Air envelopes the entire surface of Earth. It is invisible, tasteless and has no smell. Air extends great distances above the Earth. One half of the air, by weight, is within 5.63 km of the earth’s surface. The other half is spread over hundreds of kilometres beyond that.
Air is essential for life. No living being – plant or animal – can survive without it. It gives us energy and plants get their food from the carbon dioxide present in it.
What is air? It is a mixture of various gases – oxygen, nitrogen, carbon dioxide, inert gases (helium, neon, argon etc.) and water vapours etc. It contains 78% nitrogen, 21% oxygen, and 1% other gases.
First of all, oxygen helps in burning. If there is no oxygen in the air, nothing will burn. Nitrogen, too, is a very useful gas. Molecular nitrogen is inert because of the strong triple bond between the two atoms, but it will react with some elements, especially the alkaline-earth metals, to give nitrides; with oxygen, and hydrogen. On the other hand, activated nitrogen, formed in an electric discharge, consists of nitrogen atoms and is much more reactive. Nitrogen compounds in the form of fertilizers are very useful for trees and plants. Carbon dioxide is used by plants for breathing. The water vapours in the air help to produce rain. The quantity of water vapour in the air varies from place to place. It determines the amount of rainfall at a place.
As we go up the Earth’s surface, the pressure of the air decreases. The atmospheric pressure at the mountains is less because the molecules of air are separated from each other by larger distances. Therefore air is light there. This is why mountaineers need extra oxygen for breathing and carry oxygen cylinders with them.
