Chemical Bonding and Reactions Class 9th Chemistry Notes
Chemical Bonding and Reactions Class 9th chemistry Notes is important chapter in school level chemistry. In this chapter we will study about chemical bonds and chemical reactions, making and breaking bond in chemical reactions, types of chemical bonds like ionic or covalent bond, characteristics of bonds, chemical reactions and type of reactions.
Chemical Bonding
Molecule forms by
the combination of two atoms of elements, the attraction force operate between
atoms is known as Chemical Bonding. Chemical bonds are formed due to presence
of valence electrons in atoms which present in outermost shell of atom.
Question:
Why chemical bonds are formed between atoms?
Answer:
Chemical bonds are formed between atoms to achieve stable state like inert or
noble gases.
Atoms
achieve stable state of nearest inert gas with complete octet in two ways:
1. By
exchanging electron with any other atom.
2. By
sharing electron with any other atom.
Types of Chemical Bonds
1. Electrovalent Bond or Ionic bond
2. Covalent Bond
Electrovalent Bond
Electrovalent
Bond is also known as Ionic Bond because compound formed is ionic in nature
having polarity. In electrovalent bond one atom loose electron to form positive
ion called cation and another which gain electron to form negative ion called
anion. This type of bond is known as Electrovalent Bond or Ionic Bond.
Example: NaCl
Na ---------> Na+ +e-
Cl + e- ---------> Cl-
Na+ + Cl-
---------> NaCl
Electrovalent Compound
The compounds which
contain ionic or electrovalent bonds are known as Electrovalent or Ionic
Compounds. Mainly electrovalent compounds are formed due to reaction between
highly electropositive and highly electronegative atoms.
Characteristics of Electrovalent Compounds
1. Crystal Structure:
In solid state of electrovalent compounds anions
and cations are arranged in regular manner called as crystal, In which anions
surrounded by definite number of cations and cations surrounded by definite
number of anions.
2. Physical Nature:
Ionic or electrovalent
compounds are generally hard and their hardness increases with increasing ionic
charge and decreasing distance between ions.
3. Solubility:
Positive ion of ionic compound attach
with negative part of polar solvent and negative ion of ionic compound attach
with positive part of polar solvent, so ionic or electrovalent compounds are
soluble in polar solvents like water and insoluble in non polar solvents like
benzene, ether, alcohol.
4. Melting Point and Boiling Point:
Electrovalent or ionic compounds have high
Melting and boiling points because they need large amount of energy to break
strong ionic bonds.
5. Electrical Conductivity:
In molten and solution forms electrovalent compounds conduct electricity because ions flow in molten and solution forms.Covalent Compound
Covalent bonds are the bonds which are formed due to
the equal sharing of electrons between two atoms. These chemistry notes are provided by
Chemistry Notes Info Organization www.ChemistryNotesInfo.com , This type of bonds
(i.e. covalent bonds) is formed in atoms which carry four or more than four
electrons in outermost shell, generally sharing of electrons happen in two ways
–
1.
Equal Sharing – Covalent Bond
2.
One Side Sharing – Coordinate Bond
Covalent Compounds
Compound
which are formed as a result of covalent bonding and containing covalent bonds
are known as Covalent Compounds.
Example:
Hydrogen, Chlorine, Oxygen, Water, Ethanol etc.
Types of Covalent Bonds
Covalent
Bonds are of three types which are as follows-
1. Single Covalent Bonds
2. Double Covalent Bonds
3. Triple Covalent Bonds
Single Covalent Bonds
Bonds
which are formed due to sharing of single pair of electrons between two atoms
are called single covalent bond. It is represented by single line (-).
Example:
Formation of H2 molecule, Formation of Cl2 molecule.
i. Formation of Hydrogen (H2) molecule:
In the outermost shell of hydrogen atom, it has single electron, which
it shares with another hydrogen atom to acquire inert configuration of helium so
single bond is formed between these two hydrogen atoms and this single covalent
bond is represented by single line (-).
ii. Formation of Chlorine Molecule (Cl2):
In
the outermost shell of chlorine atom, it has seven electrons, it shares its one
valence electron with another chlorine atom to form chlorine molecule by single
covalent bond.
Double Covalent Bonds
Bonds
which are formed due to sharing of double pair of electrons between two atoms
are called double covalent bond. It is represented by double line (=)
Example:
Formation of O2 molecule.
i. Formation of Oxygen (O2) molecule:
In the outermost shell of oxygen atom, it
has six electrons, it shares its two valence electrons with another oxygen atom
to form oxygen molecule by double covalent bond.
