Helium.
From the Greek helius (sun). It was discovered in the solar spectrum. Discovered in 1868 by astronomers Janssen (French) and Lockeyer (English), in the solar spectrum. On Earth, it was first detected by Ramsay, in 1895, in the vicinity of uranium minerals.
After hydrogen, it is the most abundant element, a stable product of nuclear fusion that occurs in the sun and stars. On Earth it is found in a small amount in the air (4.6 ppm in volume) and in some natural gases. Participates with only 0.004 ppm by weight of the earth's crust.
Applications:
He in discharge tubes used in illuminated advertisements. Metal arc welding in helium atmosphere. Coolant in nuclear reactors. Breathing gas (80% He and 20% O2) for diving and therapeutic purposes. Balloons and airships.
Helium compounds are not known.
Periodic Properties Table:
Atomic Mass: 4.0026 u
Density (25 ºC): 0.179 g / L (CNTP)
Ionization Energy: 2370 kJ / mol
Melting Point: -272.2 ºC (26 atm)
Boiling Point: -268.9 ºC
Atomic Radius: 50 pm
Electronegativity: (Unknown)
