Chemical Bonding and Molecular Structure Class 11
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