Triple Covalent Bonds
Bonds
which are formed due to sharing of triple pair of electrons between two atoms
are called triple covalent bond. It is represented by triple lines
Example:
Formation of N2 molecule.
i. Formation of Nitrogen (N2) molecule:
In the outermost shell of nitrogen atom, it
have five electrons, it share its three valence electrons with another nitrogen
atom to form nitrogen molecule by triple covalent bond.
Characteristics of covalent compounds
1. Crystal Structure:
Crystal structure of covalent compounds is
formed from atoms or molecules. Crystal of covalent compounds are divided in
three parts as –
i.
These are crystals of covalent compounds
whose molecule are very small and these molecules are held together by vander
waals forces.
Example:
Sulphur, Iodine.
ii.
These are crystals of covalent compounds
whose molecule are very large due to combination of every atom with other atom
by covalent bonds.
Example: Diamond, Silica.
iii.
These are crystals of covalent compounds
whose have separate layers.
Example: Graphite.
2. Physical Nature:
Due to weaker force of attraction
between the molecules of the covalent compounds, maximum covalent compounds are
gases or liquids but some covalent compounds exist as solid like Urea, Sugar,
Glucose, and Naphthalene.
3. Solubility:
Covalent compounds are not soluble in polar solvents like water but are soluble in non-polar solvent like alcohol, ether, carbon tetra chloride.4. Melting Point and Boiling Point ( MP and BP) :
Melting and boiling
points of covalent compounds are very low because very less energy is required
to overcome the weak force of attraction between the neutral molecules in the
covalent compound. But Diamond and Graphite are exception because they have
very high melting and boiling points.
5. Conductivity:
Covalent compounds do not have ions so they do not conduct electricity but some polar covalent compounds conduct very less electricity.Polar Covalent Bond
In the
covalent compound if one is the more is more electronegative than other atom,
then shared pair of electrons is attracted towards more electronegative atom so
it acquire or obtain some partial negative charge which is represented by delta
negative (d-)
and other atom acquire some partial positive charge which is represented by
delta positive (d+) therefore polar bond is form, which
is known as Polar covalent bond.
Example : Hydrogen Chloride Molecule.
In HCl molecule, Chlorine is more
electronegative than Hydrogen so chlorine acquires partial negative charge and
hydrogen acquire partial positive charge.
Characteristics of Polar Covalent Compounds
i.
Polar
covalent compounds are approximately 80% covalent and 20% ionic so they so characteristics
of both covalent and ionic (or electrovalent) compounds.
ii.
In
solution forms, polar covalent compounds are good conductor of electricity.
Example: HCl
iii.
As
compared to pure non-polar covalent compounds and electrovalent compounds, the
melting point and boiling point of polar covalent compound are higher.
Chemical Reactions
Chemical Reaction is the reaction
in which two or more than two substances react to form a new substance is known
as Chemical Reaction. The substances which react may be ion or compound
of element.
Reaction:
Reactant reacts with each other to give product.
Reactant ---------> Product
Example of general chemical reactions
from daily life is rusting of iron, formation of curd from milk etc.
Chemical Formula
Chemical Formula
is simple representation of any compound by writing together the numbers and
symbols of constituting elements forming that compound.
Example: H2O, CaCl2,
AlCl3, Ca(OH)2
Chemical Formula for Ionic Compounds
As
we know Ionic compound formed as a result of electron transfer between metal
and non-metal atoms. When we have to write chemical formula for ionic compound
then write metal atom symbol on left hand side and non-metal atom symbol on
right hand side. Metal atom name remain same but ‘ide’ or ‘ate’ suffix is added
to non-metal atom name.
Ionic compound formed by one metal atom and non-metal atoms.
Metal Atom
|
Non-Metal Atom
|
Name of Compound
|
Chemical Formula of Compound
|
||
Name and Symbol
|
No.
|
Name and Symbol
|
No.
|
||
Calcium (Ca)
|
1
|
Oxygen (O)
|
1
|
Calcium Oxide
|
CaO
|
Magnesium (Mg)
|
1
|
Chlorine (Cl)
|
2
|
Magnesium Chloride
|
MgCl2
|
Aluminium (Al)
|
1
|
Chlorine (Cl)
|
3
|
Aluminium Chloride
|
AlCl3
|
Chemical Formula for Covalent Compounds
As
we know covalent compound formed as a result of electron sharing and contains
non-metal atoms. When we have to write chemical formula for covalent compound
then relatively less electronegative non-metal atom symbol is written on left
hand side and other witch is more electronegative is written on right hand side. Name of non-metal atom
which is written on left hand side is remain same but ‘ide’ suffix is added to
non-metal atom name which is written on right hand side.
