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2He4.003
Helium
Noble GasHelium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among all the elements.
Phase: GasAppearance: colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
2
Physical Properties
Atomic Mass4.0026022 u
Density0.1786 g/cm³
Melting Point0.95 K
Boiling Point4.222 K
Period1
PhaseGas
Chemical Properties
Electron Configuration1s2
Semantic Config1s2
Shells2
Electron Affinity-48 kJ/mol
Ionization Energies
IE1: 2372.3 kJ/molIE2: 5250.5 kJ/mol
Discovery
Discovered byPierre Janssen