What is helium?
Helium is a colourless, odourless, tasteless inert gas lighter than air - at room temperature and makes up about 0.0005% of the air we breathe
Source?
After hydrogen, helium is the second most abundant element in the universe. It has been detected spectroscopically in great abundance, especially in the hotter stars. It is present in the Earth's atmosphere in about 1 part in 200,000. It is present in various radioactive minerals as a decay product, but the major sources are from wells in Texas, Oklahoma and Kansas
Who discovered Helium?
Helium was first detected by Janssen in 1868 during the solar eclipse as a new line in the solar spectrum, and named by Lockyer and Frankland. It was discovered in the uranium mineral cleveite independently by Ramsay and the Swedish chemists Cleve and Langlet
Helium = Uses
Helium is widely used as an inert gas shield for arc welding; as a protective gas in growing silicon and germanium crystals, and in titanium and zirconium production. It is also used as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels. A mixture of 80% helium and 20% oxygen is used as an artificial atmosphere for divers and others working under pressure. Helium is extensively used for filling balloons as it is a much safer gas than hydrogen. One of the recent largest uses for helium has been for pressurising liquid fuel rockets Helium Flotation - Helium balloons
Helium Balloons work by the law of buoyancy. As long as the helium plus the balloon is lighter than the air it displaces, the balloon will float in the air. Helium is a lot lighter than air. The difference is not as great as it is between water and air (a litre of water weighs about 1,000 grams, while a litre of air weighs about 1 gram), but it is significant. Helium weighs 0.1785 grams per litre. Nitrogen weighs 1.2506 grams per litre, and since nitrogen makes up about 80 percent of the air we breathe, 1.25 grams is a good approximation for the weight of a litre of air. Therefore, if you were to fill a 1-litre soda bottle full of helium, the bottle would weigh about 1 gram less than the same bottle filled with air. That doesn't sound like much -- the bottle itself weighs more than a gram, so it won't float. However, in large volumes, the 1-gram-per-litre difference between air and helium can really add up. This explains why blimps and balloons are generally quite large -- they have to displace a lot of air to float. | | Helium in a Balloon
If you put helium in a balloon and let go of the balloon, the balloon rises until it pops. When it pops, the helium that escapes has no reason to stop -- it just keeps going and leaks out into space. Therefore, in the atmosphere there is very little helium at any given time. The helium that is there comes from alpha particles emitted by radioactive decay. In places that have a lot of uranium ore, natural gas tends to contain high concentrations of helium (up to 7 percent). This makes sense, since the decay of uranium emits lots of alpha particles and a natural gas pocket tends to be a sealed container underground. Helium is cryogenically distilled out of natural gas to produce the helium we put in balloons. What causes helium balloons to lose their lift after a day or two?
In brief, because the helium leaks out, they shrink, and become heavier than the volume of air they displace. This causes them to lose buoyancy and "sink" in the air. The weight balance that keeps a balloon afloat does not leave a lot of room for leakage, so once a little leaks out the balloon falls. Sometimes you can catch a balloon right around the time it is neutrally buoyant, and applying heat (your hand, for instance) or cold (rub with ice cube) will change its volume just enough to make it rise or sink in the air.
Lowest Melting Point
Helium has the lowest melting point of any element and has found wide use in cryogenic research, as its boiling point is close to absolute zero. Its use in the study of superconductivity is vital
Liquid helium (4He) exists in two forms, 4He I and 4He II, above and below 2.174K respectively.
The latter is unlike any other known substance. It expands on cooling, its conductivity for heat is enormous and neither its heat conduction nor viscocity obeys normal rules. It remains liquid down to absolute zero at ordinary pressures, but can readily be solidified by increasing the pressure
Biological Role
Helium has no known biological function, but it is non-toxic.
Helium in the Sun
Helium in the sun is generally believed to be formed by nuclear fusion. This is where nuclei of hydrogen, the lightest element, combine to form helium with huge amounts of energy released. |
