Helium (He)
Stable isotopes of helium available from ISOFLEX
| Isotope | Z(p) | N(n) | Atomic Mass | Natural Abundance | Enrichment Level | Chemical Form |
| He-3 | 2 | 1 | 3.016029309 | 0.000134% | ≥99.80% | Gas |
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The first evidence of helium was observed in 1868 by French astronomer Pierre-Jules-César Janssen during a solar eclipse in Guntur, India. Later that same year, English astronomer Norman Lockyer observed a similar yellow line in the solar spectrum. He and English chemist Edward Frankland named the element with the Greek word helios, meaning “sun.” Scottish chemist Sir William Ramsay isolated helium on Earth for the first time in 1895.
Helium is the second most abundant element in the universe (although rare on Earth). It is a colorless, odorless gas that is also very slightly soluble in water, while being insoluble in ethanol. It is inert and monatomic in all standard conditions. Due to the small size of helium atoms, its diffusion rate through solids is three times that of air and around 65% that of hydrogen. No stable chemical compounds are known.
Helium-3 is used as a circulating medium in laboratory refrigerators to maintain constant temperatures below 3º K. Helium is also used as a lifting gas in buoyant airships and in most types of balloons, such as weather-, toy-, kite-type- and advertising balloons. Its lifting power is just slightly less than that of hydrogen. In nuclear physics, helium ions or alpha particles serve as projectiles in bombarding heavy nuclei to produce energy or to obtain artificial radioisotopes. Liquid helium is used in magnetic resonance imaging (MRI) equipment for the diagnosis of cancer and other soft-tissue diseases.
Properties of Helium
| Name | Helium |
| Symbol | He |
| Atomic number | 2 |
| Atomic weight | 4.0026 |
| Standard state | Gas |
| CAS Registry ID | 7440-59-7 |
| Group in periodic table | 2 |
| Group name | Noble gas |
| Period in periodic table | 1 |
| Block in periodic table | s-block |
| Color | Colorless |
| Classification | Noble gas |
| Melting point | -272.2 °C |
| Boiling point | -268.93 °C |
| Thermal conductivity | 0.1513 W/(m·K) |
| Heat of vaporization | 0.083 kJ·mol-1 |
| Heat of fusion | 0.02 kJ·mol-1 |
| Density of gas | 0.1785 g/L at 0 ºC and 1 atm |
| Density of liquid | No data available |
| Electron configuration | 1s2 |
| Atomic radius | 0.33 Å |
| Oxidation state | 0 |
| Critical temperature | -267.96 ºC |
| Critical pressure | 2.24 atm |
| Critical volume | 57 cm3/mo |
| Refractive index | 1.000036 at 0 ºC and 1 atm |
| Solubility in water |
0.0285 mg/L (calculated) at 25 ºC |
Research
- Use of hydrochemistry, stable isotope, radiocarbon, 222Rn and terrigenic 4He to study the geochemical processes and the mode of vertical leakage to the Gambier Basin Tertiary Confined Sand Aquifer, South Australia
- High-sensitivity measurement of 3He-4He isotopic ratios for ultracold neutron experiments
- Primordial helium entrained by the hottest mantle plumes
- Efficient generation of energetic ions in multi-ionplasmas by radio-frequency heating
- Thermonuclear reactions probed at stellar-core conditions with laser-based inertial-confinement fusion
- High-Precision Measurement of the Proton’s Atomic Mass
- Gas fields show carbon storage is secure
- Primordial and recycled helium isotope signatures in the mantle transition zone