2. Helium Properties and Applications

Helium, the second element on the periodic table, is a versatile noble gas with a unique history and a wide array of applications. Let’s discuss a brief history, physical and chemical properties, applications, uses, and recent Advancements and helium conservation efforts.

The Discovery of Helium: A Brief History

Helium was first discovered not on Earth, but in the cosmos. This unique element was identified in 1868 by two scientists, French astronomer Jules Janssen and British scientist Norman Lockyer. The discovery occurred during a solar eclipse when Janssen and Lockyer observed an unknown bright yellow spectral line in the Sun’s chromosphere.

This spectral line did not match any known elements on Earth, leading Lockyer to propose the existence of a new element, which he named helium after the Greek word “Helios,” meaning the Sun. Helium thus became the first element discovered extraterrestrially before being found on Earth.

In 1895, Sir William Ramsay, a Scottish chemist, isolated helium on Earth while studying uranium-bearing minerals such as cleveite. He noticed that heating the minerals released a gas that exhibited the same spectral lines as the helium observed in the Sun. Almost simultaneously, scientists Per Teodor Cleve and Nils Abraham Langlet independently isolated helium from uranium ores in Sweden, confirming Ramsay’s findings.

The discovery of helium not only unveiled a new element but also expanded our understanding of the Sun’s composition and deepened our grasp of spectroscopy’s potential to explore the universe.

3D Electron Configuration of helium and its isotopes

Here is s 3D Structure of the helim isotopes for better understanding and visualization. Select the isotopes from the dropdown menu, the 3d structure with electron cloud will appear automatically.

An Overview of Helium's Properties

Physical Properties of Helium

Helium is a colourless, odourless, tasteless gas under standard conditions. It is the lightest noble gas and second only to hydrogen in atomic mass and density. Helium exhibits unique physical properties due to its quantum mechanical nature.

1. State and Phase Behaviour

Helium exists as a monoatomic gas at standard temperature and pressure (STP). It remains gaseous over an extensive temperature range. Helium transitions to a liquid state at temperatures near absolute zero and does not solidify under standard atmospheric pressure.

Critical Temperature: −267.96 °C (5.2 K)
Critical Pressure: 0.227 MPa (2.27 atm)

Under normal pressures, helium remains a superfluid in its liquid state down to absolute zero. It solidifies only at pressures exceeding approximately 2.5 MPa (25 atm) and temperatures below 1 K.

2. Boiling and Melting Points

Helium has the lowest melting and boiling points of all the known substances:

Boiling Point: −268.93 °C (4.22 K)
Melting Point: Solidifies at approximately 0.95 K under high pressure (>25 atm).

These extreme phase transition temperatures make helium indispensable for cryogenics and low-temperature physics.

3. Density and Atomic Mass

Atomic Mass: 4.002602 u
Density at STP: 0.1786 g/L

Liquid helium at its boiling point has a density of 0.125 g/cm³, significantly less than that of most liquids.

4. Thermal conductivity and Heat Capacity

Helium is an excellent thermal conductor and has a high specific heat capacity, especially in its liquid state. These properties make helium highly effective as a coolant for superconducting magnets and other cryogenic applications.

Thermal Conductivity (gas at STP): 0.1513 W·m⁻¹·K⁻¹
Specific Heat (gas at constant pressure): 20.79 J·mol⁻¹·K⁻¹

In its superfluid state, helium exhibits zero viscosity and extraordinary thermal conductivity, enabling phenomena such as the fountain effect.

5. Solubility and Diffusion

Helium has an extremely low solubility in water and other liquids, with Henry’s law constant of approximately 8.61 × 10⁻⁴ mol·kg⁻¹·atm⁻¹ at 298 K. Its small atomic size and low viscosity allow it to diffuse through materials more readily than most gases, making it a preferred choice for leak detection.

6. Refractive Index and Non-Polar Nature

Helium has the lowest refractive index of any gas (approximately 1.000035 at 589 nm wavelength). Its non-polar nature results in negligible van der Waals forces.

Chemical Properties of Helium

Helium is a noble gas (Group 18) with a full outer electron shell, rendering it chemically inert under most conditions.

1. Electronic Structure and Stability

Electron Configuration: 1s²: Helium’s filled 1s orbital ensures maximum stability, minimizing its tendency to participate in chemical reactions.

2. Reactivity

Helium is non-reactive under standard conditions and does not form conventional chemical bonds. Its first ionization energy is 24.587 eV, the highest among all elements, making it extremely difficult to ionize.

3. Helium Compounds

Although helium does not naturally form compounds, a few have been synthesized under laboratory conditions:

Van der Waals Complexes: Weakly bound interactions with other molecules (e.g., He·H₂, He·N₂).
Ionic Compounds: Under extreme pressures, helium can form clathrate-like structures, such as Na₂He, stabilized by trapped helium atoms.

