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Helium
Helium, with the atomic number 2, is located on the upper right side of the periodic table. It is the most abundant noble gases and holds the top position among them.
1.0Introduction
Helium, with the chemical symbol He and atomic number 2, is the lightest noble gas and element in Group 18 of the periodic table. In terms of chemical abundance, it is second only to hydrogen in the cosmos. At -268°C, helium is a tasteless, colourless, and odourless gas or liquid. Due to its lightness, helium is relatively scarce in Earth's atmosphere. It also has the lowest freezing and boiling points of any known substance in the universe, and under normal air pressure, it cannot be solidified through cooling alone.
The element's name was derived from the Greek word "Helios," meaning "Sun," after scientists discovered helium in the Sun before it was found on Earth. Lockyer and Frankland proposed the name due to the element's presence in the solar atmosphere, which was identified through its spectral lines.
2.0Occurrence and Isotopes of Helium
Helium is 24% of the universe's elemental mass, mainly found in the Sun and Jupiter. Helium-4, formed during the Big Bang, is the most common isotope, with helium-3 and helium-4 present in Earth's atmosphere at a ratio of nearly 1,000,000:1.
Helium has eight isotopes, with helium-3 (³He) and helium-4 (⁴He) being stable. Helium-6 is the longest-lived radioisotope, and helium-3 is more abundant in the interstellar medium, up to 100 times higher than on Earth.
3.0Physical Properties of Helium
4.0Helium Ion (He⁺)
Helium ions, such as He⁺, are created in mass spectrometers when an energetic electron collides with a helium atom in a high-vacuum environment. Magnetic and electric fields prevent the resulting He⁺ ions from adhering to the vessel walls, allowing them to travel toward the detector.
Under controlled pressure conditions (around 10⁵ mm Hg), a He⁺ ion may interact with a neutral helium atom to form a He²⁺ ion. Due to their high bond energy and a chemical bond order of 0.5, these ions can only exist in a vacuum.
5.0Chemical Properties of Helium
- Reactivity: Helium is highly unreactive. It does not react with water and is less soluble in water. It is non-flammable and does not react with oxygen.
- Inertness: Helium is the least reactive noble gas, making it one of the least reactive elements. It is chemically inert and remains monatomic under normal conditions.
- Thermal Conductivity and Diffusion: Helium has high thermal conductivity, specific heat, and sound speed in its gas phase—surpassed only by hydrogen. Due to its small atomic size, it diffuses through materials at a rate three times higher than air and 65% faster than hydrogen.
- State of Matter: When cooled, helium condenses into liquid helium. It is the only element that cannot solidify under normal pressure, regardless of temperature.
6.0Uses of Helium
Among its most common applications, helium is primarily utilised in altitude research and meteorological balloons.
- Helium is an inert protective gas in autogenous welding, preventing the weld from melting.
- Helium is the only known cooler capable of achieving temperatures below 15K (-434°F).
- It also produces germanium, silicon crystals, and other specialised applications.
- In industry, helium is used for pipeline leak detection due to its ability to diffuse through solids much faster than air.
- Helium is also used in gas chromatography as a carrier gas.
- Given its low melting point, liquid helium has numerous applications in fields such as cryogenics, magnetic resonance imaging (MRI), and superconducting magnets.
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