Bob Durham, age 10, of Greensburg, Ky., for his question:
What Elements are present in the air?
Our filmy atmosphere is thickest at the surface of the Earth. As we go up, it becomes thinner until it finally merges with the plasma as space. It is a mixture of assorted gases. And the widest assortment of gaseous elements is in the lowest level of air around us at ground level.
The atoms in a chemical Element are all alike. Twin atoms of oxygen often form molecules, but the substance remains an Element because all its atoms are alike. The molecules of a chemical compound are made of assorted atoms. A molecule of carbon dioxide has one atom of the element carbon and two of the element oxygen. The bulk of any sample of the air around us is made up mostly of the gaseous elements nitrogen and oxygen, but this is not nearly the whole story.
More than 78% of the gaseous air is nitrogen and almost 21% is oxygen. If we separate the gasses in 10 quarts of ordinary air, we get nearly eight quarts of nitrogen and about two of oxygen. About 1% of the mixture is argon gas. The remaining fraction will include traces of the gaseous elements neon and krypton, xenon and helium, plus some gaseous molecules of water vapor and a few of the compound carbon dioxide.
In some samples we may find a few molecules of methane or ammonia, carbon dioxide or hydrogen sulphide. There may be traces of nitrous oxide and in air near the oceans there will be traces of ozone. Under certain conditions, the solids and liquids of the Earth become gases. Their atoms and molecules then become separate particles of matter and often go off to mingle with the other gases of the air. In some samples of air, there may be gaseous particles of iron or almost any of the other countless substances normally found on the Earth as solids or liquids.
In addition to the gaseous elements, there are also fragments of solid materials fine enough to float in the air. It is hard to imagine the tiny size of atoms and molecules. In a cubic inch of air, there are about 300 billion billion of these single, gaseous particles. Among them may be 15,000 to 5 million fine fragments of dust and sooty smoke, scraps of salt and other chemicals, assorted seedlets and pollens, various germs and midget microbes. In even a small sample of ordinary air, we may find a few atoms and molecules of almost all of the 90 odd elements that make up the solid and liquid substances of the Earth.
The gaseous water vapor and small specks of floating solids find their way back to the Earth and other such particles go off to replace them in the air. A small percentage of the atmosphere is made up of elements that change from day to day and from place to place. This may include fragments, either solid or gaseous, of almost any of the Earth’s natural elements. Meantime, the bulk of the air's gases remain more or less the same all around the Earth. Almost all of it is made from the two gaseous Elements nitrogen and oxygen.