
between atoms. charge.

-When two atoms -Metals and nonmetals are
combine they do so by held together with ionic
the formation of bonds.
covalent bonds. -Polyatomic ions also form
ionic bonds.
(e.g. ammonium chloride,
NH4Cl)

EXAMPLE - 04

State the type of bonding; ionic or covalent bond?

a) CsF(s)
b) N2(g)
c) ICl3(g)
d) N2O(g)
e) LiCl(s)

Ans: EXAMPLE – 04

a) CsF(s) c) ICl3(g)
 Metal and nonmetal  Nonmetal and nonmetal
 Ionic bond  Covalent bond

b) N2(g) d) N2O(g)
 Nonmetal and nonmetal  Nonmetal and nonmetal
 Covalent bond  Covalent bond

e) LiCl(s)
 Metal and nonmetal
 Ionic bond

DATIVE BOND

Also called Coordinate covalent bond

Definition:

DATIVE BOND is a type of covalent bond in
which the shared pair of electrons are
contributed by only one of the bonded atoms.

Dative bond is shown by an arrow (→) pointing
from the donor atom to the acceptor atom.

A donor must contain at least one lone pair
of electrons.

+

EXAMPLE : formation ammonium ion

H+ + H ammonium ion (NH4+)
 N H +

H H
H NH

H

Arrow pointing from
donor to acceptor

(Dative bond)

Example: formation hydroxonium ion

.. .. +
H
O: + H+ O
HH
H
H

Arrow pointing from
donor to acceptor

(Dative bond)

Example: Al2Cl6

H H+
H+  N H H NH

H H

No difference between normal covalent bond
and covalent dative bond

EXAMPLE: bond length and strength of the
four N–H bonds are same

EXERCISE - 02

1. Boron trifluoride (BF3) accepts an electron pair
from ammonia (NH3) to form BF3NH3.
Show which of the bond is the coordinate
covalent bond?

2. Aluminum trichloride (AlCl3) reacts with
diethyl ether to form a new molecule.
Show which of the bond is the coordinate
covalent bond?

Ans: EXERCISE - 02

1. F H F H
••N H NH
B+ B
FF H F H

F

Dative bond

2. Et—●O●●● Cl Cl
Et + Al
●●
Cl Cl
Et—O—Al—Cl

Et Cl

Dative bond

LEWIS STRUCTURE

Is a combination of Lewis symbol that represents either the

transfer or sharing of electrons in a chemical bond.
A structural formula consists of electron–dot symbols

that show atom and its neighbors, the bonding pairs
and the lone pairs that fill each atom’s outer shell

  
 F N F 

Types of pair electrons F

 Bonding pair electron  lone pair electron

Types of bonding  Double bond  Triple bond
 Single bond

TYPES OF PAIR ELECTRON

BONDING PAIR ELECTRON

The two electrons that form covalent bond
 Shared electron pair

LONE PAIR ELECTRON

Pairs of valence electrons that not involved
in bonding  Unshared electron pair

EXAMPLE: lone pair

●● ●● ●● ●●

●●●F●—●F●●● or ● F ● F ●
● ● ●
●● ●●

bonding pair

TYPES OF BONDING

SINGLE BOND

One bonding pair of electrons

EXAMPLE:

single bond or H●H
H—H ●

●●●●F●●—●●F●●●● or ●●●●F●● ●●●●F●●●●
H—●●O●●—H or H ●●●●O●●●● H