Chemical Bonding & Molecular Structure Class 11 Notes Chemistry Chapter 4

 Page 1


1. The interaction between two atoms which holds them together within a
molecule or ions in known as chemical bond.
2. The	 elements	 with	 one,	 two,	 three,	 four ,	 five,	 six	 or	 seven	 electrons	 is	 outer
shell, use these electrons to complete octet. The electrons which take part
in two or mo re	atoms	to	complete	octet	is	known	as	electrovalency .
3. Lewis	 symbols	 or	 electron	 dot	 symbols	 involve	 the	 presentation	 of	 valence
electrons (outer electrons) in an atom 
? ? ? ?
?
?
?
Na,Mg:,A ,Si
.
l
.
 etc.
4. E l e c t rova l e nt bond or ionic Bond : The bond (chemical interaction)
between	 two	 atoms	 formed	 by	 complete	 transference	 of	 electron	 from	
valence	 shell	 (outer	 shell)	 of	 an	 atom	 to	 another	 to	 complete	 octet	 is	 known	
as ionic bond.
5. This	 ionic	 bond	 is	 favoured	 by	 low	 ionization	 enthalpy	 of	 metal,	 high
electron	gain	enthalpy	of	non-metal	atom	and	high	lattice	enthalpy .
6. Characteristics	 of	 ionic	 compound	 :	 They	 are	 solids,	 a	 definite	 arrangement/
pattern	 of	 ion	 (to	 give	 crystalline	 solids),	 high	 melting	 point	 and	 boiling
point, conductors in fused state and in aqueous medium, soluble in H
2
O
[Hydration].
7. Lattice enthalpy : The	 ener gy	 released	 when	 one	 mole	 of	 ionic	 solid
is	 formed	 from	 its	 ions	 in	 their	 gaseous	 state.	 Lattice	 ener gy	 is	 directly
proportional	 to	 char ge	 of	 ion	 and	 inversely	 proportions	 to	 size	 of	 ions	i.e.,
more	is	char ge	density ,	more	is	lattice	enthalpy .
8. Mg —? Mg
2+ 
+ 2e
–
         O + 2e
– 
—? O
2–
    (2, 8, 2)                                (2, 6)
  Mg
2+
 + O
2–
 —?	MgO	Ionic	compound	[A 	crystalline	lattice].
Page 2


1. The interaction between two atoms which holds them together within a
molecule or ions in known as chemical bond.
2. The	 elements	 with	 one,	 two,	 three,	 four ,	 five,	 six	 or	 seven	 electrons	 is	 outer
shell, use these electrons to complete octet. The electrons which take part
in two or mo re	atoms	to	complete	octet	is	known	as	electrovalency .
3. Lewis	 symbols	 or	 electron	 dot	 symbols	 involve	 the	 presentation	 of	 valence
electrons (outer electrons) in an atom 
? ? ? ?
?
?
?
Na,Mg:,A ,Si
.
l
.
 etc.
4. E l e c t rova l e nt bond or ionic Bond : The bond (chemical interaction)
between	 two	 atoms	 formed	 by	 complete	 transference	 of	 electron	 from	
valence	 shell	 (outer	 shell)	 of	 an	 atom	 to	 another	 to	 complete	 octet	 is	 known	
as ionic bond.
5. This	 ionic	 bond	 is	 favoured	 by	 low	 ionization	 enthalpy	 of	 metal,	 high
electron	gain	enthalpy	of	non-metal	atom	and	high	lattice	enthalpy .
6. Characteristics	 of	 ionic	 compound	 :	 They	 are	 solids,	 a	 definite	 arrangement/
pattern	 of	 ion	 (to	 give	 crystalline	 solids),	 high	 melting	 point	 and	 boiling
point, conductors in fused state and in aqueous medium, soluble in H
2
O
[Hydration].
7. Lattice enthalpy : The	 ener gy	 released	 when	 one	 mole	 of	 ionic	 solid
is	 formed	 from	 its	 ions	 in	 their	 gaseous	 state.	 Lattice	 ener gy	 is	 directly
proportional	 to	 char ge	 of	 ion	 and	 inversely	 proportions	 to	 size	 of	 ions	i.e.,
more	is	char ge	density ,	more	is	lattice	enthalpy .
