Science, Tech, Math › Science Helium Facts (Atomic Number 2 or He) Chemical & Physical Properties of Helium Print scanrail / Getty Images Science Chemistry Periodic Table Basics Chemical Laws Molecules Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. Learn about our Editorial Process Updated on September 02, 2021 Helium is atomic number 2 on the periodic table, with the element symbol He. It is a colorless, flavorless gas, best known for its use in filling floating balloons. Here is a collection of facts about this lightweight, interesting element: Helium Element Facts Helium Atomic Number: 2 Helium Symbol: He Helium Atomic Weight: 4.002602(2) Helium Discovery: Janssen, 1868, some sources say Sir William Ramsey, Nils Langet, P.T. Cleve 1895 Helium Electron Configuration: 1s2 Word Origin: Greek: helios, sun. Helium was first detected as a new spectral line during a solar eclipse, so it is named for the Greek Titan of the Sun. Isotopes: 9 isotopes of helium are known. Only two isotopes are stable: helium-3 and helium-4. While the isotopic abundance of helium varies depending on geographical location and source, 4He accounts for nearly all of the natural helium. Properties: Helium is a very light, inert, colorless gas. Helium has the lowest melting point of any element. It is the only liquid that cannot be solidified by lowering the temperature. It remains liquid down to absolute zero at ordinary pressures, but can be solidified by increasing the pressure. The specific heat of helium gas is unusually high. The density of helium vapor at the normal boiling point is also very high, with the vapor expanding greatly when heated to room temperature. Although helium normally has a valence of zero, it has a weak tendency to combine with certain other elements. Uses: Helium is widely used in cryogenic research because its boiling point is near absolute zero. It is used in the study of superconductivity, as an inert gas shield for arc welding, as a protective gas in growing silicon and germanium crystals and producing titanium and zirconium, for pressuring liquid fuel rockets, for use in magnetic resonance imaging (MRI), as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels. A mixture of helium and oxygen is used as an artificial atmosphere for divers and others working under pressure. Helium is used for filling balloons and blimps. Sources: Except for hydrogen, helium is the most abundant element in the universe. It is an important component in the proton-proton reaction and the carbon cycle, which account for the energy of the sun and stars. Helium is extracted from natural gas. In fact, all natural gas contains at least trace quantities of helium. The fusion of hydrogen into helium is the sources of a hydrogen bomb's energy. Helium is a disintegration product of radioactive substances, so it is found in ores of uranium, radium, and other elements. Most of Earth's helium dates back to the planet's formation, although a small amount falls to Earth within cosmic dust and some is produced via beta decay of tritium. Read More 10 Helium Facts By Anne Marie Helmenstine, Ph.D. Compounds: Because a helium atom has a valence of zero, it has extremely low chemical reactivity. However, unstable compounds called excimers can be formed when electricity is applied to the gas. HeH+ is stable in its ground state, but it is the strongest known Bronsted acid, capable of protonating any species it encounters. Van der Waals compounds form with cryogenic helium gas, such as LiHe. Element Classification: Noble Gas or Inert Gas Usual Phase: gas Density (g/cc): 0.1786 g/L (0 °C, 101.325 kPa) Liquid Density (g/cc): 0.125 g/mL (at its boiling point) Melting Point (°K): 0.95 Boiling Point (°K): 4.216 Critical Point: 5.19 K, 0.227 MPa Atomic Volume (cc/mol): 31.8 Ionic Radius: 93 Specific Heat (@20°C J/g mol): 5.188 Heat of Fusion: 0.0138 kJ/mol Evaporation Heat (kJ/mol): 0.08 First Ionizing Energy (kJ/mol): 2361.3 Lattice Structure: Hexagonal Lattice Constant (Å): 3.570 Lattice C/A Ratio: 1.633 Crystal Structure: close-packed hexagonal Magnetic Ordering: diamagnetic CAS registry number: 7440-59-7 Quiz: Ready to test your helium facts knowledge? Take the Helium Facts Quiz. References Meija, J.; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305 Shuen-Chen Hwang, Robert D. Lein, Daniel A. Morgan (2005). "Noble Gases". Kirk Othmer Encyclopedia of Chemical Technology. Wiley. pp. 343–383. doi:10.1002/0471238961.0701190508230114.a01. Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4. Return to the Periodic Table Cite this Article Format mla apa chicago Your Citation Helmenstine, Anne Marie, Ph.D. "Helium Facts (Atomic Number 2 or He)." ThoughtCo, Sep. 2, 2021, thoughtco.com/helium-facts-606542. Helmenstine, Anne Marie, Ph.D. (2021, September 2). Helium Facts (Atomic Number 2 or He). Retrieved from https://www.thoughtco.com/helium-facts-606542 Helmenstine, Anne Marie, Ph.D. "Helium Facts (Atomic Number 2 or He)." 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