Chemistry

The Inert Gas Helium



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Helium is an element that occurs as a gas at standard temperature and pressure. It is an inert gas, which means that it is, for all practical purposes, not chemically reactive.  One atom of helium has two protons, two neutrons and two electrons, filling its outer atomic shell.  Helium was first isolated in 1895 in London by the Scottish chemist William Ramsay. The name “helium” comes from the Greek word helios, which means sun.

Helium is colorless, odorless and tasteless.  Its boiling and melting points are the lowest of all elements and cannot exist in any phase other than gas except in the most extreme conditions.  However, at temperatures close to absolute zero, helium condenses to a liquid with some very interesting properties.  It becomes what is known as a “superfluid” with almost no viscosity, or thickness.  As a result, it will actually climb up the sides of its container.  

Helium is the second most abundant element in the universe after hydrogen. Together, hydrogen and helium make up 98% of all the matter in the Earth’s solar system.  It makes up about 23 percent of all the matter in the entire universe.  However, there is not much helium left on earth.  Because of its light weight, most of it has been lost, and nearly all that remains is the result of radioactive decay.  Helium is mined commercially from natural gas deposits, mostly from Texas, Oklahoma and Kansas.  

Because of its lightness and inertness, helium has many practical applications.  One of its most important uses is in magnetic resonance imaging, or MRI, a diagnostic imaging tool used in medical facilities to diagnose illness and to assess injuries.  MRI machines use a huge superconducting magnet to produce a magnetic field.  A great deal of heat is generated in the process, and liquid helium is used to regulate the temperature of the magnets.  Because there is no suitable substitute for helium for this purpose, a shortage of helium could affect the availability of MRI and its use in health care.

Helium and other inert gases are also used in welding.  Because it is non-reactive, it protects metals from oxidation at the high temperatures of welding. 

Hydrogen is the only other gas that is lighter in weight than helium.  Hydrogen was once used in blimps because of its lightness, but because of its reactivity, the results were disastrous.  Helium use in blimps and dirigibles was its most important application until the end of World War II.  Today, it is still used in balloons.

Since helium atoms are so small and since the element has very low viscosity, it is hard to contain.  For this reason, it is an excellent choice for leak detection.  It is used to test high vacuum and fuel systems and other sorts of containments.

Heliox is a mixture of helium and oxygen that is lighter than air.  It is sometimes used in intensive care units as a breathing mixture because it creates a reduction in resistance to flow within the airways. This reduces the work of breathing in patients with conditions that are characterized by increased airway resistance, such as asthma, COPD (chronic obstructive pulmonary disease) and upper airway obstructions. 

Many people have been amused by the high-pitched, squeaky voice created by inhaling helium gas. Sound waves travel at different speeds through gases of different densities.  The more dense the gas, the more slowly the sound waves travel, and the lighter the gas, the faster they travel.  Helium is lighter than air, so when it is inhaled, the sound waves of speech travel much faster through the vocal cords than they would when air is inhaled, resulting in a higher-pitched sound.  Caution should be exercised when inhaling helium because the lack of oxygen can result in fainting. 

The supply of helium on earth has been built up over billions of years from the decay of radioactive uranium and thorium.  However, this decay takes place at a very slow rate.  Some of the helium produced in this manner is trapped in natural gas deposits, but because it is so lightweight, the earth’s gravity does not hold it well, and when it is released into the atmosphere, it drifts off into space.  Since helium’s uses are many , especially in science and technology, the element is being used up more quickly than it is reoccurring, and so it is considered a nonrenewable resource whose supply is in danger.  

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