8. Mg —? Mg
2+ 
+ 2e
–
         O + 2e
– 
—? O
2–
    (2, 8, 2)                                (2, 6)
  Mg
2+
 + O
2–
 —?	MgO	Ionic	compound	[A 	crystalline	lattice].
9. (a) Born Haber	Cycle	:	For	formation	of	ionic	compound	e.g., Na
+
Cl
–
.
(b) Ionic bonds are Non directional in nature.
10. Fajan’s Rule : 	 Polariza bi l i t y 	 and 	 pol a ri z i ng 	 powe r . 	 T he	 powe r	 of	 a 	 c a t i on
to 	 distort	 the	 negative 	 field	 of	 an	 anion	 is	 called	 polari sing 	 power	 and	 the
tendency	 of 	 anion	 to	 get	 distorted	 its	 negative	 field	 by	 a	 cation	 is	 known
as	 polarizability . 	 Factors 	 affecting 	 polarizing 	 power 	 and 	 polarizability 	 are:
(a)	High	char ge	and	small 	size	of 	cation.
(b) 	High	char ge	and	lar ge	size 	of	anion.
11. Covalent Bond : Lewis Langmuir Concept
The	 (chemical	 interaction)	 bond	 formed	 by	 mutual	 sharing	 of	 electrons
between	 combining	 atom	 as	 to	 complete	 their 	 octets	 is 	 known	 as	 covalent
bond	and	no.	of	electrons 	involved 	is	called 	their	covalency .
12. Formal charge : [T otal	 no.	 of	 valence e
–
	 in	 free	 atom]	 –	 [T otal 	 no.	 of	 non
bonding	electrons] 	–	 [T otal	no.	of	shared	electrons]
13. The valence bond approach : (a) The two atomic orbitals with one
electron 	 each,	 overlap	 to	 give 	 maximum	 electron	 density	 region	 common
to	both 	atoms 	is	known	as	single	covalent	bond
(b) 	 The	 strength	 of	 covalent 	 bond	 is	 proportional	 to	 extent	 of	 overlapping	
between	the	atomic 	orbitals	of	valence shell.
14. Characteristics	 of	 covalent 	 compounds—(a) 	 They 	 are 	 in	 all 	 three	 physical
states solid, liquid, or gas depending upon factors like molecular mass,
van	der 	 W all's	force,	covalency ,	Hydrogen	bonding, 	polarity	etc.
Page 3


1. The interaction between two atoms which holds them together within a
molecule or ions in known as chemical bond.
2. The	 elements	 with	 one,	 two,	 three,	 four ,	 five,	 six	 or	 seven	 electrons	 is	 outer
shell, use these electrons to complete octet. The electrons which take part
in two or mo re	atoms	to	complete	octet	is	known	as	electrovalency .
3. Lewis	 symbols	 or	 electron	 dot	 symbols	 involve	 the	 presentation	 of	 valence
electrons (outer electrons) in an atom 
? ? ? ?
?
?
?
Na,Mg:,A ,Si
.
l
.
 etc.
4. E l e c t rova l e nt bond or ionic Bond : The bond (chemical interaction)
between	 two	 atoms	 formed	 by	 complete	 transference	 of	 electron	 from	
valence	 shell	 (outer	 shell)	 of	 an	 atom	 to	 another	 to	 complete	 octet	 is	 known	
as ionic bond.
5. This	 ionic	 bond	 is	 favoured	 by	 low	 ionization	 enthalpy	 of	 metal,	 high
electron	gain	enthalpy	of	non-metal	atom	and	high	lattice	enthalpy .
6. Characteristics	 of	 ionic	 compound	 :	 They	 are	 solids,	 a	 definite	 arrangement/
pattern	 of	 ion	 (to	 give	 crystalline	 solids),	 high	 melting	 point	 and	 boiling
point, conductors in fused state and in aqueous medium, soluble in H
2
O
[Hydration].
7. Lattice enthalpy : The	 ener gy	 released	 when	 one	 mole	 of	 ionic	 solid
is	 formed	 from	 its	 ions	 in	 their	 gaseous	 state.	 Lattice	 ener gy	 is	 directly
proportional	 to	 char ge	 of	 ion	 and	 inversely	 proportions	 to	 size	 of	 ions	i.e.,
more	is	char ge	density ,	more	is	lattice	enthalpy .
