2 · He
Helium
Observed in the solar spectrum in 1868 by Janssen and Lockyer, isolated on Earth by Ramsay in 1895.
Identity
- Atomic number
- 2
- Symbol
- He
- Canonical name
- Helium
- Category
- noble gas
- Group
- 18
- Period
- 1
- Block
- s
Properties
These quantities come from the Periodic Table JSON compilation. They have not yet been checked, one by one, against CIAAW atomic weights or NIST measurements. A value marked estimated is not a measurement.
- Atomic mass
- 4.002602 u
- Electron configuration
- 1s2
- Electrons per shell
- 2
- Standard state
- gas
- Density
- 0.1786 g/L
- Melting point
- 0.95 K The listed melting point applies under pressure: helium does not freeze at atmospheric pressure.
- Boiling point
- 4.222 K
- First ionization energy
- 2,372.3 kJ/mol
- Electron affinity
- -48 kJ/mol
History
Solar line observed
Observation · jointly credited · 1868
Janssen observes an unknown yellow line in the solar chromosphere spectrum.
Line assigned to a solar element
Observation · jointly credited · 1868
Lockyer assigns the same line to an element then unknown on Earth.
Terrestrial isolation
Isolation · confirmed · 1895
Ramsay isolates helium from uranium minerals. The 1868 solar observation was not this isolation.
Etymology
- Theme
- celestial body
- Language
- grec
- Root
- helios
- Meaning
- the sun
Named for the solar line, before terrestrial isolation.
Scientists
Places and institutions
- London — historical setting : United Kingdom — present country : United Kingdom
See also
Sources
- IUPAC, Periodic Table of the Elements
- Bowserinator, Periodic Table JSON. Compilation secondaire d’où viennent les grandeurs physiques importées (masse, densité, températures, énergies). Elles ne sont pas revérifiées une à une auprès du NIST ou de la CIAAW.
- John Emsley, Nature’s Building Blocks: An A–Z Guide to the Elements