Oxygen – Types of oxides and Uses of hydrogen peroxide.

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structure of oxygen molecule

Symbol : O

Molecular formula : O2

Atomic number : 8

Atomic weight : 15.999 amu

Molecular weight : 32

Electronic configuration: 1s22s22p4

Isotopes : 8O16, 8O17, 8O18

Discovered by : Joseph Priestly

→ Most abundant element in earth crust, about 41%.

→ Discovered by English scientist, Joseph Priestley who obtained oxygen by focusing the sun-rays with the help of a lens on mercuric oxide.

→Lavoisier investigated its properties in detail.

→ Exist in diatomic gaseous molecule (O2)

Position of oxygen in the periodic table

The electronic configuration of oxygen is 1s22s22p4. So this element is placed in the p-block in the group VIA or group 16 along with sulphur(S), selenium(Se), Tellurium(Te) and Polonium(Po).Polonium is radioactive and metalloid, while others are non-metals.

Gr VIA elements together are called chalcogens (ore forming) because their metallic compounds occur in nature in the form of oxides, sulphides, selenides and tellurides as ores. Only oxygen exists in gaseous state in its group.

 position of oxygen in periodic table

Uses of oxygen

  1. It is used for artificial respiration in hospital.
  2. It is used in rocket fuel. { A mixture of fuel and liq. Oxygen is used to obtain a high speed in high altitude rockets, jets and missiles.}
  3. It is used for the preparation of compounds like H2SO4, HNO3, CO2, etc.
  4. It is used as an oxidizing agent in chemical reactions.

Allotropes of oxygen

Allotropes are two or more forms of the same element in the same physical state (solid, liquid, or gas) that differ from each other in their physical, and sometimes chemical properties.

There are two main allotropes of oxygen:

  1. A diatomic molecule made up of 2 oxygen atoms with the moelcular formula O2 commonly referred to as molecular oxygen or dioxygen.
  2. A triatomic molecule made up of 3 atoms of oxygen with the molecular formula O3 referred to as ozone.

Note : Other allotropes are O4, O8, etc.

Oxides

Oxides are binary compounds of oxygen with other elements which are less electronegative than oxygen . eg. CO2, CO, Fe2O3, CaO, Na2O, H2O, etc.

Note : Binary compounds means compounds having only two types of elements. Binary compounds of oxygen like OF2, O2F2, etc are not oxides, they are fluorides.

Classification of oxides

A. On the basis of acidic and basic behavior :
1. Basic oxides :

Oxides of metals which dissolve in water to form base( alkali) and react with acids to form salt and water are called basic oxides. Eg. Na2O, H2O, MgO, CaO, BaO, Li2O, {CuO, MnO, FeO} etc.

Generally, oxides of group IA metals are basic. {except BeO which is amphoteric.}Eg.

basic oxides

Oxides of d-block elements in the lower oxidation states are basic. They are not soluble in water but react with acid to form salt and water. Eg.

2. Acidic Oxides :

Oxides of non-metals which dissolve in water to form acids and react with bases to form salt and water are called acidic oxides. Eg. SO2, CO2, SO3, NO2, N2O3, N2O5, etc.

acidic oxides

3. Neutral oxides :

Oxides which neither react with acids nor with bases are called neutral oxides. Eg H2O, CO, NO, N2O, etc.

4. Amphoteric oxides :

Oxides which react with acids as well as with base to form salt and water are called amphoteric oxides. Eg. ZnO, SnO, PbO, Al2O3, {BeO,} etc.

amphoteric oxides

Trend in the periodic table :

On moving from left to right in a period, metallic character decreases and basic character decreases.

Period 3 Na Mg Al Si P S Cl
Oxide Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl2O7
Acidic/basic behaviour Strongly basic basic amphoteric Weakly acidic acidic Strongly acidic Very strongly acidic

On moving from top to bottom in a group, metallic character increases and basic character increases. Eg. Oxides of group 13 elements:

Group 13 oxides behavior
B B2O3 Weakl acidic
Al Al2O3 Amphoteric
Ga Ga2O3 Amphoteric
In In2O3 Basic
Tl Tl2O3 More basic

In oxides of the same element, acidic character increases with increase in oxidation number or number of oxygen atoms. Eg.

Oxides of nitrogen N2O NO N2O3 NO2 N2O5
O.N. of nitrogen +1 +2 +3 +4 +5
Acidic character neutral neutral acidic acidic acidic

Acidic order : N2O < NO < N2O3 < NO2 < N2O5

B. On the basis of structural considerations:
1. Normal oxides :

Oxides formed by normal valency rule are called normal oxides. Eg. Na2O, MgO, ZnO, Al2O3, etc. where valency of O = 2 .

2. Peroxides :

Oxides which contain peroxide ion O22- or (O-O)2- in which the oxidation number of oxygen is -1 and produce hydrogen peroxide with acid are called peroxides. Eg. H2O2 { i.e. H-O-O-H} , Na2O2, K2O2, BaO2, etc.

BaO2 : {i.e. Ba-O-O}

peroxides

Alkali metals form peroxides of type M2O2 and alkaline earth metals form peroxide of type MO2.

Note : PbO2(lead peroxide) and MnO2 are not true peroxide as they do not produce H2O2 with dil. acid.
3. Super Oxides :

Oxides which contain superoxide ion O2– in which the oxidation number of oxygen is -1/2 are called superoxides. Eg. KO2{potassium superoxide}, RbO2, CsO2, etc.

i.e. oxides containing more oxygen atoms than required by the normal valency rule are called superoxides.

4. Suboxides :

Oxides which contain less oxygen atoms than required by the normal valency rule are called suboxides. Eg. N2O(nitrogen suboxide}, Pb2O, C3O2, etc.

5. Mixed oxides :

Those oxides which are a mixture of two similar oxides of the same element in different valency are called mixed oxides. Eg.

mixed oxides

Uses of hydrogen peroxide

  1. It is used as an antiseptic for washing wounds, animal bites, etc.
  2. It may also be used as a mouth rinse to help remove mucus or to relieve minor mouth irritation.
  3. It is used as bleaching agent for hair, wool, silk, etc.
  4. It is used to remove stains.
  5. It is used as good oxidizing agent in the laboratory.

hydrogen peroxide uses

Questions and answers

1.Which of the following is not a oxide ?

a. CO2     c. H2O

b. OF2     d. BaO2

2. Which of the following is amphoteric oxide?

a. PbO      c. O2

b. N2O3    d. K2O

3. Which of the following is peroxide?

a. Na2O      c. MgO

b. Al2O3      d. BaO2

4. Which of the following is most acidic oxide?

a. Na2O      c. P2O5

b. Al2O3      d. SO3

5. Which of the following is most basic oxide ?

a. Al2O3       c. In2O3

b. Ga2O3      d. Tl2O3

6. Which of the following is most acidic oxide?

a. N2O      c. NO2

b. NO       d. N2O3

Answer :

1.- b ; 2.- a ; 3.- d ; 4.- d ; 5.- d ; 6. – c

References