Noble gases are gaseous elements and are also known as rare gases as these are of low amount in the atmosphere.
They are called noble gases because of their chemical inertness.
The noble gases are: helium, neon, argon, krypton, xenon and radon.
Radon, of course, is not present in the atmosphere. However, it is produced in the radioactive decay of radium.
Helium is present in sun’s atmosphere as well as in natural gas up to maximum of 10%.
Noble gases are colourless and odourless and are exclusively used as inert atmosphere in welding and cutting, inside electric bulbs and in metallurgical operation.
In liquefied form, the natural gases are used for creating low temperature.
Halogens are the four elements fluorine, chlorine, bromine and iodine.
Fluorine and chlorine are gases, bromine is a violatile liquid and iodine is a volatile solid.
Halogens are highly reactive.
They do not occur in nature in Free State but only as compounds.
Their colours are :
- Fluorine – Pale yellow
- Chlorine – Yellowish green
- Bromine – Reddish brown or Orange
- Iodine – Violet black
It is widely used in drinking water supply as germicide.
It is also used for manufacturing bleaching powder, disinfectants, hydrochloric acid and many organic compounds.
It is a non – metallic element. It burns with a blue flame emitting sulphur dioxide.
It occurs in many allotropic forms, as the elements in many volcanic regions and as sulphides of many metals.
It is employed in vulcanizing rubber, manufacturing of dyes and chemicals in medicines and for killing moulds as well as pests.
It is necessary for life. It too occurs in many allotropic forms, mainly as calcium phosphate.
White phosphorus is very inflammable and poisonous solid. Its compounds are employed as fertilizers and detergents.
It is a non – metal, found abundantly in earth’s crust and sand and in rocks as silica or silicates.
Semi – Conductors are made of pure elements of silicon. As silicates, it is widely used for manufacturing glass. It is also used in alloys.
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