chemical bonding class 11 notes for neb board.pdf

Notes

1. Chemical Bonding and Shape of Molecules
Chemical Bond:The force of attraction which binds the atoms, ions or molecules
together is called chemical bond.
Valence shell: The outermost shell of an atom is called valance shell.
Valence electron:The electrons in outermost shell of an atom is called valance
electrons.
Lewis symbols: The outer shell electrons are shown as dots(or cross) surrounding
the symbol of the atom. These symbols are known as Lewis symbols.
The concept of Lewis symbols was introduced by G. N. Lewis

2. Lewis Dot Symbols for 1-20 elements

3. Octet rule :
The tendency of the atoms to acquire eight electrons in their outermost shell by
gaining, losing or sharing of electrons is known as octet rule.
Limitation of octet rule :
•Octet rule is violated for the compounds containing hydrogen atom. Eg.H
2O,
NH
3, H
2SO
4etc.
•It could not explain the formation electron deficient molecules such as BeCl
2,
BF
3, AlCl
3etc.
•It could not explain about the excess electron of phosphorus atom in PCl
5,
SF
6, IF
7 etc.

4. Types of chemical bond :
Electrovalent bond or ionic bond:
The bond formed by the complete transfer of electron from one combining atom to
the valence shell of another combining atom is called electrovalent bond.
The no. of electrons lost or gained during the formation of electrovalent bond is
termed as electrovalencyof the element.
This type of bond is formed when the combining atoms have large difference in
electronegativity. The compound formed through ionic bond is called
electrovalent or ionic compound.

5. Characteristics of ionic compound:
Ionic compound have following characteristics.
1.Ionic compound are generally crystalline in nature.
2. They are soluble in water and other polar solvent but insoluble in non polar
solvent like benzene.
3. Ionic compound do not conduct the electricity at solid state. However, They are
able to conduct the electricity in the molten state or in aqueous solution.
4. They are hard but brittle in nature.
5. Ionic compound have high melting and boiling point. Since electrovalent bond is
very strong bond so large amount of heat is required to break the bond.
6. The density of ionic compound is higher due to the presence of strong
electrostatic force of attraction between the cations and anions.

6. Eg.of ionic compounds:
NaCl, CaF
2, MgS, Na
2S, MgCl
2, CaO, etc.
Formation of ionic compound (Lewis symbols) :
i)Formation of sodium chloride
NaCl is formed by complete transfer of one electron from valence shell of sodium
to valence shell of chlorine.
Na
×
+ ̇Cl ̤̈꞉ Na
+
+ Cl
-
(2,8,1) (2,8,7) (2,8) (2,8,8)
[Na
+
][Cl
-
]

7. Covalent Bond:
The bond formed by mutual sharing of one or more valance electrons between the
combining atoms of same or different elements having similar electronegativity is
called covalent bond. The number of electron shared by an atom during the
formation of covalent bond is called covalency . The compounds formed by
formation of covalent bond are called covalent compounds. e.g. CH
4, C
2H
6, H
2O
etc.
Characteristics of covalent compound:
The covalent compound have following characteristics.
1.Covalent compound exist in solid, liquid and gaseous state.
2. They have low melting and boiling point value and are insoluble in water but
soluble in nonpolar solvent, Like benzene.

8. 3. They do not conduct the electricity.
4. The reaction of covalent compounds are slow than that of ionic compound.
Eg.of covalent compounds:
H
2, O
2, N
2, H
2O, CH
4, HF, H
2S, HCN,C
2H
2,NH
3, CH
3OH, CCl
4, H
2O
2,
CO
2,CHCl
3.
Lewis structure of some covalent compound:
i) Formation of H
2molecule
Hydrogen molecule is formed by sharing of one-one electron of each atom of
hydrogen in which both atoms form their duplet.
H×+ ×H H
2

9. Coordinate Covalent Bond Or Dative Bond:
The bond formed when one-sided sharing of electron pair takes place is called a
coordinate covalent bond. Such bond is known as dative bond. The atom which
provides the electron pair is termed as the donor atom while the other atom which
accept it is termed as acceptor. A coordinate covalent bond is represented by an
arrow (→) pointing towards the acceptor atom. The resulting compounds are
known as coordinate covalent compound.
Characteristics of Coordinate Covalent Compound :
1.They are generally exist in liquid and gaseous state.
2. They are sparingly soluble in water and organic solvent due to semi ionic in
nature.
3. The melting point and boiling point of coordinate covalent compound is lower
than covalent compound .

