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Limitations of the concept of oxidation number

Prepare for the upcoming XI exam by learning the basic concept of oxidation and oxidation numbers or oxidation state with the help of the periodic table.

Introduction

Oxidation is a vital chapter in chemistry for the students who are aiming to crack the class XI final with good marks. Oxidation states of oxidation number is a very basic and very interesting subject for students who like chemistry. The periodic table is a very vital aspect of this chapter and it contains many important questions for the upcoming class XI examination.

Unacademy is here to present the concept of oxidation, oxidation number, and many more brief discussions in this chapter with illustrative examples.  Unacademy has vastly detailed discussions available on the periodic table. This paper contains 1st twenty-five descriptions of periodic table elements and their oxidation number.

Concept of oxidation

Oxidation is a process that involves the addition of oxygen or the deduction of hydrogen from any electropositive or electronegative element.  According to the electronic concept, oxidation is a process in which an ion or atom loses one or more than its electrons. 

In simple words, oxidation is a process in which due to the addition of oxygen the substance of a chemical is used to change its structure. As an example, in the reaction between oxygen and magnesium metal, oxygen involves the oxidation of magnesium. When oxygen and silicon get exposed, the silicon undergoes oxygen and forms silicon oxide.

Concept of oxidation number

The oxidation number is also known as oxidation state, is the state of an atom, in a chemical compound that provides insight into the number of oxygen electrons reduced. It also describes the extent of oxidation of the atom. The oxidation states can also be defined as the hypothetical charge that can be held by that atom if all its bonds with the other atoms were ionic.

For example, if we take CO2, then the oxidation state of carbon would be +4. In the hypothetical charge, held by the carbon atom will be doubled if the oxygen-carbon bond was completely ionic and equal to +4.  Simply, it can be defined that the oxidation number or state is used interchangeably to describe the quantities of electrons lost in the atom.  The oxidation state can be negative, positive, or zero.

Types of oxidation number and examples

There are two states of oxidation of any element. One is the lowest oxidation state and the other is the higher state. In any chemical reaction, if there is an increase in the oxidation number then it is known as oxidation. On the other hand, if there is a decrease in the state then it is known as reduction.  The lowest state is -4, which is for carbon in methane or CH4. The highest state is +9 in Iridium tetroxide or IX.

Calculation of oxidation number

There are six certain rules to calculate the oxidation number.

  •   In an element, each atom is either uncombined or freeholds up an oxidation number of zero. Such as CL2, H2, Na, O3, O2, S8, P4, AI, and Mg, which have zero number oxidation.
  •   The state of ions which only comprises one atom is equal to the actual charge of the ion.
  •   In most of the compounds, the oxidation number is – 2
  •   Oxidation of hydrogen is +1, except when it is bonded with metals that also contain two elements. For example, CaH2 where the oxidation number is -1.
  •   Halogens and fluorine have the number of oxidation -1, especially when they appear as halide ions in the compounds. Again there is an exception. When chlorine, bromine, and iodine are combined with Oxygen, the number becomes positive.
  •   When the number of oxidation of an atom of a compound is added, the algebraic sum of that must be equal to zero.

Example of oxidation number calculation

  • The oxidation number of nitrogen (N) in NO

The atomic number of Nitrogen is 7. The calculation of the electronic configuration is,

N (Z=7) = 1s2 2s2 sp3

If the oxidation number of N= x,

Therefore, X + (-2) = 0

X = +2

So, the oxidation number of nitrogen is +2.

The oxidation number of S in H2SO5

Oxidation No of OH= -1

Oxidation No of Oxygen= -2

Therefore he states of Sulfur or H2SO5 = x – 2 – 2 -1 – 1 = 0 ⇒ x = +6

The oxidation number of P in H3PO4

The oxidation number of hydrogen= +1

Oxygen = -2

Therefore, P = 3(+1) +x + 4(-2) = 0 ⇒ x = +5

Oxidation number list of first 25 elements from the periodic table

Element

Oxidation Numbers

  1. Hydrogen (H)

+1,0,-1

  1. Helium (He)

No oxidation

  1. Lithium (Li)

-1

  1. Beryllium (Be)

+1,+2

  1. Boron (B)

+1,+2,+3,0,-1,-3

  1. Carbon (C)

+1,+2,+3,+4,0,-1,-2,-3,-4

  1. Nitrogen (N)

+1,+2,+3,+4,+5,0,-1,-2,-3

  1. Oxygen (O)

+1,+2,0,-1,-2

  1. Fluorine (F)

-1

  1. Neon (Ne)

0

  1. Sodium (Na)

+1,-1

  1. Magnesium (Mg)

+1,+2

  1. Gold (Au)

-1,-2,+1,+2,+3

  1. Silicon (Si)

+1, +2, +3,+4,-1,-2,-3,-4

  1. Phosphorus (P)

+1,+2,+3,+4,+5,0,-1,-2,-3

  1. Sulfur (S)

+1,+2,+3,+4,+5,+6,0,-1,-2

  1. Chlorine (Cl)

+1,+2,+3,+4,+5,+6,+7,0,-1

  1. Argon

0

  1. Potassium (K)

+1,-1

  1. Calcium (Ca)

+1,+2

  1. Scandium (Sc)

+1,+2,+3

  1. Titanium (Ti)

+1,+2,+3,+4,-1,-2

  1. Vanadium (V)

+1,+2,+3,+4,+5,-1,-3

  1. Chromium (Cr)

+1,+2,+3,+4,+5,+6,-1,-2,-4

  1. Manganese (Mn)

+1,+2,+3,+4,+5,+6,+7,-1,-2,-3

Conclusion

There are 118 total elements in the periodic table, and each one of them has a different oxidation number. Along with that, there are more related important questions available from this chapter, which is important for class XI, exam preparation. It is high time to prepare for your upcoming examinations. The oxidation and related terms are common and known by all students from classes 11 and 12. However, this chapter is vital for your preparation for class XI finals. For the last few years, there have been many scoring questions coming from this chemistry chapter. This chapter is very interesting and easy to understand, once the concept is clear.