These compounds are rare and exist only under specific experimental conditions, such as pressures above 1 million atmospheres.

4. Isotopes of Helium

Helium has two stable isotopes, helium-3 (³He) and helium-4 (⁴He), along with several unstable isotopes that are observed under specific conditions in nuclear physics experiments.

Stable Isotopes

Helium-4 (⁴He)
Helium-3 (³He)

Helium-4 (⁴He)

Helium-4 (⁴He): Helium-4 accounts for over 99.99% of helium found on Earth. It consists of 2 protons, 2 neutrons, and 2 electrons.Helium-4 was produced in vast quantities during the BIG BANG nucleosynthesis and continually formed through the radioactive decay of heavy elements like uranium and thorium in the Earth's crust.

Applications of Helium-4

Helium-4 is used in cryogenics, particularly as liquid helium for cooling superconducting magnets in MRI machines and particle accelerators.
It is a key component in studies of superfluidity at low temperatures.

Helium-3 (³He)

Helium-3 (³He) constitutes only about 0.0001% of natural helium. It contains 2 protons, 1 neutron, and 2 electrons and is stable due to its low neutron-proton ratio.

Origin

• Primordial helium-3 was formed during the Big Bang.
• Continually produced through nuclear reactions in stars.
• Detected in trace amounts in Earth's mantle and the lunar regolith.

Applications of Helium-3

• Essential for low-temperature physics and cryogenics.
• Used as a neutron detector in scientific and security applications.
• Studied as a potential fuel for future nuclear fusion reactors.

Helium-3 and the Future of Energy

Helium-3 has been proposed as a potential fuel for nuclear fusion reactors due to its ability to produce energy with minimal radioactive byproducts. Lunar mining missions have been suggested as a method to extract helium-3 from the Moon’s regolith, potentially enabling a clean energy revolution in the future.

Unstable Isotopes of Helium

Helium also has several radioactive isotopes, all of which are highly unstable with short half-lives:

Helium-5 (⁵He):

• Contains 2 protons and 3 neutrons.
• Decays rapidly via neutron emission.
• Studied in nuclear physics for its role in particle reactions.

Helium-6 (⁶He):

• Contains 2 protons and 4 neutrons.
• Half-life: ~0.8 seconds.
• Undergoes beta decay, emitting an electron and an antineutrino.

Helium-7 (⁷He) and Helium-8 (⁸He):

• Exotic isotopes with very short lifetimes (<10⁻²⁰ seconds for ⁷He).
• Known as neutron-rich isotopes and exist momentarily during high-energy particle collisions.

Uses and Applications of Helium

Helium’s unique physical and chemical properties enable a wide range of applications across diverse industries:

1. Healthcare and Medical Applications

• MRI Machines: Helium’s cryogenic properties cool superconducting magnets in MRI scanners, ensuring precise imaging.
• Respiratory Therapy: Helium-oxygen mixtures (Heliox) are used to alleviate respiratory distress in patients with obstructive airway conditions.

2. Cryogenics

Liquid helium is the primary coolant for:

• Superconductors: Used in research facilities, such as the Large Hadron Collider (LHC).
• Quantum Computing: Cooling quantum processors to near-absolute zero temperatures for stable operation.

3. Aerospace and Space Exploration

Helium is critical for:

• Rocket Propulsion: Used to pressurize and purge fuel tanks.
• Spacecraft Leak Detection: Due to its low atomic mass, helium easily escapes through small leaks, allowing for precise testing.

4. Industrial and Manufacturing Uses

• Welding Shield Gas: Provides an inert atmosphere for welding aluminium, stainless steel, and titanium.
• Semiconductor Manufacturing: Used as a carrier gas in lithography and etching processes.

5. Scientific Research

• Particle Physics: Helium is used in bubble chambers to track high-energy particles.
• Low-Temperature Experiments: Superfluid helium enables studies on quantum mechanics and phase transitions.

6. Entertainment and Buoyancy: Party Balloons and Airships: Helium’s non-flammable nature and low density make it ideal for buoyant applications.

7. Leak Detection Systems: Helium’s small atomic size and high diffusivity make it a reliable tracer gas for detecting leaks in high-pressure systems, pipelines, and vacuum environments.

Recent Discoveries and Research

Helium in Exoplanets

Helium has been detected in the atmospheres of distant exoplanets, providing insights into planetary formation and evolution. Advanced telescopes like the James Webb Space Telescope have contributed to these findings.

Helium-3 in Fusion Energy

Helium-3 is being studied as a potential fuel for clean and sustainable nuclear fusion. Research focuses on harvesting it from lunar regolith or through artificial isotopic enrichment.

Helium Nanotechnology

Helium ions are increasingly used in nanotechnology for precise imaging and etching in semiconductor manufacturing, enabling the creation of smaller and more efficient microchips.