Covalent compound formed by two non-metal atoms.
Low Electronegative
Non-Metal Atom
|
High Electronegative
Non-Metal Atom
|
Chemical Name of
Compound
|
Chemical Formula of Compound
|
||
Name and Symbol
|
No.
|
Name and Symbol
|
No.
|
||
Carbon (C)
|
1
|
Oxygen (O)
|
1
|
Carbon Mono Oxide
|
CO
|
Carbon (C)
|
1
|
Oxygen (O)
|
2
|
Carbon Di Oxide
|
CO2
|
Phosphorus (P)
|
1
|
Chlorine (Cl)
|
3
|
Phosphorus Tri Chloride
|
PCl3
|
Phosphorus
(P)
|
1
|
Chlorine (Cl)
|
5
|
Phosphorus Penta Chloride
|
PCl5
|
Nitrogen
(N)
|
2
|
Oxygen (O)
|
5
|
Nitrogen Penta Oxide
|
N2O5
|
Formation of Compound
We
get chemical formula of molecule by writing valence of 1st atom in
front of 2nd atom and valence of 2nd atom in front of 1st
atom.
Example: valence of carbon is 4 and oxygen is 2, write
4 in front of O and 2 in front of C in subscripts as shown below.
C2O4
as we see, both valences are multiple of two so
divide it by two to get CO2 formula.
Similarly,
Na+
+ CO3-2 ----> Na2CO3
Al+3
+ SO4-2 ---->
Al2(SO4)3
Mg+2
+ N-3 ----> Mg3N2
Simple Chemical Reaction
Chemical reaction is represented by chemical
equation in brief by taking help of symbol and formula of participating
substances in reaction.
General Rule for writing Simple Chemical Reaction
1. Reactant
are written on left hand side and if more than one reactant are present than
write plus (+) sign between them.
2. Product
are written on left hand side and if more than one product are present than
write plus (+) sign between them.
3. Arrow
sign is placed between reactants and products.
Example: Zn + H2SO4
( Reactants) ----->
ZnSO4 + H2 (Products)
4. To
get more information from the reaction write temperature, pressure, catalyst
name above or below arrow sign.
sign and on
the left side of heavy substances which precipitate 
sign is placed.
6. Reactions
which absorb heat are known as endothermic reactions and (+Q)
heat sign is added on reactant side.
7. Reactions
which produce heat are known as exothermic reactions and (+Q)
heat sign is added on product side.
8. (Aq)
is written for aqueous solution substances.
Balancing of Chemical Reactions
For balancing of chemical reaction, the no.
of atom on reactant side should be equal to no. of atom on product side, so
that total mass of reactant is equal to total mass of product. You read these 9
class notes at www.ChemistryNotesInfo.com
of ‘Chemistry Notes Info’ organization website.
H2 + O2 ----->
H2O (Imbalance Equation)
2H2 + O2 ----->
2H2O (Balance Equation)
Types of Chemical Reaction
· Addition Reaction
· Decomposition Reaction
· Substitution Reaction
· Oxidation and Reduction Reaction
1. Addition Reaction
Reactions in which two or more than two substances
reacts together to produce a new compound is known as Addition Reaction.
Example:-
2Mg
+ O2 ------>
2MgO
2. Decomposition Reaction
Reactions in which one compound get break into two
or more than two simple compounds by breaking of chemical bonds, these chemical
bonds get broken by heat, light or electricity.
Example:-
CaCO3
------> CaO + CO2
3. Substitution Reaction
Reactions in which one element replaces another
element to form a new compound is known as Substitution Reaction
Example:-
CuSO4
(Aq) + Zn (s) ------> ZnSO4 (Aq) + Cu (s)
4. Oxidation and Reduction Reaction
Oxidation and reduction reaction are described below
on these two bases-
Oxidation and Reduction Reaction
based on oxygen and hydrogen-
· Removal of hydrogen and addition of
oxygen is known as oxidation reaction.
· Removal of oxygen and addition of hydrogen
is known as reduction reaction.
Oxidation and Reduction Reaction
based on electron transfer-
·
Oxidation reactions are the reactions in
which atom or ion loses electrons.
· Reduction reactions are the reactions in
which atom or ion gains electrons.
Oxidation
and Reduction reactions occurs simultaneously because electron removed from one
atom or radical is added to another atom or radical.
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