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21 Chemistry -- Oxidation and Reduction

Differences between O.N. and Valency

Differences between O.N. and Valency

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O.N.Valency
It is the charge appeared on the atom.
eg: O.N. of C in HCHO is 0.		It is the no. of electrons lost, gained or shared by an atom of an element.
eg: Valency of C in HCHO is 4.
It may be zero, positive, negative or even in fraction.
eg: O.N. of N in (hydrozoic acid) N3H is -1/3 and in NH3 is -3.		It is a whole number with positive or negative sign.
eg: Valency of N in N3H and NH3 is 3.
It may be different for the same element in the different compounds.
eg: O.N. of C in CH4, CH3Cl, CH2Cl2, CHCl3 and CCl4 are -4, -2, 0, +2 and +4 resp.

Except variable valency, elements have constant valency.
eg: Valency of C in CH4, CH3Cl, CH2Cl2, CHCl3 and CCl4 is 4.



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Notes of oxidation and reduction. anyone please.?!?

In terms ofClassical idea:

Oxidation: Addition of oxygen or any other electronegative element to a substance .Conversely , Removal of Hydrogen or any other electropositive element from a substance.

Mg (s) + S (s) MgS (s)

Similarly,Reductionis just opposite process of oxidation.

2FeCl3(aq) + H2(g)2FeCl2(aq) + 2HCl (aq)

In terms ofElectron transfer reaction:
Oxidation: Loss of electron
Reduction: Gain of electron
Oxidant: Acceptor of electron
Reductant: Donor of electron

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  • Reduction: The addition of hydrogen or electropositive radical/element or removal or oxygen or electronegative element/radical is said to be reduction.
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Calculate the oxidation number of the underlined elements:

Let the oxidation number of each element to be found be x in each cases.

Here,ON of K, H = 1;ON of O = -2

a) KMnO4

It is a molecule hence, the ON of the molecule is zero.

1 + x + 4(-2) = 0

1 + x - 8 = 0

x - 7 = 0

x = 7

b) K2Cr2O7

It is a molecule hence, the ON of the molecule is zero.

2(1) + 2(x) + 7(-2) = 0

1 + x - 7 = 0

x - 6 = 0

x = 6

c) H2SO4

It is a molecule hence, the ON of the molecule is zero.

2(1) + x + 4(-2) = 0

2 + x - 8 = 0

x - 6 = 0

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Oxidation State Valency
Total number of electrons and atom can share lose or gain in order to form a bond with another atom. Total number of electrons present in the valence shell of any atom.
Represents the electrical charge of any electron in an atom.

Does not represent the electrical charge of any electron in an atom.
For any pure element, oxidation number is always zero For any pure element, its valency depends upon the total number of electrons present it's valence shell.
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