1. Lecture- 2
Sn2+
Fe2+
---------------> Sn4+ + 2e–
---------------> Fe3+ + e–
Electronic Concept of oxidation and reduction
Oxidation is a process which involves loss of electrons by an atom or
group of atoms.
For example,
(i) Loss of electrons resulting in increase in positive charge.
Na ---------------> Na+ + e–
Mg ---------------> Mg2+ + 2e–
2. Lecture- 2
MnO42–
[Fe(CN)6]4–
--------------->
--------------->
MnO4 + e
– –
[Fe(CN)6]3– + e–
Electronic Concept of oxidation and reduction
Oxidation is a process which involves loss of electrons by an atom or
group of atoms.
For example,
(ii) Loss of electrons resulting in decrease of negative charge.
3. Lecture- 2
Fe3+ + e– ---------------> Fe2+
Sn4+ + 2e– ---------------> Sn2+
Sb5+ + 2e– ---------------> Sb3+
Electronic Concept
Reduction : A process which involves gain of electrons by an atom or group
of atoms.
(i) Gain of electrons resulting in decrease of positive charge.
4. Lecture- 2
S + 2e– ---------------> S2-
Electronic Concept
Reduction : A process which involves gain of electrons by an atom or group
of atoms.
(ii) Gain of electrons resulting in increase of negative charge.
Cl2 + 2e– ---------------> 2Cl–
5. Lecture- 2
Lets Understand !!
OXIDATION-REDUCTION REACTIONS AS ELECTRONS TRANSFER
REACTIONS
Oxidation takes place at the cost of reduction and vice versa.
7. Lecture- 2
Lets Understand !!
OXIDATION NUMBER
The charge which an atom of the element has in its ion or appears to have
when present in the combined state with other atoms.
Oxidation numbers are also called oxidation states.
Oxidation number also gives the charge which an atom appears to have
when all other atoms are removed from it as ions.
8. Lecture- 2
Rules for the Determination of Oxidation Number of an Atom
1. The oxidation number of an element in the free or elementary state or in
any of its allotropic forms is always zero.
9. Lecture- 2
Rules for the Determination of Oxidation Number of an Atom
2. The oxidation number of an element in a single (monoatomic) ion is the
same as the charge on the ion.
10. Lecture- 2
Rules for the Determination of Oxidation Number of an Atom
3. In compounds formed by the combination of non-metallic atoms, the atom
with higher electronegativity is given negative oxidation number.
11. Lecture- 2
Rules for the Determination of Oxidation Number of an Atom
4. In all compounds of hydrogen, the oxidation number of hydrogen is +1
except in hydrides of active metals such as LiH, NaH, KH, MgH2, CaH2,
etc., where hydrogen has the oxidation number of –1.
12. Lecture- 2
The second exception is found in compounds in which oxygen is bonded to
fluorine.
Rules for the Determination of Oxidation Number of an Atom
5. The oxidation number of oxygen is –2 in most of the compounds.
However, there are two exceptions. The first exception is peroxides and
superoxides
13. Lecture- 2
Rules for the Determination of Oxidation Number of an Atom
6. The most electronegative element, fluorine has oxidation number –1. For
other halogens, the oxidation number is generally – 1, but there are
exceptions when these are bonded to a more electronegative halogen atom
or oxygen.
14. Lecture- 2
For a polyatomic ion, the sum of the oxidation numbers of all the atoms is
equal to charge on the ion.
Rules for the Determination of Oxidation Number of an Atom
7. For neutral molecule, the sum of the oxidation numbers of all the atoms is
equal to zero.
15. Lecture- 2
Oxidation Number of
1. Free elements
2. Fluorine
3.a) Simple ions
b)Oxygen
= 0
= –1
= Charge on them
= OXIDES (–2);
peroxides (–1);
F2O (+ 2); F2O2 (+ 1)
b)metal hydrides
4. a)Hydrogen = + 1;
(–1)
5. Sum of O.N. of atoms in molecules = 0
6. Sum of O.N. of atoms in polyatomic ions = (Charge on them).
Watch out !!
16. Lecture- 2
Can you Crack it !!
1. Calculate the oxidation number of sulphur in the following molecules & ions :
(a) H2S
17. Lecture- 2
Can you Crack it !!
1. Calculate the oxidation number of sulphur in the following molecules & ions :
(b) H2SO3
18. Lecture- 2
(c)
Can you Crack it !!
1. Calculate the oxidation number of sulphur in the following molecules & ions :
SO2–
4
19. Lecture- 2
Can you Crack it !!
Calculate the oxidation number of sulphur in the following molecules & ions :
(d) Na2S2O3
20. Lecture- 2
(e) S2O2–
7
Can you Crack it !!
Calculate the oxidation number of sulphur in the following molecules & ions :
21. Lecture- 2
Can you Crack it !!
Calculate the oxidation number of sulphur in the following molecules & ions
(f) H2
SO4
22. Lecture- 2
(g) S2O2–
4
Can you Crack it !!
Calculate the oxidation number of sulphur in the following molecules & ions
23. Lecture- 2
Can you Crack it !!
2. What is the oxidation number of the underlined atoms in each of the
following molecules OR ions ?
(a) ClO– (b) BrF
3 3
24. Lecture- 2
(c) CH4 (d) C6H12O6
Can you Crack it !!
2. What is the oxidation number of the underlined atoms in each of the
following molecules OR ions ?
25. Lecture- 2
Can you Crack it !!
2. What is the oxidation number of the underlined atoms in each of the
following molecules OR ions ?
(e) Na2B4O7 (f) Na4[Fe(CN)6]
26. Lecture- 2
Can you Crack it !!
2. What is the oxidation number of the underlined atoms in each of the
following molecules OR ions ?
(g) N2H4
27. Lecture- 2
number of underlined elements in the
CO2
Cr2O7
2–
Can you Crack it !!
3. Calculate the oxidation
following species:
28. Lecture- 2
3. Calculate the oxidation number of underlined elements in the
Can you Crack it !!
CH2Cl2
following species:
Pb3O4
29. Lecture- 2
number of underlined elements in the following
3,
Can you Crack it !!
3. Calculate the oxidation
species:
PO3– ,
4
30. Lecture- 2
number of underlined elements in the following
3. Calculate the oxidation
species
HNO3, K2MnO4,
NH+
4
Can you Crack it !!
31. Lecture- 2
Finally u must know !!
Oxidation: Process involving loss of one or more electrons
Reduction: Process involving gain of one or more electrons
Oxidizing agents: Species which gain one or more electrons
Reducing agents: Species which lose one or more electrons
36. Lecture- 2
number of underlined elements in the following
3. Calculate the oxidation
species:
CO2 , Cr2O4, Pb3O4, CH2Cl2, PO3– , S O2– , HNO , K MnO , NH+
4 2 3 3 2 4 4
Can you Crack it !!
![Lecture- 2
MnO42–
[Fe(CN)6]4–
--------------->
--------------->
MnO4 + e
– –
[Fe(CN)6]3– + e–
Electronic Concept of oxidation and reduction
Oxidation is a process which involves loss of electrons by an atom or
group of atoms.
For example,
(ii) Loss of electrons resulting in decrease of negative charge.](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)