# Get the Knowledge that sets you free...Science and Math for K8 to K12 students

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## Oxygen Family

Is oxygen the reason for our death after 100 years? Billions of years ago there was very less proportion of oxygen on Earth. The primitive organisms lived without oxygen through anaerobic metabolism. Later when the photosynthesis was invented there was a threat for these anaerobic organisms. They struggled for existence and evaluated into the present aerobic organisms (human beings are aerobic animals). How they survived with this toxic content? Is oxygen really toxic? Yes, the toxic oxygen is the reason even for the death of human beings about 100 years.

Oxygen necessary for metabolic reactions and it is necessary for combustion of fuels to get energy. But due to the reactive oxygen species (ROS) such as, super oxide and peroxide radicals which are released as by products of metabolism, our body cell membranes slowly decay and it will take an average of 100 years for the total impairment of organs (death). However, smoking, pollution, radiation etc decrease the average lifespan by increasing the ROS concentration.

## After completing the topic, the student will be able to:

• List elements in oxygen family.
• Write the electronic configuration of group 16 elements.
• Give the details of occurrence and abundance of elements of group 16.
• Discuss the individual properties of group 16(VIA) elements.
• Examine the allotropism shown by elements of group 16.
• Describe the physical and chemical properties of compounds of group 16 elements.
• Examine the irregular trends in properties of compounds of group 16 elements.
• Discuss in detail about properties of oxygen and sulfur.
• List the series of oxyacids of sulfur and write their structures.
• Give the preparation, properties and uses of sulfuric acid.
Elements of the Group 16 The first element of this Group, oxygen, is the only gas, and is colorless and odorless. Sulfur is a pale yellow, brittle solid. Selenium can have either an amorphous or a crystalline structure; the amorphous form can be red or black, and the crystalline form can be red or gray. Tellurium is a silvery–white color with a metallic luster. Polonium is a naturally radioactive element.
Oxygen Family

Group 16 elements [Oxygen family]
Oxygen and sulfur along with selenium and tellurium are the four non‐metals and polonium (metal) belonging to Group 16 and are collectively called as chalcogens or ore‐forming elements, because many metal ores are oxides or sulfides. Chalcogens have six electrons in their outermost energy levels, one electron less than the halogens and two electrons less than the noble gases and hence they function as electron acceptors. The elements of this family are :O, S, Se, Te, Po. Mnemonic: Oliver Smith Sells Tea Pots.

Electronic configuration
All the elements have six electrons in their outermost shell, i.e., they have electronic structure s2p4. The penultimate shell contains 2 electrons in oxygen, 8 electrons in sulfur and 18 electrons in Se, Te and Po. This explains why oxygen differs from sulfur and these two form the remaining elements.

The other elements Se, Te, and Po are very scarce.
Occurrence of oxygen

Oxygen is the most abundant of all elements. It exists in the free form as dioxygen molecules O2 and makes up 20.9% by volume and 23% by weight of the atmosphere. Most of this has been produced by photosynthesis, the process where the chlorophyll in the green parts of plants uses the sun's energy to make foodstuffs such as glucose sugar.

6CO2 + 6H2O + energy from the sun C6H12O6 + 6O2

Oxygen makes up 46.6% by weight of the earth's crust, where it is the major constituent of silicate minerals. Oxygen also occurs as many metal oxide ores, and as deposits of oxosalts such as carbonates, sulfates, nitrates and borates. Oceans cover three quarters of the earth's surface, and oxygen makes up 89% by weight of the water in the oceans. Ozone O3 exists in the upper atmosphere and is of great importance.

Sulfur is the sixteenth most abundant element and constitutes 0.034% by weight of the earth's crust. It occurs mainly in the combined form as numerous sulfide ores, and as sulfates (particularly gypsum CaSO4.2H2O). It is not economic to mine these to obtain S, although gypsum is mined for other uses. The native element can be obtained from volcanic sources in many places, but these sources are little used now except in Japan and Mexico. From Biblical times up till the present century volcanic sources provided the major source of S. In early times S in the form of brimstone (burning rock) was used for fumigation. From the thirteenth century until the middle of the nineteenth century it was used to make gunpowder. In the present century the major use has been to make H2SO4.