8. Mg —? Mg
2+ 
+ 2e
–
         O + 2e
– 
—? O
2–
    (2, 8, 2)                                (2, 6)
  Mg
2+
 + O
2–
 —?	MgO	Ionic	compound	[A 	crystalline	lattice].
9. (a) Born Haber	Cycle	:	For	formation	of	ionic	compound	e.g., Na
+
Cl
–
.
(b) Ionic bonds are Non directional in nature.
10. Fajan’s Rule : 	 Polariza bi l i t y 	 and 	 pol a ri z i ng 	 powe r . 	 T he	 powe r	 of	 a 	 c a t i on
to 	 distort	 the	 negative 	 field	 of	 an	 anion	 is	 called	 polari sing 	 power	 and	 the
tendency	 of 	 anion	 to	 get	 distorted	 its	 negative	 field	 by	 a	 cation	 is	 known
as	 polarizability . 	 Factors 	 affecting 	 polarizing 	 power 	 and 	 polarizability 	 are:
(a)	High	char ge	and	small 	size	of 	cation.
(b) 	High	char ge	and	lar ge	size 	of	anion.
11. Covalent Bond : Lewis Langmuir Concept
The	 (chemical	 interaction)	 bond	 formed	 by	 mutual	 sharing	 of	 electrons
between	 combining	 atom	 as	 to	 complete	 their 	 octets	 is 	 known	 as	 covalent
bond	and	no.	of	electrons 	involved 	is	called 	their	covalency .
12. Formal charge : [T otal	 no.	 of	 valence e
–
	 in	 free	 atom]	 –	 [T otal 	 no.	 of	 non
bonding	electrons] 	–	 [T otal	no.	of	shared	electrons]
13. The valence bond approach : (a) The two atomic orbitals with one
electron 	 each,	 overlap	 to	 give 	 maximum	 electron	 density	 region	 common
to	both 	atoms 	is	known	as	single	covalent	bond
(b) 	 The	 strength	 of	 covalent 	 bond	 is	 proportional	 to	 extent	 of	 overlapping	
between	the	atomic 	orbitals	of	valence shell.
14. Characteristics	 of	 covalent 	 compounds—(a) 	 They 	 are 	 in	 all 	 three	 physical
states solid, liquid, or gas depending upon factors like molecular mass,
van	der 	 W all's	force,	covalency ,	Hydrogen	bonding, 	polarity	etc.
(b) 	 These	 are	 direct ional, 	 soluble	 in	 less	 polar	 or	 non-polar 	 solvents,	 less	
melting point and boiling point 	 [than	 ionic	 compounds]	 due	 to	 weak	 van	
der -W aal	forces,	bad	or	good	conductor	of	electricity .
15. Hybridization : 	 (a)	 Phenomenon	 of	 interm ixing	 of	 atomic	 orbitals	 with
slightly 	 different 	 ener gies 	 to 	 form 	 new	 orbitals	 of	 equal 	 ener gy 	 and 	 identical
shape. The new orbitals are knows as hybrid orbitals.
(b) 	 The	 number	 of	 hybrid	 orbitals 	 is	 equal	 to	 number	 of	 atomic	 orbitals
mixing.
(c) As the ‘s ’ 	 character	 in	 hybrid	 orbita l	 increases,	 electronegativity	 and
size 	of	hybrid	orbital	increases.
16. VSEPR (Valence shell electron pair repulsion theory):-
(a)	 There	 are	 three 	 types	 of	 repulsion	 in	 a	 covalent	 molecule lp - lp >
lp - bp > bp - bp.
(b) 	 These	 repulsion 	 depend	 upon	 difference 	 in	 electronegativity 	 between
combining atom.
17. Sigma and Pi p bond : 	 (a)	 The	 bond	 formed	 by	 overlap	 of	 two	 atomic
orbitals	along	the	internuclear 	axis	of	two	atoms 	is	Sigma	bonds.
Extent		of	overlap 	is	large therefore strong bond.
