Oxygen

Symbol: O
Atomic number: 8
Molecular formula: O₂
Atomic mass: 16 amu
Electronic configuration: 1s² 2s² 2p⁴
Electronegativity: 3.5

Position of oxygen in periodic table:

Oxygen is kept in group VIA or group 16 in the periodic table along with sulphur, selenium, tellurium, and polonium. Oxygen and sulphur are non-metals, selenium and tellurium are metalloids and polonium is metallic in nature. The Oxygen family is also called chalcogens (ore-forming) because they exist in nature as ore.

Allotropy:

Allotropy is the property of an element existing in two or more different forms in the same physical state. The different forms of the same elements are called allotropes and the phenomenon is called allotropism.
Allotropes of oxygen are O₂(dioxygen) and O₃(trioxygen).

Oxides:

Oxides are binary compounds of oxygen with other elements which are less electronegative than oxygen.

Types of oxides:

1. Acidic oxide: Acidic oxides are non-metallic oxides that combine with water to produce an acid and react with base to produce salt and water.
   eg. SO₂, SO₃, CO₂, NO₂, P₂O₅, etc.

2. Basic oxides: Basic oxides are metallic oxides that combine with water to produce base and react with acid to produce salt and water.
   eg. Na₂O, K₂O, CaO, MgO, Cu₂O, FeO, BaO, etc.

3. Neutral oxides: Oxides which neither react with acids nor with base are called neutral oxides.
   eg. H₂O, N₂O, CO, NO, etc.

4. Amphoteric oxides: Oxides that react with both acids as well as bases to form salt and water are called amphoteric oxides.
   eg. ZnO, Al₂O₃, PbO, SnO, BeO, As₂O₃, etc.

5. Peroxide: Oxides that contain peroxy linkage (-O-O-) and oxygen has a -1 oxidation number are called peroxides.
   eg. H₂O₂, Na₂O₂, BaO₂, etc.

6. Mixed or compound oxides: Oxides that are a mixture of two simpler oxides of the same element in different valency are called mixed oxide. eg. Pb₃O₄ (PbO + PbO₂), Fe₃O₄ (FeO + Fe₂O₃ , Mn₃O₄ (MnO + MnO₂).

Applications of Hydrogen peroxide

• It is used as an oxidizing agent.
• It is used as a bleaching agent.
• It is used as an antiseptic.
• It is used to prepare many organic peroxides.
• It is used in the preparation of toothpaste.

Medical application of oxygen:

• All living cells need a constant supply of oxygen for aerobic respiration.
• Oxygen treatment is required to avoid hypoxemia and tissue hypoxia.
• Medical oxygen is used in the treatment of pneumonia, heart attack, and pulmonary disease.
• A medical supply of oxygen is required to treat respiratory distress syndrome in newborns.
• Oxygen therapy is essential for poisoning, cardiac or respiratory arrest, shock, and serious trauma patients.

Industrial application of oxygen

• Oxygen is necessary for the combustion of fuel required to run the machine, furnace, etc.
• Oxygen is required to make the oxy-acetylene flame to make high temperatures for cutting and welding metals.
• It is used in glass and ceramic manufacture.

Ozone

There is a layer of ozone in the atmosphere from 12- 24 km from the surface of the earth. Ozone is formed naturally in the stratosphere by the action of ultraviolet radiation from the sun on oxygen.

Preparation of ozone from oxygen

Ozone is prepared by passing a silent electric discharge through pure and dry oxygen at low temperatures in an apparatus called ozonizer.

Structure of ozone:

It has an angular structure with a bond angle of 116°. Both the bond lengths are equal (1.29 °A) which is intermediate between O-O single bond length (1.48 °A) and O-O double bond length (1.10 °A). This indicates ozone molecule is a resonance hybrid of the resonating structures.

Test of ozone:

1. It is pale blue gas with a pungent odour.
2. Tailing of mercury
   
   2Hg + O₃ → Hg₂O + O₂
   
   When mercury is exposed to the atmosphere of ozone, it is oxidized into mercurous oxide. Mercury loses its meniscus and sticks on the glass surface leaving a tail. This is called the tailing of mercury.

3. It turns starch iodine paper into blue.
   
   2KI + H₂O + O₃ → 2KOH + O₂ + I₂
   I₂ + Starch → blue color

Depletion of ozone layer:

The ozone layer absorbs ultraviolet radiation from the sun and protects the living beings on the earth from the harmful effects of ultraviolet radiation. However, the ozone layer is depleting mainly due to man-made chlorofluorocarbons (CFCs), also known as freons which are compounds of carbon, fluorine, and chlorine.

CF₂Cl₂ CF₂Cl + Cl
Cl + O₃ → O₂ + OCl
OCl O + Cl
O + O₃ → 2O₂

Harmful effects of ozone layer depletion:

• Causes skin burn, skin cancer, damage DNA
• Reduction in crop fertility
• Change in global warming and climate

Control of ozone layer depletion:

• Use air condition and refrigerators that do not produce CFC.
• Proper recovery and servicing of vehicles should be done.
• Proper rules and public awareness should be conducted.

Uses of ozone:

• As germicides and disinfectants for purification of water.
• To prepare aldehydes and ketones.
• In oxidizing and bleaching agent.

Some Important Questions

1. What are oxides? Define neutral and mixed oxide with two examples of each?
2. How can you show that ZnO and Al2O3 are amphoteric oxides?
3. Classify the following oxides with reasons: Na2O, MgO, SO3.
4. Give the resonating structure of ozone.
5. What is ozone layer depletion? Suggest its controlling ways.