Chemistry

The Discovery of Helium



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Aristotle believed there were only four elements that made up all matter on earth. These elements were earth, air, wind and fire. For thousands of years this was accepted as fact. In the seventeenth century scientists such as Robert Boyle started to question this theory. They put forward the belief that there were many different elements made up of particles called atoms. At the atomic theory gained credence, scientists began looking at the common substances around them to find which were elements and which were compounds or salts of two or more of these elements.

As the number of known elements grew scientific knowledge of the elements physical and chemical properties also grew. One of the properties of elements that was examined was their ability to produce unique spectrographs. Examination of spectrographs from minerals has revealed the presence of many elements that were previously unknown. Many elements, such as samarium and thallium, were found spectroscopically before they could be isolated and identified.

The element helium was also discovered spectrographically but this spectrograph was not from an earth mineral. In 1868 there was an eclipse of the sun. The astronomer Pierre-Jules-Cesar Janssen used this opportunity to examine spectrographs of the sun's corona, He notice a yellow line at 587.49 nanometers which he had not seen before. In consultation with the English astronomer Sir Norman Lockyer he realized that this line was produced by a previously unknown element. The two astronomers believed that the element was only found in the sun and called it helium after the Greek sun god Helios.

The Scottish chemist Sir William Ramsay was experimenting on the uranium containing mineral ore cleveite in 1895. Much of Ramsay's experimental work had been on gases and he had already discovered the noble gases neon, argon, krypton and xenon. His experiments with cleveite also involved the study of gases. He treated the ore with acids and collected samples of the gases produced. He sent these samples to Sir Norman Lockyer and Sir William Crookes who confirmed his suspicions that one of the gases produced was helium.

As often happens, at the same time as Ramsay was producing helium from cleveite two Swedish chemists, Nils Langlet and Per Theodor Cleve, were also experimenting on the mineral. They also found the element helium in cleveite.

Our knowledge of this element has grown over the years. It is the lightest of the noble gases and the second lightest element. It is also the second commonest element in the universe. Only hydrogen, the lightest element is more common than helium.

Although helium is very common in the universe the earth's atmosphere contains only 0.0005% helium. Helium is continually escaping the upper atmosphere into space. It is replaced by the decay of some of the radioactive elements in the earth's crust. The alpha particles produced by alpha decay are helium nuclei. These nuclei can attract two electrons to become helium atoms.

The small amount of helium in air would be a very expensive commercial source of helium. Fortunately helium has been found trapped in underground reservoirs of natural gas and is a byproduct of natural gas extraction.

The gas is inert and has no known compounds. Helium has many uses from inflating party balloons and airships to filling diver's air tanks with a mixture of 80% helium 20% oxygen to prevent nitrogen narcosis.

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