| Symbol | He |
| Atomic number | 2 |
| Group | 18 (Noble gases) |
| Period | 1 |
| Block | s |
| Classification | Noble Gas |
| Appearance | Colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field |
| Color | Colorless |
| Number of protons | 2 p+ |
| Number of neutrons | 2 n0 |
| Number of electrons | 2 e- |
| Phase at STP | Gas |
| Density | 0.1786 g/cm3 |
| Atomic weight | 4.0026 u |
| Melting point | 0.95 K -272.2 °C -457.96 °F |
| Boiling point | 4.222 K -268.928 °C -452.0704 °F |
| Heat of vaporization | 0.0845 kJ/mol |
| Electronegativity (Pauling Scale) | - |
| Electron affinity | -48 kJ/mol |
| Oxidation states | 0 |
| Ionization energies |
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| Discovery | Pierre Janssen, Norman Lockyer (1868) |
| First isolation | William Ramsay, Per Teodor Cleve, Abraham Langlet (1895) |
| Named by | Edward Frankland, Norman Lockyer (1868) |
Discovery of helium Helium was first detected as an unknown, yellow spectral line signature in sunlight during a solar eclipse in 1868 by Georges Rayet, Captain C. T. Haig, Norman R. Pogson, and Lieutenant John Herschel, and was subsequently confirmed by French astronomer Jules Janssen during a total solar eclipse in Guntur, India. Janssen is often jointly credited with detecting the element, along with Norman Lockyer. Janssen recorded the helium spectral line during the solar eclipse of 1868, while Lockyer observed it from Britain. Lockyer was the first to propose that the line was due to a new element. Lockyer and English chemist Edward Frankland named the element with the Greek word for the Sun, ἥλιος (helios). The formal discovery of the element was made in 1895 by chemists Sir William Ramsay, Per Teodor Cleve, and Nils Abraham Langlet, who found helium emanating from the uranium ore, cleveite, which is now not regarded as a separate mineral species, but as a variety of uraninite. | |