10. Lewis structures of some coordinate covalent compounds:
i)Formation of O
3ii) Formation of N
2O
O = O → O N ≡ N → O
iii) Formation of SO
2iv) Formation of CO
O = S → O O = C
v) Formation of SO
3vi) Formation of N
2O
4
O O O
↑ ↑ ↑
O = S → O O = N –N = O
vii) Formation of P
2O
5viii) Formation of HNO
3
O O O
↑ ↑ ↑
O = P –O –P = O H -O –N =O

11. ix) Formation of H
2SO
4x) Formation H
3PO
4
O O
↑ ↑
H –O –S –O –H H –O –P –O –H
↓ │
O O –H
xi) Formation of HClO (Hypochlorus acid)
H –Cl → O
xii) Formation of H
2SO
3(Sulphurous acid)
O
↑
H –O –S –O –H O
xiii) Formation of H
2CO
3 ‖
(Carbonic acid) H –O –C –O –H

12. 14) Formation of HNO
2(Nitrous acid)
O
↑
H –N = O
15) Formation of H
3O
+
H
|
H –O → H
+
16) Formation of SO4
--
O
↑
-
O –S –O
-
↓
O

13. 17) Formation of fluoroborate ion (BF
4
-
)
F
│
F –B ← F
-
│
F
18) Formation of NH
4Cl
H
│
[ H –N → H
+
] + Cl
-
│
H

14. Hydrogen Bond :
When hydrogen atom is bonded with highly electronegative element such as F, O,
N then the shared pair of electron lies more towards the electronegative element.
Hence partial positive and negative charge generate i.e. molecule becomes polar.
The bond between the hydrogen atom of one molecule and a more
electronegative atom of the same or another molecule is called hydrogen bond.
It is shown by dotted line (……….) .
Condition for formation of hydrogen bond:
1.The element link with hydrogen atom in molecule should be highly negative
(Like F,O,N).
2. The atom of the highly electronegative element should be small.

15. Types of Hydrogen Bond :
Intermolecular hydrogen bond :
The hydrogen bonding between the H-atom of one molecule and an atom of
electronegative element of another molecule is called intermolecular hydrogen
bond. For example hydrogen bonding in water, ammonia etc.
H –O ……H –O……..H –O ….. H –O
| | | |
H H H H
Intramolecular hydrogen bond :
The hydrogen bonding between the hydrogen atom and more electronegative
atom within the molecule is called intramolecular hydrogen bond. For example
hydrogen bonding in o-nitrophenol, salicylic acid etc.

16. Application of hydrogen bond:
i)Solubility of covalent compound : covalent compound generally insoluble
in water. However the covalent compound which can form the hydrogen
bond with water readily dissolve in it.
ii)Physical state: Hydrogen bonding affects the physical state of a substance.
For example H
2O is liquid while H
2S gas at room temperature.
iii)Increase in melting and boiling point : Stronger the hydrogen bonding
greater will be the intermolecular force of attraction so large amount of heat
is required for breaking the bond. Thus m.p. and b.p. of hydrogen bonded
compound becomes high.

17. MetallicBond:
Metallicbondappearsinmetalandsomealloys.The
bondinginmetalwasfirstexplainedbyDrudeand
Lorentz.Accordingtothemmetalconsistof
positivelychargedmetallicions(kernal)andvalence
electronsaremovingbetweentheionslikegas
molecule.sothisisalsocalledelectronseamodel.
Thesimultaneousforceofattractionbetweenthe
mobileelectronandpositivechargedionwhich
bindsthemetalatomstogetherisknownas
metallicbond.
Inmetal,valenceelectronsarenotcompletelybound
andtheyaremobile.Duetothis,metalsaregood
conductorofelectricity.

18. Metalshavefollowingspecificproperties,
whichareduetometallicbond:
a)Metalsaregoodconductorofelectricity.
b)Metalsaremalleableandductile.
c)Metalshavelustre.
Inmetalliccrystal,therearefreeelectrons.
Thefreeelectronsallowacurrenttoflow
throughmetalliccrystals.Whenanegative
chargeisappliedatoneend,itmoves
towardstheotherend.So,Metalsaregood
conductorofelectricity.
Duetometallicbonding,metal
atomshaveabilitytoshiftinto
newpositionswithoutbreaking
thebond.Ifasmallstressisput
ontothemetal,thelayersofatoms
willstarttorollovereachother.It
isthereasonformalleabilityand
ductilityofmetals.
Theoutermostelectronsin
metalscanmovefreelyin
themetalcausinganylight
incidentonthemtoget
reflectedback.Duetothis
reflection,metalsurface
appearsshinyorlustrous.

19. VanderWaal’sforceofattraction:
DutchchemistVanderwaalProposedthatthereisaforceofattractionbetween
thenon-polarmolecule.ThisforceiscalledVanderwaalforce.Itcanbe
imaginatedthatduetorapidmovementofelectron,theelectrondistributionof
atommaybeunsymmetricalwithslightincreaseinelectrondensityinoneside
whichdevelopsthepositiveandnegativeendataparticularinstant.i.e.a
temporarydipoleisformed.Suchdipoleiscalledinstantaneousdipoleandwhich
developstheinduceddipoletoanotheratomneartoit.
The attractive forces between the instantaneous dipoles and induced dipoles
are called Vander Waal forces or London forces.