(b) p bond : 	 The	 bond 	 formed	 by 	 sideways 	 overlap	 of	 two	 atomic 	 orbitals,
extent 	 of	 overlap 	 is	 not	 along	 the	 nuclear	 axis	 therefore	 it	 is	 a	 weak	 bond.
(c) A single bond contains s bond; A double bond is one s and one p bond
a	triple	covalent 	bond	contains 	one	s and 2p bonds.
18. Resonance : 	 (a) 	 The	 delocalization	 of	 electron s	 in	 a	 molecule/ion	 which
results	 in	 observed	 bond	 length, 	 bond	 order ,	 bond	 ener gy	 different 	 from
normal 	 covalent 	 bond	 data	 is	 known	 as	 resonance. 	 V arious 	 resonating
structures 	have	nearly 	same	ener gy 	and	interconvertible 	to	each 	other .
(b) 	 It	 gives 	 stability 	 to	 the 	 molecule/ion. 	 Atom 	 do 	 not 	 shift 	 their 	 position 	 in
any 	 of	 the	 res onating 	 s tructure.	 The	 s tructure	 w hich 	 is 	 near to all resonating
structure 	 and	 nearly 	 explain	 the	 property 	 of	 that	 molecule/ion	 is	 known
Page 4


1. The interaction between two atoms which holds them together within a
molecule or ions in known as chemical bond.
2. The	 elements	 with	 one,	 two,	 three,	 four ,	 five,	 six	 or	 seven	 electrons	 is	 outer
shell, use these electrons to complete octet. The electrons which take part
in two or mo re	atoms	to	complete	octet	is	known	as	electrovalency .
3. Lewis	 symbols	 or	 electron	 dot	 symbols	 involve	 the	 presentation	 of	 valence
electrons (outer electrons) in an atom 
? ? ? ?
?
?
?
Na,Mg:,A ,Si
.
l
.
 etc.
4. E l e c t rova l e nt bond or ionic Bond : The bond (chemical interaction)
between	 two	 atoms	 formed	 by	 complete	 transference	 of	 electron	 from	
valence	 shell	 (outer	 shell)	 of	 an	 atom	 to	 another	 to	 complete	 octet	 is	 known	
as ionic bond.
5. This	 ionic	 bond	 is	 favoured	 by	 low	 ionization	 enthalpy	 of	 metal,	 high
electron	gain	enthalpy	of	non-metal	atom	and	high	lattice	enthalpy .
6. Characteristics	 of	 ionic	 compound	 :	 They	 are	 solids,	 a	 definite	 arrangement/
pattern	 of	 ion	 (to	 give	 crystalline	 solids),	 high	 melting	 point	 and	 boiling
point, conductors in fused state and in aqueous medium, soluble in H
2
O
[Hydration].
7. Lattice enthalpy : The	 ener gy	 released	 when	 one	 mole	 of	 ionic	 solid
is	 formed	 from	 its	 ions	 in	 their	 gaseous	 state.	 Lattice	 ener gy	 is	 directly
proportional	 to	 char ge	 of	 ion	 and	 inversely	 proportions	 to	 size	 of	 ions	i.e.,
more	is	char ge	density ,	more	is	lattice	enthalpy .
8. Mg —? Mg
2+ 
+ 2e
–
         O + 2e
– 
—? O
2–
    (2, 8, 2)                                (2, 6)
  Mg
2+
 + O
2–
 —?	MgO	Ionic	compound	[A 	crystalline	lattice].
9. (a) Born Haber	Cycle	:	For	formation	of	ionic	compound	e.g., Na
+
Cl
–
.
(b) Ionic bonds are Non directional in nature.
10. Fajan’s Rule : 	 Polariza bi l i t y 	 and 	 pol a ri z i ng 	 powe r . 	 T he	 powe r	 of	 a 	 c a t i on
to 	 distort	 the	 negative 	 field	 of	 an	 anion	 is	 called	 polari sing 	 power	 and	 the
tendency	 of 	 anion	 to	 get	 distorted	 its	 negative	 field	 by	 a	 cation	 is	 known
as	 polarizability . 	 Factors 	 affecting 	 polarizing 	 power 	 and 	 polarizability 	 are:
(a)	High	char ge	and	small 	size	of 	cation.
