Class 9 Chemical Bonding and Reactions SCIENCE LECTURE NOTES part 3 | Chemistry Notes Info - Your Chemistry Tutor provide notes for Classes, BSc, MSc, Chemistry Test

Class 9 Chemical Bonding and Reactions SCIENCE LECTURE NOTES part 3

Chemical Bonding And Reactions

   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. 
   5.     On the right side of the gaseous substances 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 basis-
          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 looses 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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