Chemical Bonding - Chemical Bonding & Molecular Structure - Class 11

 Page 1


48 
 
CHAPTER-4 
 CHEMICAL BONDING AND MOLECULAR STRUCTURE 
OCTET RULE- During a chemical reaction the atoms tend to adjust their 
electronic arrangement in such a way that they achieve 8 e
-
 in their outermost 
electron. This is called octet rule. 
CHEMICAL BOND- the chemical force which keeps the atoms in any molecule 
together is called a chemical bond. 
IONIC BOND- The columbic force of attraction which holds the appositively 
charged ions together is called an ionic bond. An ionic bond is formed by the 
complete transfer of one or more electrons from the atom of a metal to an atom of 
non- metal. 
LATTICE ENTHALPY- The molar enthalpy change accompanying the complete 
separation of the constituent particles that compose of the solids (such as ions for 
ionic solid, molecules for molecular solids) under standard conditions is called 
lattice enthalpy (?
l
H
o
). The lattice enthalpy is a positive quantity. 
ELECTRO VALENCY: The number of electrons lost or gain by an atom of an 
element is called as electrovalency. 
The element which give up electrons to form positive ions are said to have positive 
valency, while the elements which accept electrons to form negative ions are said to 
have negative valency. 
FORMATION OF AN IONIC BOND: It is favoured by, (i) the low ionisation 
enthalpy of a metallic element which forms the cations, (ii) High electron gain 
enthalpy of non- metallic element which forms the anions, (iii) Large lattice 
enthalpy i.e; the smaller size and the higher charge of the atoms. 
COVALENCY:The number of electrons which an atom contributes towards 
mutual sharing during the formation of a chemical bond called its covalency in that 
compound.       
SINGLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
one pair of electrons is called a single covalent bond, or simply a single bond. A 
single covalent bond is represented by a small line (-) between the two atoms. 
Page 2


48 
 
CHAPTER-4 
 CHEMICAL BONDING AND MOLECULAR STRUCTURE 
OCTET RULE- During a chemical reaction the atoms tend to adjust their 
electronic arrangement in such a way that they achieve 8 e
-
 in their outermost 
electron. This is called octet rule. 
CHEMICAL BOND- the chemical force which keeps the atoms in any molecule 
together is called a chemical bond. 
IONIC BOND- The columbic force of attraction which holds the appositively 
charged ions together is called an ionic bond. An ionic bond is formed by the 
complete transfer of one or more electrons from the atom of a metal to an atom of 
non- metal. 
LATTICE ENTHALPY- The molar enthalpy change accompanying the complete 
separation of the constituent particles that compose of the solids (such as ions for 
ionic solid, molecules for molecular solids) under standard conditions is called 
lattice enthalpy (?
l
H
o
). The lattice enthalpy is a positive quantity. 
ELECTRO VALENCY: The number of electrons lost or gain by an atom of an 
element is called as electrovalency. 
The element which give up electrons to form positive ions are said to have positive 
valency, while the elements which accept electrons to form negative ions are said to 
have negative valency. 
FORMATION OF AN IONIC BOND: It is favoured by, (i) the low ionisation 
enthalpy of a metallic element which forms the cations, (ii) High electron gain 
enthalpy of non- metallic element which forms the anions, (iii) Large lattice 
enthalpy i.e; the smaller size and the higher charge of the atoms. 
COVALENCY:The number of electrons which an atom contributes towards 
mutual sharing during the formation of a chemical bond called its covalency in that 
compound.       
SINGLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
one pair of electrons is called a single covalent bond, or simply a single bond. A 
single covalent bond is represented by a small line (-) between the two atoms. 
49 
 
DOUBLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
two pair of electrons is called a double covalent bond, or simply a double bond. A 
double covalent bond is represented by two small horizontal lines (=) between the 
two atoms. E.g. O=O, O=C=O etc. 
TRIPLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
three pair of electrons is called a triple covalent bond, or simply a triple bond. A 
triple covalent bond is represented by three small horizontal lines (=) between the 
two atoms. E.g. N=N, H-C=C-H etc. 
FORMATION OF A COVALENT BOND: Formation of a covalent bond is 
favoured by 
(i) High ionisation enthalpy of the combining elements. 
(ii) Nearly equal electron gain enthalpy and equal electro-negativities of 
combining elements. 
(iii) High nuclear charge and small atomic size of the combining elements. 
POLAR COVALENT BOND: The bond between two unlike atoms which differ 
in their affinities for electrons is said to be polar covalent bond. E.g. H-Cl  
COORDINATE BOND: The bond formed when one sided sharing of electrons 
take place is called a coordinate bond. Such a bond is also known as dative bond. It 
is represented by an arrow (?) pointing towards the acceptor atom. E.g. H
3N
?BF
3 
Bond Length: Bond length is defined as the equilibrium distance between the 
nuclei of two bonded atoms in a molecule 
Bond Angle: It is defined as the angle between the orbitals containing bonding 
electron pairs around the central atom in a molecule/complex ion 
Bond Enthalpy: It is defined as the amount of energy required to break one mole 
of  bonds of a particular type between two atoms in a gaseous state. 
Bond Order: In the Lewis description of covalent bond, the Bond Order is given 
by the number of bonds between the two atoms in a molecule 
Resonance:whenever a single Lewis structure cannot describe a molecule 
accurately, a number of structures with similar energy, positions of nuclei, bonding 
and non-bonding pairs of electrons are taken as the canonical structures of the 
hybrid which describes the molecule accurately 
Dipole moment : The product of the magnitude of the charge and the distance 
between the centres of positive and negative charge.It is a vector quantity and is 
represented by an arrow with its tail at the positive centre and head pointing towards 
a negative centre. Dipole moment ( µ) = charge (Q) × distance of separation (r) 
 
Page 3


48 
 
CHAPTER-4 
 CHEMICAL BONDING AND MOLECULAR STRUCTURE 
OCTET RULE- During a chemical reaction the atoms tend to adjust their 
electronic arrangement in such a way that they achieve 8 e
-
 in their outermost 
electron. This is called octet rule. 
CHEMICAL BOND- the chemical force which keeps the atoms in any molecule 
together is called a chemical bond. 
IONIC BOND- The columbic force of attraction which holds the appositively 
charged ions together is called an ionic bond. An ionic bond is formed by the 
complete transfer of one or more electrons from the atom of a metal to an atom of 
non- metal. 
LATTICE ENTHALPY- The molar enthalpy change accompanying the complete 
separation of the constituent particles that compose of the solids (such as ions for 
ionic solid, molecules for molecular solids) under standard conditions is called 
lattice enthalpy (?
l
H
o
). The lattice enthalpy is a positive quantity. 
ELECTRO VALENCY: The number of electrons lost or gain by an atom of an 
element is called as electrovalency. 
The element which give up electrons to form positive ions are said to have positive 
valency, while the elements which accept electrons to form negative ions are said to 
have negative valency. 
FORMATION OF AN IONIC BOND: It is favoured by, (i) the low ionisation 
enthalpy of a metallic element which forms the cations, (ii) High electron gain 
enthalpy of non- metallic element which forms the anions, (iii) Large lattice 
enthalpy i.e; the smaller size and the higher charge of the atoms. 
COVALENCY:The number of electrons which an atom contributes towards 
mutual sharing during the formation of a chemical bond called its covalency in that 
compound.       
SINGLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
one pair of electrons is called a single covalent bond, or simply a single bond. A 
single covalent bond is represented by a small line (-) between the two atoms. 
49 
 
DOUBLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
two pair of electrons is called a double covalent bond, or simply a double bond. A 
double covalent bond is represented by two small horizontal lines (=) between the 
two atoms. E.g. O=O, O=C=O etc. 
TRIPLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
three pair of electrons is called a triple covalent bond, or simply a triple bond. A 
triple covalent bond is represented by three small horizontal lines (=) between the 
two atoms. E.g. N=N, H-C=C-H etc. 
FORMATION OF A COVALENT BOND: Formation of a covalent bond is 
favoured by 
(i) High ionisation enthalpy of the combining elements. 
(ii) Nearly equal electron gain enthalpy and equal electro-negativities of 
combining elements. 
(iii) High nuclear charge and small atomic size of the combining elements. 
POLAR COVALENT BOND: The bond between two unlike atoms which differ 
in their affinities for electrons is said to be polar covalent bond. E.g. H-Cl  
COORDINATE BOND: The bond formed when one sided sharing of electrons 
take place is called a coordinate bond. Such a bond is also known as dative bond. It 
is represented by an arrow (?) pointing towards the acceptor atom. E.g. H
3N
?BF
3 
Bond Length: Bond length is defined as the equilibrium distance between the 
nuclei of two bonded atoms in a molecule 
Bond Angle: It is defined as the angle between the orbitals containing bonding 
electron pairs around the central atom in a molecule/complex ion 
Bond Enthalpy: It is defined as the amount of energy required to break one mole 
of  bonds of a particular type between two atoms in a gaseous state. 
Bond Order: In the Lewis description of covalent bond, the Bond Order is given 
by the number of bonds between the two atoms in a molecule 
Resonance:whenever a single Lewis structure cannot describe a molecule 
accurately, a number of structures with similar energy, positions of nuclei, bonding 
and non-bonding pairs of electrons are taken as the canonical structures of the 
hybrid which describes the molecule accurately 
Dipole moment : The product of the magnitude of the charge and the distance 
between the centres of positive and negative charge.It is a vector quantity and is 
represented by an arrow with its tail at the positive centre and head pointing towards 
a negative centre. Dipole moment ( µ) = charge (Q) × distance of separation (r) 
 