(b) 	High	char ge	and	lar ge	size 	of	anion.
11. Covalent Bond : Lewis Langmuir Concept
The	 (chemical	 interaction)	 bond	 formed	 by	 mutual	 sharing	 of	 electrons
between	 combining	 atom	 as	 to	 complete	 their 	 octets	 is 	 known	 as	 covalent
bond	and	no.	of	electrons 	involved 	is	called 	their	covalency .
12. Formal charge : [T otal	 no.	 of	 valence e
–
	 in	 free	 atom]	 –	 [T otal 	 no.	 of	 non
bonding	electrons] 	–	 [T otal	no.	of	shared	electrons]
13. The valence bond approach : (a) The two atomic orbitals with one
electron 	 each,	 overlap	 to	 give 	 maximum	 electron	 density	 region	 common
to	both 	atoms 	is	known	as	single	covalent	bond
(b) 	 The	 strength	 of	 covalent 	 bond	 is	 proportional	 to	 extent	 of	 overlapping	
between	the	atomic 	orbitals	of	valence shell.
14. Characteristics	 of	 covalent 	 compounds—(a) 	 They 	 are 	 in	 all 	 three	 physical
states solid, liquid, or gas depending upon factors like molecular mass,
van	der 	 W all's	force,	covalency ,	Hydrogen	bonding, 	polarity	etc.
(b) 	 These	 are	 direct ional, 	 soluble	 in	 less	 polar	 or	 non-polar 	 solvents,	 less	
melting point and boiling point 	 [than	 ionic	 compounds]	 due	 to	 weak	 van	
der -W aal	forces,	bad	or	good	conductor	of	electricity .
15. Hybridization : 	 (a)	 Phenomenon	 of	 interm ixing	 of	 atomic	 orbitals	 with
slightly 	 different 	 ener gies 	 to 	 form 	 new	 orbitals	 of	 equal 	 ener gy 	 and 	 identical
shape. The new orbitals are knows as hybrid orbitals.
(b) 	 The	 number	 of	 hybrid	 orbitals 	 is	 equal	 to	 number	 of	 atomic	 orbitals
mixing.
(c) As the ‘s ’ 	 character	 in	 hybrid	 orbita l	 increases,	 electronegativity	 and
size 	of	hybrid	orbital	increases.
16. VSEPR (Valence shell electron pair repulsion theory):-
(a)	 There	 are	 three 	 types	 of	 repulsion	 in	 a	 covalent	 molecule lp - lp >
lp - bp > bp - bp.
(b) 	 These	 repulsion 	 depend	 upon	 difference 	 in	 electronegativity 	 between
combining atom.
17. Sigma and Pi p bond : 	 (a)	 The	 bond	 formed	 by	 overlap	 of	 two	 atomic
orbitals	along	the	internuclear 	axis	of	two	atoms 	is	Sigma	bonds.
Extent		of	overlap 	is	large therefore strong bond.
(b) p bond : 	 The	 bond 	 formed	 by 	 sideways 	 overlap	 of	 two	 atomic 	 orbitals,
extent 	 of	 overlap 	 is	 not	 along	 the	 nuclear	 axis	 therefore	 it	 is	 a	 weak	 bond.
(c) A single bond contains s bond; A double bond is one s and one p bond
a	triple	covalent 	bond	contains 	one	s and 2p bonds.
18. Resonance : 	 (a) 	 The	 delocalization	 of	 electron s	 in	 a	 molecule/ion	 which
results	 in	 observed	 bond	 length, 	 bond	 order ,	 bond	 ener gy	 different 	 from
normal 	 covalent 	 bond	 data	 is	 known	 as	 resonance. 	 V arious 	 resonating
structures 	have	nearly 	same	ener gy 	and	interconvertible 	to	each 	other .
(b) 	 It	 gives 	 stability 	 to	 the 	 molecule/ion. 	 Atom 	 do 	 not 	 shift 	 their 	 position 	 in
any 	 of	 the	 res onating 	 s tructure.	 The	 s tructure	 w hich 	 is 	 near to all resonating
structure 	 and	 nearly 	 explain	 the	 property 	 of	 that	 molecule/ion	 is	 known
44
as resonating hybrid. 
