Carbon-12

Source: Wikipedia, the free encyclopedia.
For the building in Oregon, see Carbon12.
Carbon-12, 12C
12B
Isotopes of carbon
Complete table of nuclides

Carbon-12 (12C) is the most abundant of the two

electrons
.

History

Before 1959, both the

IUPAC used oxygen to define the mole; the chemists defining the mole as the number of atoms of oxygen which had mass 16 g, the physicists using a similar definition but with the oxygen-16
isotope only. The two organizations agreed in 1959–60 to define the mole as follows.

Mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 12 gram of carbon 12; its symbol is "mol".

This was adopted by the

CGPM (General Conference on Weights and Measures)
.

In 1961, the isotope carbon-12 was selected to replace oxygen as the standard relative to which the atomic weights of all the other elements are measured.[2]

In 1980, the CIPM clarified the above definition, defining that the carbon-12 atoms are unbound and in their ground state.

In 2018, IUPAC specified the mole as exactly 6.02214076×1023 "elementary entities". The number of moles in 12 grams of carbon-12 became a matter of experimental determination.

Hoyle state

The Hoyle state and possible decay ways

The Hoyle state is an excited, spinless, resonant state of carbon-12. It is produced via the triple-alpha process and was predicted to exist by Fred Hoyle in 1954.[3] The existence of the 7.7 MeV resonance Hoyle state is essential for the nucleosynthesis of carbon in helium-burning stars and predicts an amount of carbon production in a stellar environment which matches observations. The existence of the Hoyle state has been confirmed experimentally, but its precise properties are still being investigated.[4]

The Hoyle state is populated when a helium-4 nucleus fuses with a beryllium-8 nucleus in a high-temperature (108 K) environment with densely concentrated (105 g/cm3) helium. This process must occur within 10−16 seconds as a consequence of the short half-life of 8Be. The Hoyle state also is a short-lived resonance with a half-life of 2.4×10−16 s; it primarily decays back into its three constituent alpha particles, though 0.0413% of decays (or 1 in 2421.3) occur by internal conversion into the ground state of 12C.[5]

In 2011, an ab initio calculation of the low-lying states of carbon-12 found (in addition to the ground and excited spin-2 state) a resonance with all of the properties of the Hoyle state.[6][7]

Isotopic purification

The isotopes of carbon can be separated in the form of carbon dioxide gas by cascaded chemical exchange reactions with amine carbamate.[8]

See also

References

  1. ^ "Table of Isotopic Masses and Natural Abundances" (PDF). 1999.
  2. ^ "Atomic Weights and the International Committee — A Historical Review". 2004-01-26.
  3. ISSN 0067-0049
    .
  4. doi:10.1016/j.ppnp.2014.06.001
    .
  5. hdl:1885/101943
    .
  6. S2CID 33827991
    .
  7. doi:10.1103/Physics.4.38
    .
  8. doi:10.1016/j.energy.2006.04.002
    .

External links


Lighter:
carbon-11
 		Carbon-12 is an
isotope of carbon 		Heavier:
carbon-13
nitrogen-12
 Decay chain
of carbon-12 		Decays to:
stable
Retrieved from "https://en.wikipedia.org/w/index.php?title=Carbon-12&oldid=1212343504"