The discovery of helium dates back to a series of 19th-century scientific breakthroughs. While most people recognize helium today as the gas that produces voice-altering effects when inhaled, its scientific importance extends far beyond this trivial application. This article will systematically examine helium’s properties, historical discovery, and modern applications.
Properties of Helium
Helium was produced during the Big Bang nucleosynthesis process along with hydrogen and lithium. As the second most abundant element in the universe, helium constitutes approximately 23% of all baryonic matter. In stellar cores, helium is continuously produced through nuclear fusion reactions.
Although trace amounts of helium exist in the human body, it serves no known biological function. Similarly, helium is found in various concentrations (measured in ppt, ppm, and ppb) within Earth’s crust, atmosphere, and seawater.
| Symbol | He |
| Atomic Number | 2 |
| Atomic Mass | 4.002602 |
| Melting Point | – 272°C (0.95K) at 26 atm |
| Boiling Point | -269°C (4.2K) |
| Density | 0.18 g /L |
| Group | 18 |
| Physical State at 273 K | Gas |
| Configuration | 1s2 |
| Reactivity | Inert |
Helium is an odorless and colorless gas that exhibits several unique characteristics:
- Flammability & Density: It is non-flammable and possesses lower density than air
- Toxicity: While non-toxic and generally harmless to humans in normal conditions, it may pose risks in certain circumstances
- Atomic Properties:
- Highest ionization energy among all elements
- Atomic radius of 1.4 Å (angstroms)
- Extremely low chemical reactivity (reluctance to form bonds)
Isotopic Composition
Helium exists in two stable isotopic forms:
- ³He (helium-3) – rare isotope
- ⁴He (helium-4) – predominant natural form (99.9999% abundance
Source:Wikicommons
For more detailed information, you may look for the NIST database or PubChem.
The Discovery of Helium: A Remarkable Story
The discovery of helium has a fascinating history, dating back to the late 1800s. In 1870, during the Franco-Prussian War, the Prussian army had completely besieged Paris with 2.5 million people residing in Paris. Amid this blockade, only one man was granted an exemption and the freedom to leave: Jules Janssen, a French astronomer. The Germans, prioritizing science over war, offered him this privilege.
However, Janssen surprised them by refusing the offer—he could not abandon his people after months of siege by taking the easy way out. Instead, he boldly declared that he would fly over the blockade in a hot-air balloon.
The Germans reluctantly acquiesced to Janssen’s balloon proposal, though they warned they would shoot him down as a spy upon landing – no idle threat, given their prior actions against others. Yet the astronomer proceeded undeterred.
Jules Janssen Source: Photograph of Jules Janssen by Nadar, 1892 (History of Photography Archive on Flickr)
Janssen’s resolve stemmed from his solar eclipse observations in India two years prior, where he had employed atomic spectroscopy – a technique that had already facilitated the discovery of numerous elements. Each element in the periodic table produces characteristic spectral lines resembling a unique barcode pattern.
During the eclipse, a critical astronomical phenomenon occurred: while the Moon obscured the Sun’s photosphere, the solar corona remained visible. This granted Janssen seven precious minutes of darkness for spectroscopic analysis. His initial observations revealed:
- The distinctive spectral signature of hydrogen
- The characteristic yellow sodium D-line emission
Source: Spectrum Analysis in Its Application to Terrestrial Substances, and the Physical Constitution of the Heavenly Bodies, 1872.
Upon closer examination, Janssen noticed something peculiar. While the sodium doublet (D-line) typically appears around 589 nm in laboratory conditions, the spectral lines he observed during the eclipse were slightly shifted to just below 588 nm – a mere one nanometer difference (equivalent to one billionth of a meter). This minute discrepancy deeply troubled him and prompted further investigation. Although cloud cover initially prevented immediate follow-up observations, he successfully replicated the finding the following day. Over the next month, he meticulously documented these anomalous readings and submitted his observations to the French Academy of Sciences in Paris. While uncertain of their exact significance, he recognized their potential importance.
Remarkably, that same year, English astronomer Norman Lockyer made parallel discoveries. Unlike his counterpart, Lockyer was convinced he had identified a new element and promptly submitted his findings to the same French institution. By extraordinary coincidence, both scientists’ reports arrived on the same day, with each receiving due credit for the discovery. Drawing from Greek mythology, Lockyer proposed naming the element “helium” (from Helios, the Sun god), as its spectral signature had first been detected in solar observations rather than terrestrial samples.
The Completion of Helium’s Discovery: A Scientific Odyssey
In 1870, despite the Prussian siege of Paris, Janssen sought to conduct further eclipse observations—this time in Algeria—to gather more data. However, he had underestimated one formidable adversary: Otto von Bismarck. True to his earlier threat, Bismarck vowed to shoot down the astronomer’s balloon, declaring that the stars Janssen would see on this journey would be his last. Yet against all odds, Janssen prevailed, escaping the blockade to continue his research.
Initially, Janssen’s colleagues dismissed his findings, with some even ridiculing them. Many believed helium existed only in the Sun—until 1882, when Italian physicist Luigi Palmieri detected the same yellow spectral lines in lava emitted by Mount Vesuvius. This marked the first terrestrial evidence of helium, debunking its exclusivity to the Sun.
The experimental confirmation of helium came through Sir William Ramsay, the renowned discoverer of multiple noble gases. While processing cleveite (a uranium ore) with sulfuric acid to isolate argon, Ramsay encountered an anomalous gas. Spectroscopic analysis—verified by Lockyer—revealed an exact match to the solar helium lines observed decades earlier. Key milestones:
- Royal Society Publication: Ramsay’s work was published in the Proceedings of the Royal Society of London (1895).
- Independent Isolation: Swedish chemists Per Teodor Cleve and Abraham Langlet soon extracted helium from cleveite, cementing its discovery.
Though not mentioned earlier, Gustav Kirchhoff’s foundational work on spectroscopy (from 1865) paved the way for these breakthroughs. The collective efforts of Kirchhoff, Janssen, Lockyer, Ramsay, Cleve, and Langlet culminated in helium’s formal identification—a triumph of international collaboration.
Applications of Helium
Helium exhibits diverse applications across multiple scientific, industrial, and commercial sectors due to its unique physicochemical properties. The principal uses include:
1. Medical Imaging
- Liquid helium serves as a cryogenic coolant for superconducting magnets in Magnetic Resonance Imaging (MRI) systems, enabling high-resolution anatomical visualization.
2. Nuclear Technology
- Functions as an inert coolant in nuclear reactors, preventing overheating while maintaining neutron moderation efficiency.
3. Aerospace & Diving
- Lighter-than-air gas: Fills meteorological/surveillance balloons and airships (non-flammable alternative to hydrogen).
- Deep-sea diving: Mixed with oxygen (heliox) to prevent nitrogen narcosis during saturation diving.
4. Cryogenics & Superconductivity
- Essential for cooling superconducting magnets in particle accelerators (e.g., LHC) and quantum computing systems.
5. Industrial Manufacturing
- Welding & metal fabrication: Provides an inert shielding gas (e.g., in TIG welding) to prevent oxidation.
- Leak detection: Tracer gas for identifying micro-leaks in pipelines/vacuum systems.
6. Commercial Applications
- Barcode scanners: Neon-helium lasers (632.8 nm) enable precise retail scanning.
- Rocket propulsion: Pressurizes fuel tanks and purges cryogenic systems in space launch vehicles.
References:
- Emsley, J. (2011). Nature’s building blocks: An A-Z guide to the elements (New ed.). Oxford University Press. https://doi.org/10.1093/acprof:oso/9780199605637.001.0001
- Science History Institute. (2023, May 18). The High-Flying, Death-Defying Discovery of Helium. https://www.sciencehistory.org/stories/magazine/the-high-flying-death-defying-discovery-of-helium/
- This month in Physics history. (n.d.). American Physical Society. https://www.aps.org/archives/publications/apsnews/201409/physicshistory.cfm
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