19. Dipole moment ( µ) : (a) 	 For 	 polar	 covalent	 molecules 	 (atoms 	 with
difference	 in	 electronegativity]	 the	 product 	 of	 char ge	 present	 on	 either
atom	 and	 distance	 b/w	 them	 is	 known	 as	 dipole	 moment.	 (b) 	 Being	 vector
quantity , 	 if	 net	 resultant 	 of	 all 	 vector	 is	 zero	 the 	 molecule	 has	 zero	 dipole
moment and known as non polar molecule.
20. Hydrogen bonding : 	 The	 electrostatic	 interac tion	 b/w	 molecules 	 when
H	is	bonded	with	highly 	electronegtive	atoms	(F , 	O,	N	only).
(a) Intramolecular Hydrogen bonding : Hydrogen
bonding with in a molecule.
(b) Intermolecular hydrogen bonding : 	 When
hydrogen 	 bonding 	 is	 present 	 between 	 two 	 same	 or
different	molecules.
21. Molecular orbital theory :	 (a)	 The	 overlap	 of	 atomic	 orbitals	 of	 same
symmetry	 of	 two	 homonuclear	 atoms	 to	 give 	 addition	 or	 subtraction	 of
wave	 functions	 and	 form	 bonding	 MO	 and	 antibonding 	 MO	 	 respectively
is 	known	as 	MO	theory .
(b) The e
–
	 are	 filled 	 in	 molecular	 orbitals 	 in	 their 	 increasing	 order	 ot	 their
energies in a molecule.
(c) Bond order :
= 
No. of electron in BMO – No. of electrons in ABMO
2
]
2–
Non-polar
Page 5


1. The interaction between two atoms which holds them together within a
molecule or ions in known as chemical bond.
2. The	 elements	 with	 one,	 two,	 three,	 four ,	 five,	 six	 or	 seven	 electrons	 is	 outer
shell, use these electrons to complete octet. The electrons which take part
in two or mo re	atoms	to	complete	octet	is	known	as	electrovalency .
3. Lewis	 symbols	 or	 electron	 dot	 symbols	 involve	 the	 presentation	 of	 valence
electrons (outer electrons) in an atom 
? ? ? ?
?
?
?
Na,Mg:,A ,Si
.
l
.
 etc.
4. E l e c t rova l e nt bond or ionic Bond : The bond (chemical interaction)
between	 two	 atoms	 formed	 by	 complete	 transference	 of	 electron	 from	
valence	 shell	 (outer	 shell)	 of	 an	 atom	 to	 another	 to	 complete	 octet	 is	 known	
as ionic bond.
5. This	 ionic	 bond	 is	 favoured	 by	 low	 ionization	 enthalpy	 of	 metal,	 high
electron	gain	enthalpy	of	non-metal	atom	and	high	lattice	enthalpy .
6. Characteristics	 of	 ionic	 compound	 :	 They	 are	 solids,	 a	 definite	 arrangement/
pattern	 of	 ion	 (to	 give	 crystalline	 solids),	 high	 melting	 point	 and	 boiling
point, conductors in fused state and in aqueous medium, soluble in H
2
O
[Hydration].
7. Lattice enthalpy : The	 ener gy	 released	 when	 one	 mole	 of	 ionic	 solid
is	 formed	 from	 its	 ions	 in	 their	 gaseous	 state.	 Lattice	 ener gy	 is	 directly
proportional	 to	 char ge	 of	 ion	 and	 inversely	 proportions	 to	 size	 of	 ions	i.e.,
more	is	char ge	density ,	more	is	lattice	enthalpy .
8. Mg —? Mg
2+ 
+ 2e
–
         O + 2e
– 
—? O
2–
    (2, 8, 2)                                (2, 6)
  Mg
2+
 + O
2–
 —?	MgO	Ionic	compound	[A 	crystalline	lattice].
9. (a) Born Haber	Cycle	:	For	formation	of	ionic	compound	e.g., Na
+
Cl
–
.
(b) Ionic bonds are Non directional in nature.