50 
 
SIGMA BOND: A covalent bond formed due to the overlapping of orbitals of the 
two atoms along the line joining the two nuclei (orbital axis) is called sigma (s) 
bond. For example, the bond formed due to s-s and s-p, p-p overlapping along the 
orbital axis are sigma bonds. 
Pi- BOND: A covalent bond formed by the side wise overlapping of p- or d- 
orbitals of two atoms is called as pi (p) bond. For example, the bond formed due to 
the sideways overlapping of the two p- orbitals is a pi- bond. 
HYDROGEN BOND: The bond between the hydrogen atom of one molecule and 
a more electro- negative element of same or another molecule is called as hydrogen 
bond. 
HYBRIDIZATION: The process of mixing of the atomic orbitals to form new 
hybrid orbitals is called hybridization. All hybrid orbitals of a particular kind have 
equal energy, identical shapes and are symmetrically oriented in shape. 
The hybrid orbitals are designed according to the type and the atomic orbitals 
merging together, e.g.,  
 
Molecu
le Type 
Shape 
Electron 
arrangeme
nt
†
 
     
Geometry
‡
 
Examples 
AX
2
E
0
 Linear 
 
 
 BeCl
2
, HgCl
2
, CO
2
 
AX
2
E
1
 Bent 
 
 
 NO
2
-
, SO
2
, O
3
, CCl
2
 
AX
2
E
2
 Bent 
 
 
 H
2
O, OF
2
 
AX
2
E
3
 Linear 
 
 
 XeF
2
, I
3
-
, XeCl
2
 
Page 4


48 
 
CHAPTER-4 
 CHEMICAL BONDING AND MOLECULAR STRUCTURE 
OCTET RULE- During a chemical reaction the atoms tend to adjust their 
electronic arrangement in such a way that they achieve 8 e
-
 in their outermost 
electron. This is called octet rule. 
CHEMICAL BOND- the chemical force which keeps the atoms in any molecule 
together is called a chemical bond. 
IONIC BOND- The columbic force of attraction which holds the appositively 
charged ions together is called an ionic bond. An ionic bond is formed by the 
complete transfer of one or more electrons from the atom of a metal to an atom of 
non- metal. 
LATTICE ENTHALPY- The molar enthalpy change accompanying the complete 
separation of the constituent particles that compose of the solids (such as ions for 
ionic solid, molecules for molecular solids) under standard conditions is called 
lattice enthalpy (?
l
H
o
). The lattice enthalpy is a positive quantity. 
ELECTRO VALENCY: The number of electrons lost or gain by an atom of an 
element is called as electrovalency. 
The element which give up electrons to form positive ions are said to have positive 
valency, while the elements which accept electrons to form negative ions are said to 
have negative valency. 
FORMATION OF AN IONIC BOND: It is favoured by, (i) the low ionisation 
enthalpy of a metallic element which forms the cations, (ii) High electron gain 
enthalpy of non- metallic element which forms the anions, (iii) Large lattice 
enthalpy i.e; the smaller size and the higher charge of the atoms. 
COVALENCY:The number of electrons which an atom contributes towards 
mutual sharing during the formation of a chemical bond called its covalency in that 
compound.       
SINGLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
one pair of electrons is called a single covalent bond, or simply a single bond. A 
single covalent bond is represented by a small line (-) between the two atoms. 
49 
 
DOUBLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
two pair of electrons is called a double covalent bond, or simply a double bond. A 
double covalent bond is represented by two small horizontal lines (=) between the 
two atoms. E.g. O=O, O=C=O etc. 
TRIPLE COVALENT BOND: A covalent bond formed by the mutual sharing of 
three pair of electrons is called a triple covalent bond, or simply a triple bond. A 
triple covalent bond is represented by three small horizontal lines (=) between the 
two atoms. E.g. N=N, H-C=C-H etc. 
FORMATION OF A COVALENT BOND: Formation of a covalent bond is 
favoured by 
(i) High ionisation enthalpy of the combining elements. 
(ii) Nearly equal electron gain enthalpy and equal electro-negativities of 
combining elements. 
(iii) High nuclear charge and small atomic size of the combining elements. 
POLAR COVALENT BOND: The bond between two unlike atoms which differ 
in their affinities for electrons is said to be polar covalent bond. E.g. H-Cl  
COORDINATE BOND: The bond formed when one sided sharing of electrons 
take place is called a coordinate bond. Such a bond is also known as dative bond. It 
is represented by an arrow (?) pointing towards the acceptor atom. E.g. H
3N
?BF
3 
Bond Length: Bond length is defined as the equilibrium distance between the 
nuclei of two bonded atoms in a molecule 
Bond Angle: It is defined as the angle between the orbitals containing bonding 
electron pairs around the central atom in a molecule/complex ion 
Bond Enthalpy: It is defined as the amount of energy required to break one mole 
of  bonds of a particular type between two atoms in a gaseous state. 
Bond Order: In the Lewis description of covalent bond, the Bond Order is given 
by the number of bonds between the two atoms in a molecule 
Resonance:whenever a single Lewis structure cannot describe a molecule 
accurately, a number of structures with similar energy, positions of nuclei, bonding 
and non-bonding pairs of electrons are taken as the canonical structures of the 
hybrid which describes the molecule accurately 
Dipole moment : The product of the magnitude of the charge and the distance 
between the centres of positive and negative charge.It is a vector quantity and is 
represented by an arrow with its tail at the positive centre and head pointing towards 
a negative centre. Dipole moment ( µ) = charge (Q) × distance of separation (r) 
 
50 
 
SIGMA BOND: A covalent bond formed due to the overlapping of orbitals of the 
two atoms along the line joining the two nuclei (orbital axis) is called sigma (s) 
bond. For example, the bond formed due to s-s and s-p, p-p overlapping along the 
orbital axis are sigma bonds. 
Pi- BOND: A covalent bond formed by the side wise overlapping of p- or d- 
orbitals of two atoms is called as pi (p) bond. For example, the bond formed due to 
the sideways overlapping of the two p- orbitals is a pi- bond. 
HYDROGEN BOND: The bond between the hydrogen atom of one molecule and 
a more electro- negative element of same or another molecule is called as hydrogen 
bond. 
HYBRIDIZATION: The process of mixing of the atomic orbitals to form new 
hybrid orbitals is called hybridization. All hybrid orbitals of a particular kind have 
equal energy, identical shapes and are symmetrically oriented in shape. 
The hybrid orbitals are designed according to the type and the atomic orbitals 
merging together, e.g.,  
 
Molecu
le Type 
Shape 
Electron 
arrangeme
nt
†
 
     
Geometry
‡
 
Examples 
AX
2
E
0
 Linear 
 
 
 BeCl
2
, HgCl
2
, CO
2
 
AX
2
E
1
 Bent 
 
 
 NO
2
-
, SO
2
, O
3
, CCl
2
 
AX
2
E
2
 Bent 
 
 
 H
2
O, OF
2
 
AX
2
E
3
 Linear 
 
 
 XeF
2
, I
3
-
, XeCl
2
 
51 
 
AX
3
E
0
 
Trigonal 
planar 
 
 
 BF
3
, CO
3
2-
, NO
3
-
, SO
3
 
AX
3
E
1
 
Trigonal 
pyramidal 
 
 
 NH
3
, PCl
3
 
AX
3
E
2
 T-shaped 
 
 
 ClF
3
, BrF
3
 
AX
4
E
0
 
Tetrahedr
al 
 
 
 CH
4
, PO
4
3-
, SO
4
2-
, ClO
4
-
,  XeO
4
 
AX
4
E
1
 Seesaw 
 
 
 SF
4
 
AX
4
E
2
 
Square 
planar 
 
 
 XeF
4
 
AX
5
E
0
 
Trigonal 
bipyramid
al 
  
 PCl
5
 
AX
5
E
1
 
Square 
pyramidal 
 
 
 ClF
5
, BrF
5
, XeOF
4
 
AX
5
E
2
 
Pentagon
al planar 
 
  XeF
5
-