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Chemistry Podcast

Saturday, 26 April 2014

11 Class Chapter 4- Chemical Bonding and Molecular Structure

Chemical Bonding and Molecular Structure

Attractive force which held’s various constituents (like atoms, ions etc.) together in difference chemical species is known as a chemical bond.

Kossel Lewis Approach to Chemical Bonding: -

                                                                        Lewis discussed that atoms achieve stable octet when they linked by chemical bonds.
·        In  NaCl, an electron transfer from  Na to Cl and give Na+ and Cl-  ions and ,
·        In case of Cl2,H2,F2,  sharing of electron takes place to complete stable outer octet.
·        Valence electrons take part in chemical reaction or combination.
·        Symbol to represent valence electron in atom is known as Lewis symbol.

·        Significance of Lewis symbol :- 

To calculate valence = (no. Of dots and or / eight minus no. Of dots)

Octet rules  :- 

                    According to this rule , atoms can combine either by sharing electron or by transfer (gaining or losing ) of electron to complete octet (i.e. 8 electron in outer most shell).

Covalence bond  :-   

                          Bond forms by sharing of electrons.
·        When sharing of one pair of electron takes place is known as single covalent bond.
·        When sharing of two pair of electrons takes place is known as double bond.
·        When sharing of three pair of electron takes place is known as triple bond.

Formal charge (F.C.)  : - 

For polyatomic molecule or ion, formal charge of an atom in a Lewis structure = [Total no. of                 Valence electron in free Atom] - [total no. of non bonding (lone- pair) elements]- 1/2[total no of bonding (shared) electrons]
Ex  :-  Lewis structure of O3 (ozone molecule)
Atoms in O3 is marked as 1,2,3
·        Central  O  atom marked as 1
·        Central  O  atom marked as 2
·        End O atom marked as 3

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