10. Fajan’s Rule : 	 Polariza bi l i t y 	 and 	 pol a ri z i ng 	 powe r . 	 T he	 powe r	 of	 a 	 c a t i on
to 	 distort	 the	 negative 	 field	 of	 an	 anion	 is	 called	 polari sing 	 power	 and	 the
tendency	 of 	 anion	 to	 get	 distorted	 its	 negative	 field	 by	 a	 cation	 is	 known
as	 polarizability . 	 Factors 	 affecting 	 polarizing 	 power 	 and 	 polarizability 	 are:
(a)	High	char ge	and	small 	size	of 	cation.
(b) 	High	char ge	and	lar ge	size 	of	anion.
11. Covalent Bond : Lewis Langmuir Concept
The	 (chemical	 interaction)	 bond	 formed	 by	 mutual	 sharing	 of	 electrons
between	 combining	 atom	 as	 to	 complete	 their 	 octets	 is 	 known	 as	 covalent
bond	and	no.	of	electrons 	involved 	is	called 	their	covalency .
12. Formal charge : [T otal	 no.	 of	 valence e
–
	 in	 free	 atom]	 –	 [T otal 	 no.	 of	 non
bonding	electrons] 	–	 [T otal	no.	of	shared	electrons]
13. The valence bond approach : (a) The two atomic orbitals with one
electron 	 each,	 overlap	 to	 give 	 maximum	 electron	 density	 region	 common
to	both 	atoms 	is	known	as	single	covalent	bond
(b) 	 The	 strength	 of	 covalent 	 bond	 is	 proportional	 to	 extent	 of	 overlapping	
between	the	atomic 	orbitals	of	valence shell.
14. Characteristics	 of	 covalent 	 compounds—(a) 	 They 	 are 	 in	 all 	 three	 physical
states solid, liquid, or gas depending upon factors like molecular mass,
van	der 	 W all's	force,	covalency ,	Hydrogen	bonding, 	polarity	etc.
(b) 	 These	 are	 direct ional, 	 soluble	 in	 less	 polar	 or	 non-polar 	 solvents,	 less	
melting point and boiling point 	 [than	 ionic	 compounds]	 due	 to	 weak	 van	
der -W aal	forces,	bad	or	good	conductor	of	electricity .
15. Hybridization : 	 (a)	 Phenomenon	 of	 interm ixing	 of	 atomic	 orbitals	 with
slightly 	 different 	 ener gies 	 to 	 form 	 new	 orbitals	 of	 equal 	 ener gy 	 and 	 identical
shape. The new orbitals are knows as hybrid orbitals.
(b) 	 The	 number	 of	 hybrid	 orbitals 	 is	 equal	 to	 number	 of	 atomic	 orbitals
mixing.
(c) As the ‘s ’ 	 character	 in	 hybrid	 orbita l	 increases,	 electronegativity	 and
size 	of	hybrid	orbital	increases.
16. VSEPR (Valence shell electron pair repulsion theory):-
(a)	 There	 are	 three 	 types	 of	 repulsion	 in	 a	 covalent	 molecule lp - lp >
lp - bp > bp - bp.
(b) 	 These	 repulsion 	 depend	 upon	 difference 	 in	 electronegativity 	 between
combining atom.
17. Sigma and Pi p bond : 	 (a)	 The	 bond	 formed	 by	 overlap	 of	 two	 atomic
orbitals	along	the	internuclear 	axis	of	two	atoms 	is	Sigma	bonds.
Extent		of	overlap 	is	large therefore strong bond.
(b) p bond : 	 The	 bond 	 formed	 by 	 sideways 	 overlap	 of	 two	 atomic 	 orbitals,
extent 	 of	 overlap 	 is	 not	 along	 the	 nuclear	 axis	 therefore	 it	 is	 a	 weak	 bond.
(c) A single bond contains s bond; A double bond is one s and one p bond
a	triple	covalent 	bond	contains 	one	s and 2p bonds.
18. Resonance : 	 (a) 	 The	 delocalization	 of	 electron s	 in	 a	 molecule/ion	 which
results	 in	 observed	 bond	 length, 	 bond	 order ,	 bond	 ener gy	 different 	 from
normal 	 covalent 	 bond	 data	 is	 known	 as	 resonance. 	 V arious 	 resonating
structures 	have	nearly 	same	ener gy 	and	interconvertible 	to	each 	other .
