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Friday, 15 May 2015

Class 9 Chemical Bonding and Reactions CHEMISTRY LECTURE NOTES part 1


Chemical Bonding and 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 octate 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 flows in molten and solution forms.

9th Class Chemical Bonding and Reactions Part 2
9th Class Chemical Bonding and Reactions Part 3 

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