- Helium was discovered 150 years ago in 1868 by French astronomer Pierre Janssen during a solar eclipse using spectroscope.
- Helium is the second-lightest and second most common element in the universe after hydrogen gas.
- Helium belongs to the group of noble gases that occupy the far right hand side of the periodic table.
- It is the most unreactive (inert) element in the periodic table.
- Low chemical reactivity is due to a stable electron arrangement (filled outer shell of electrons).
Helium in our solar system
- Helium is a major component of Sun’s atmosphere.
- It is not abundant on earth because Earth’s gravity is not strong enough to hold a light element like helium.
- Helium is a major component of the gas giants like Jupiter and Saturn as they are bigger planets with stronger gravity.
Helium on Earth
- Helium was discovered on Earth inside cleveite which is a uranium-based mineral.
- Helium is mostly trapped beneath the surface of the earth in radioactive rocks of uranium and thorium.
- As uranium and thorium decay, they release alpha particles which are nothing but helium nucleus.
- These alpha particles mop up electrons and make helium.
Important properties of Helium
- Helium is a very stable element being chemically inert and nonreactive.
- It is nonflammable and nonpoisonous.
- Most importantly, it boils at 4.2 Kelvin, or minus 268 degrees Celsius which is the lowest temperature possible in the universe.
- No other element can remain a liquid at these temperatures.
Super conductors and Helium:
- Materials that conduct electricity well such as metals are called conductors.
- The electrons flow inside a metal with some friction. This friction is called resistance.
- Superconductors are conductors that have zero resistance .i.e. they don’t impede electricity at all.
- However, all known superconductors have the zero resistance property only at low temperatures.
- The original superconductors are kept cold by immersing them in liquid helium.
Significance in MRI and NMR:
- The key to magnetic resonance imaging and nuclear magnetic resonance is producing enormous magnetic field to image the human body.
- The electric resistance in materials makes it difficult to generate a large magnetic field which requires high electrical currents.
- This is possible only by superconductors kept at ultra-low temperatures for which liquid helium is essential.
Magnetic Cooling technology and Helium:
- Magnetic cooling technology could make fridges and air conditioners quieter, safer and more environmentally friendly.
- Traditional cooling systems which use compressor-cooling technology will account for 13 percent of the entire world’s greenhouse gas emission by 2030.
- Magnetic cooling requires extremely low temperatures which is possible with liquid helium.
Other Industrial applications:
- Aerospace and defense technologies, high-tech manufacturing, rocket engine testing, welding, commercial diving, magnets in particle accelerators, the production of fiber optic cables and semiconductor chips found in cell phones