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Helium (He)

QUICK REFERENCE

  • Symbol: He
  • Atomic Number: 2
  • Atomic Weight: 4.002602(2)
  • Element Classification: Noble gas
  • Discovered By: Pierre Janssen and Joseph Norman Lockyer
  • Discovery Date: 1868 (observed during a solar eclipse)
  • Name Origin: From the Greek word “helios” (sun)
  • Density: 0.1786 g/L at 0°C and 1 atm (Gas phase)
  • Melting Point: -272.20°C (-457.96°F; 0.95 K under pressure)
  • Boiling Point: -268.928°C (-452.070°F; 4.222 K)
  • Appearance: Colorless gas
  • Atomic Radius: 31 pm
  • Atomic Volume: 31.8 cm³/mol
  • Covalent Radius: 28 pm (estimated)
  • Ionic Radius: Not applicable for a noble gas
  • Specific Heat: 5.193 J/(g·K) at 20°C (Gas phase)
  • Fusion Heat: Not defined (Helium does not solidify at standard pressure)
  • Evaporation Heat: 0.0845 kJ/mol
  • Thermal Conductivity: 0.1513 W/(m·K)
  • Pauling Negativity Number: Not applicable (Helium is chemically inert)
  • First Ionizing Energy: 2372.3 kJ/mol
  • Oxidation States: 0 (Helium is inert and does not form compounds under normal conditions)
  • Electronic Configuration: 1s²
  • Lattice Structure: Hexagonal Close-Packed (HCP) when solidified under extreme conditions

Discovery

Helium was first detected as a yellow spectral line in sunlight during a solar eclipse in 1868 by Jules Janssen and Norman Lockyer, who mistakenly believed it to be sodium. They named the element after the Greek word ‘helios’, meaning sun. It wasn’t until 1895 that helium was found on Earth by Sir William Ramsay, Per Teodor Cleve, and Nils Abraham Langlet, who discovered it in the mineral cleveite, thus proving its existence outside the sun.

Relation to Other Elements

Helium is the second element in the periodic table and is part of the noble gases group, which are known for their lack of chemical reactivity due to their full valence electron shell. It stands out among the noble gases for having the lowest boiling and melting points, which is a consequence of its closed-shell electron configuration. This configuration makes helium very stable and inert, rarely forming compounds with other elements.

Natural Occurrence

Helium is the second most abundant element in the universe, primarily produced through the nuclear fusion of hydrogen in stars. On Earth, helium is relatively rare in the atmosphere and is mostly obtained from natural gas fields where it has accumulated from the radioactive decay of heavy elements over millions of years.

Uses

Helium has several important applications, including:

  • Cryogenics: Its low boiling point makes it ideal for cooling superconducting magnets in MRI machines and other cryogenic applications.
  • Gas for Balloons and Airships: Helium is used in balloons and airships because it is non-flammable and lighter than air, making it a safe and effective lifting gas.
  • Protective Atmospheres: In welding and in the production of silicon wafers for electronics, helium is used as a protective gas to prevent oxidation.
  • Leak Detection: Due to its small atomic size, helium is used in leak detection for high-vacuum systems and gas pipelines.
  • Breathing Mixtures: Helium is mixed with oxygen to create breathing gases for deep-sea diving and medical treatments, as it prevents nitrogen narcosis.

Helium’s discovery story intertwines with our understanding of the sun and marked a significant moment in the study of the universe. Its unique properties and applications have made it an invaluable element in science and industry.

Hydrogen (H)

The Creation Story from the Book of Genesis