(b) 	 It	 gives 	 stability 	 to	 the 	 molecule/ion. 	 Atom 	 do 	 not 	 shift 	 their 	 position 	 in
any 	 of	 the	 res onating 	 s tructure.	 The	 s tructure	 w hich 	 is 	 near to all resonating
structure 	 and	 nearly 	 explain	 the	 property 	 of	 that	 molecule/ion	 is	 known
44
as resonating hybrid. 
19. Dipole moment ( µ) : (a) 	 For 	 polar	 covalent	 molecules 	 (atoms 	 with
difference	 in	 electronegativity]	 the	 product 	 of	 char ge	 present	 on	 either
atom	 and	 distance	 b/w	 them	 is	 known	 as	 dipole	 moment.	 (b) 	 Being	 vector
quantity , 	 if	 net	 resultant 	 of	 all 	 vector	 is	 zero	 the 	 molecule	 has	 zero	 dipole
moment and known as non polar molecule.
20. Hydrogen bonding : 	 The	 electrostatic	 interac tion	 b/w	 molecules 	 when
H	is	bonded	with	highly 	electronegtive	atoms	(F , 	O,	N	only).
(a) Intramolecular Hydrogen bonding : Hydrogen
bonding with in a molecule.
(b) Intermolecular hydrogen bonding : 	 When
hydrogen 	 bonding 	 is	 present 	 between 	 two 	 same	 or
different	molecules.
21. Molecular orbital theory :	 (a)	 The	 overlap	 of	 atomic	 orbitals	 of	 same
symmetry	 of	 two	 homonuclear	 atoms	 to	 give 	 addition	 or	 subtraction	 of
wave	 functions	 and	 form	 bonding	 MO	 and	 antibonding 	 MO	 	 respectively
is 	known	as 	MO	theory .
(b) The e
–
	 are	 filled 	 in	 molecular	 orbitals 	 in	 their 	 increasing	 order	 ot	 their
energies in a molecule.
(c) Bond order :
= 
No. of electron in BMO – No. of electrons in ABMO
2
]
2–
Non-polar
45
(d) 	 More	 is	 bond	 order 	 more	 is	 bond	 ener gy 	 lesser 	 is	 the	 bond	 length.	 If	
bond	order 	zero 	then	molecule/molecular 	ion	do	not	exist.
(e)	Increasing 	order	of	ener gy	of	MO	for	upto	14e
–
	(For	B
2
, C
2
 and N
2
).
**
12
1 2 2 22
,, , , , ss
s s px py pz
ss s s p p s =
, 
for other molecules
 
? 
* * **
1 2 22
1 2 22 2 2
,, , , , , , s s px py
s s pz px py pz
ss s s s p p p p s ==
(d)	 This	theory	also 	decides 	the 	magnetic	behaviour	of	molecules.
22. Coordinate covalent bond : 	 The	 sigma	 bond	 formed 	 by	 donation	 of	 lp
into 	 vacant	 unhybridised 	 orbital	 of	 other	 atom	 (acception	 atom)	 is 	 known
as	coordinte	covalent 	bond	or	donor acceptor or dative bond.
H
3
N ? 	BF
3
23. Bond strength; Bond energy; Bond length :
For	covalent	molecule 		 Bond	Enthalpy	: C = C > C = C > C — C
Bond Length    : C = C < C = C < C — C
Bond angles : (a) As the no. of lp increase; bp – lp, lp – lp repulsion 
increase therefore bond angles decrease.
(b) As lp decreases bond angle increases.
Important Points :
24. (a)	 Maximum 	 density	 of	 H
2
O	 at	 4°C	 due	 to	 extensive.	 Intermolecular
hydrogen	bonding.
(b) H
2
O to H
2
S	bond	angle 	decrease
(c) NH
3
 more µ	than	NF
3
.
(d) NCl
3
 more µ	than	NF
3
.
25. Van der waal forces weak intermolecular force of attraction.
(a) Dipole dipole interactions there which are present between polar
molecules.
(b) Dipole induced dipole interactions. Those which are present polar
between and non polar molecules.
**
p ==
**
22
2 2
, , px py
pz
p p s ==
**
,p ==