Dec 12 2012
Pierre-Jules-César Janssen, a French astronomer first observed the yellow line spectrum during the solar eclipse in 1868. Sir Norman Lockyer, an English astronomer, realized that no known element at that time could be responsible for the line of wavelength 587.49 nm and hence named the unknown element as helium. In 1895, Sir William Ramsay, a Scottish scientist performed a spectroscopic examination of cleveite containing uranium and exposed it to mineral acids. The resulting gas samples were sent to scientists Sir William Crookes and Lockyer, and they identified the presence of helium in clevite.
Basic Information
| Name |
Helium |
| Symbol |
He |
| Atomic number |
2 |
| Atomic weight |
4.0026 amu |
| Standard state |
gas at 298 K |
| CAS Registry ID |
7440-59-7 |
| Group in periodic table |
18 |
| Group name |
Noble gas |
| Period in periodic table |
1 |
| Block in periodic table |
p-block |
| Color |
Colorless |
| Classification |
Non-metallic |
| Melting point |
0.95 K (-272.2°C or -458°F) |
| Boiling point |
4.22 K (-268.93°C or -452.07°F) |
| Density |
0.00017 g/cm3 |
| Phase at room temperature |
Gas |
Occurrence
Although helium is relatively scarce on earth, it is the second most abundant element in the universe. Around 11.3% of atoms in the universe are helium atoms. Traces of helium are present in the atmosphere, and the air we breath constitutes about 0.000524% of helium. However, it is hard to evaluate the quantity of helium present in the Earth's crust as the gas quickly escapes into the air.
Isotopes
Helium has eight isotopes with mass numbers from 3 to 10 out of which two are naturally occurring stable isotopes-helium-3 and helium-4 with respective proportions of 0.0001% and 99.999%. Helium also has three short-lived radioactive isotopes.
Production
Helium can be obtained by heating monazite sands at 1000°C (1832°F). It can also be produced by liquefaction of natural gas deep under the Earth's crust. The gas is mostly recovered from the natural gas deposits of Kansas, Oklahoma and Texas for commercial use.
Health Aspects
Certain health effects of helium gas upon inhalation are listed below:
- Headache
- Suffocation
- Dullness
- Dizziness
- High voice.
Key Properties
The key properties of helium are listed below:
- It is an odorless, colorless, tasteless inert gas
- It has the lowest melting point of all elements
- It has a boiling point close to 0K
- It does not solidify at 0K under normal pressures, but remains a liquid due to superfluidity
- It does not react with any element as it is chemically inert.
Applications
Some of the major applications of helium include the following:
- Diving gas mixtures
- Filling balloons and other light aircrafts
- Refrigerant for superconductors
- Semiconductor manufacture and welding purposes
- Cooling MRI scanners
- Pressure and purge systems
- Leak-detection systems
Sources and Further Reading