20. Classification of crystalline solid:
Crystalline solids are classified on the basis of nature of bonding which are given
as:
i)Ionic Solid :
The solid in which the crystals are formed from ions and they are held together
in crystal lattice by strong electrostatic force of attraction is called ionic solid.
They have high melting and boiling point and conduct the electricity in
aqueous solution. e.g. NaCl, KCl, CaCl
2etc.
ii)Metallic Solid :
The solids in which structural units are metal atom and they are bonded with
each other by metallic bond are called metallic solid. They are good conductor
of electricity. e.g. iron, silver, copper etc.
iii)Molecular solids :
The solids in which structural unit are molecules and

21. molecules in crystal lattice are held together by very weak Vander waal force are
called molecular solids. e.g. iodine, camphor, solid carbon dioxide etc.
iv) Covalent Solids :
The solid in which structural units are atoms and they are combined together by
covalent bond between them are called covalent solids. e.g. diamond, graphite
etc.
Resonance :
There are some molecules which can represented by more then one lewis
structure due to delocalization of non bonded electrons or pie-electrons. Such
lewis structure are called resonating structure and phenomenon is called
resonance. In other word resonance can be defined as the electronic effect which
is arises due to delocalization of pie electron.

22. The actual structure is regarded as a combination of these
various structures which is called resonance hybrid and it is the most stable form.
Resonating structure of some molecules :
i)Ozone (O
3)
[ O = O → O ↔ O ← O = O] ≡ O –O –O
ii) Sulphur trioxide (SO
3)
O O O O
↑ ‖ ↑ │
[O ← S = O ↔ O←S→O ↔ O = S→O] ≡ O –S –O
iii) Sulphur dioxide (SO
2)
[O = S → O ↔ O ← S = O] ≡ O –S –O

23. iv) Carbonate ion (CO
3
--
)
O
-
O O
-
O
│ ‖ │ │
[O = C –O
-
↔
-
O –C –O
-
↔
-
O –C = O] ≡ [O –C –O]
2-
v) Nitrate ion (NO
3
-
)
O O
-
O O
↑ | ‖ |
[O = N –O
-
↔ O ← N = O ↔
-
O –N → O] ≡ [O –N –O]
-
Bond Length:
Bond length is defined as the average distance between the centers of nuclei of the
two bonded atoms in a molecule.

24. Partial ionic characters of covalent compounds :
When the covalent bond is formed between two different atoms then the bonding
pair of electron are not lie exactly midway between the two atoms. The electron
attracting tendency of the atoms in a molecule is describe in terms of
electronegativity. More electronegative atom attract the electron pair toward itself,
Which bears the partial negative and partial positive charge on the atoms. As the
difference in electronegativity is increased the covalent bond becomes ionic.
Polar Covalent Bond :
The covalent bond formed between two different atoms having different
electronegativity is called polar covalent bond. The compound formed by such types
of bond are called polar covalent compounds. E.g. HCl, HBr, H
2O etc.

25. Non-polar covalent bond :
The covalent bond formed between two atoms having same electronegativity then
electron pair is equally pulled by both atom as a result polarity is not produced.
Such type of bond is called non-polar covalent bond. The compound formed by
such type of bond are called non-polar covalent compounds. e.g. molecule like
H
2,N
2, Cl
2etc.
Dipole moment :
The ionic character in a covalent molecule is expressed in terms of dipole moment.
It is defined as the product of magnitude of charge on any one of atoms and
distance between them. It is denoted by ‘μ’ and given by
μ= q ×d
Where, q = The magnitude of either charge
d = The distance between positive and negative charge

26. It is a vector quantity and is represented by an arrow pointing from positive centre
to negative centre.
The unit of dipole moment is Debye (D)
1 D = 1 ×10
-18
esu×cm = 1 ×10
-10
A˚
For polyatomic molecule, the total dipole moment is calculated by taking the vector
sum of dipole moment along different atoms with respect to centreatom, which
helps to explain the geometry and polarity of molecule. If the net dipole moment of
polyatomic molecule is zero then the molecule becomes non polar and has regular
geometry and if the net dipole moment of polyatomic molecule is non zero then
molecule becomes polar and has irregular geometry.

27. Application of dipole moment:
1.It determine the ionic character of covalent molecule.
2.It helps to determine the polarity and non-polarity of the molecule.
3.It helps to explain the geometry of some molecules.
CO
2, CS
2, HgX
2etc. ( zero dipole moment value) has linear where as H
2O, H
2S,
SO
2, N
2O, BF
2 etc.(non-zero dipole moment) has bent structure.
Q1. Why water has a bent structure whereas carbon dioxide has linear structure?
Q2. Carbon oxygen bond is polar in CO
2but it is non polar molecule. Why?