Helium is the lightest element in the group of noble gases. This colorless, odorless, and non-toxic gas sits at the very top of Group 18 on the periodic table, making it the least dense of its chemically similar peers. Its minimal mass is a direct result of its unique atomic structure.
Understanding the Noble Gas Group
The noble gases are a family of elements found in Group 18 of the periodic table, including Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn). These elements are known for their exceptional stability and low chemical reactivity. Their stability stems from having a complete outer electron shell, meaning their atoms have little tendency to gain or lose electrons.
Except for Helium, which only requires two electrons to fill its first shell, all other noble gases possess eight electrons in their outermost shell. This configuration satisfies the octet rule and makes them monatomic gases, meaning they exist as single, unbonded atoms.
Why Helium Is the Lightest Element
An element’s lightness is determined by its atomic mass, the sum of protons and neutrons within the nucleus. Helium has an atomic number of 2, indicating two protons. The most common isotope, Helium-4, also contains two neutrons, resulting in an atomic mass of approximately 4 atomic mass units (amu).
Helium’s minimal nuclear composition establishes it as the lightest noble gas. The next element, Neon, has an atomic number of 10, giving it an atomic mass of about 20 amu. Helium’s tiny nucleus gives it a density significantly lower than air and all other noble gases. Atomic mass generally increases as one moves down the noble gas group.
Where Helium Comes From and How It Is Used
The Helium found on Earth is continuously generated underground, rather than being a primordial component. It is created through the natural radioactive decay of heavy elements, primarily uranium and thorium, which emit alpha particles (Helium-4 nuclei). This radiogenic Helium accumulates and becomes trapped in natural gas reserves, sometimes reaching concentrations as high as 7% by volume.
Helium’s unique properties, such as its extremely low boiling point of -268.9 degrees Celsius, make it indispensable for high-technology applications. Its largest use is in cryogenics, specifically as a coolant for the superconducting magnets used in Magnetic Resonance Imaging (MRI) machines. Liquid Helium cools these magnets to near absolute zero, allowing them to operate effectively.
Beyond advanced cooling, Helium is known for its lifting capabilities in balloons and airships. Unlike hydrogen, Helium is non-flammable, making it a safer choice for lighter-than-air craft. It is also mixed with oxygen to create breathing mixtures for deep-sea divers, as its low solubility helps prevent decompression sickness.