Helium (He) is a colorless, odorless, tasteless, non-toxic, nearly inert monatomic chemical element that heads the noble gas series in the periodic table and whose atomic number is 2. Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions.

Contents 1 History 2 Sources 3 Properties 4 Uses 5 Applications 6 Helium in the Environment 7 Health effects of helium

[edit] History

Hellium, the lighter of the noble gases, was the first to be discovered. In fact, this element was first identified in the Sun rather than in the Earth. In 1868, during a solar eclipse in India, a spectrometer was used for the first time in the study of the chromosphere around the Sun. The chromosphere's spectrum, among other bright stripes, contain the hydrogen characteristic stripes and a yellow one that, at the time, was thought to be corresponding to sodium. The French astronomer Janssen decided to study the origin of that stripe and tried to reproduce the chromosphere's spectrum starting from ordinary light. He succeeded his purpose proving that the yellow stripe did not belong to sodium, but was probably the stripe of a new element.

Lockyer and Frankland confirmed Janssen's results and proved that the bright yellow stripe could not have an earthly origin. Frankland proposed the name "helium" after the Greek word "Helios" for Sun. This stripe was later detected in spectrums of many other stars and, in 1882, Palmieri observed it in gases erupting from Vesuvius.

The search for this new element in the Earth was not very productive until 1895, when Sir William Ramsay examined a gas produced by a Norwegian ore (cleveite) when treated with acids. In this gas spectrum the bright yellow stripe appeared, proving the existence of hellium on Earth.

Sir William Ramsay made this discovery after the work of Hillebrand, in 1888, that stated that the boiling of uraninite with diluted sulfuric acid produced considerable amounts of an inert gas. He proved that part of this gas was nitrogen, and since helium was not known at the time, he thought that it was only nitrogen. In a letter to Sir William Ramsay, after the discovery of the element, Hillebrand mentioned that he noticed some strange stripes not present in a pure nitrogen spectrum. He did not take this in to account, but only mentioned it to his assistant, loosing in this way the merit of the discovery.

The discovery of hellium in radioactive materials was not totally understood until the discovery of radium in 1898. Then, it was verified that helium was a stable product of the radioactive elements desintegration. This led some scientists to conclude that the hellium present in Earth had that origin. Some others thought that the origin of helium on Earth was a survival of the "primordial helium".

[edit] Sources

Except for hydrogen, helium is the most abundant element found in the universe. Helium is extracted from Natural gas. In fact, all natural gas contains at least trace quantities of helium.

It has been detected spectroscopically in great abundance, especially in the hotter stars, and it is an important component in both the proton-proton reaction and the carbon cycle, which account for the energy of the sun and stars.

The fusion of Hydrogen into helium provides the Energy of the hydrogen bomb. The helium content of the Atmosphere is about 1 part in 200,000. While it is present in various radioactive Minerals as a decay product, the bulk of the Free World's supply is obtained from wells in Texas, Oklahoma, and Kansas. Outside the United States, the only known helium extraction plants, in 1984 were in Eastern Europe (Poland), the USSR, and a few in India.

[edit] Properties

Gaseous chemical element, symbol: He, atomic number: 2 and atomic weight 4,0026 g/mol. Helium is one of the noble gases of group O in the periodic table. It’s the second lightest element. The main helium source in the world is a series of fields of Natural gas in the United States.

Helium is a colourless, odourless, insipid and non-toxic gas. It’s less soluble in water than any other gas. It’s the less reactive element and doesn’t essentially form chemical compounds. The density and viscosity of helium vapour are very low. The termic conductivity and the caloric content are exceptionally high. Helium can be liquefied, but its condensation temperature is the lowest among all the known substances.

[edit] Uses

Helium has many uses even though it is inert. There are three major uses for helium.It is used in low-temperature cooling systems and pressure, lighter-than-air objects and purge systems.

Helium can be very useful in low-temperature cooling because at -270*, or liquid temperature, is able to cool anything because it is so cold. A good example of this as useful is in superconducting devices, because superconducting (electricity can pass from one place to another without wasting any energy) can occur only at very low temperatures.

In pressure systems a gas is used to pressurize the system but the gas is not acceptable if it is able to react with any of the surroundings. Helium is an inert gas that is ideal for these situations. As well, in a purge system an inert gas is used to sweep all gas in a container without reacting with the contents, being inert it is ideal for these situations as well.

Helium is ideal for blimps, balloons and other lighter-than-air crafts because it is neither flammable nor have the lifting effects of Hydrogen, this makes it much safer. Although only used for advertising and other limited purposes, it is an ideal element to make these possible.

Some other common uses for helium include:

• leak detection systems
• welding
• growing silicon and germanium crystals; protective shield
• titanium and zirconium production; protective shield
• nuclear reactors; cooling medium
• diving and others working under pressure; artificial atmosphere with 20% oxygen

supersonic wind tunnels

• cryogenic applications
• liquid fuel rockets; pressurizing
• effecting voice if breathed

[edit] Applications

Helium has many unique properties: low boiling point, low density, low solubility, high thermal conductivity and inertness, so it is use for any application which can explioit these properties. Helium was the first gas used for filling balloons and dirigibles. This application goes on in altitude research and for meteorological balloons. The main use of helium is as an inert protection gas in autogenous welding. Its biggest potential is found in applications at very low temperatures. Helium is the only cooler which is capable of reaching temperatures lower than 15 K (-434ºF). The main application of ultralow temperature is in the development of the superconductivity state, in which the resistance to the electricity flux is almost zero. Other applications are its use as pressurizing gas in liquid propellants for rockets, in helium-Oxygen mixtures for divers, as working fluid in nuclear reactors cooled down by gas and as gas carrier in chemical analysis by gas chromatography.

[edit] Helium in the Environment

Helium is the second most abundant element in the known universe, after hydrogen. Helium constitutes the 23% of all elemental matter measured by mass. Helium is formed in The Earth by natural radioactive decay of heavier elements. Most of this helium migrates to the surface and enters the atmosphere. It could be logical to think that the helium concentration in the Atmosphere was higher than it is (5,25 parts per million at sea level). Nevertheless, its low molecular weight allows it to escape to space at the same rate of its formation. There is an about 1000 km layer in the heterosphere at 600 miles where helium is the dominant gas (although the total pressure is very low). Natural gases contain higher helium concentrations than the Atmosphere. Helium is the 71st most abundant element in the Earth's crust where it is found in 8 parts per billion (109).

[edit] Health effects of helium

Effects of exposure: The substance can be absorbed into the body by inhalation. Inhalation: High voice. Dizziness. Dullness. Headache. Suffocation. Skin: on contact with liquid: frostbite. Eyes: on contact with liquid: frostbite. Inhalation risk: On loss of containment this gas can cause suffocation by lowering the oxygen content of the air in confined areas. Check Oxygen content before entering area.

Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood.