 | |
| General | |
|---|---|
| Symbol | 12C |
| Names | carbon-12 |
| Protons(Z) | 6 |
| Neutrons(N) | 6 |
| Nuclide data | |
| Natural abundance | 98.93%[1] |
| Isotope mass | 12Da |
| Spin | 0 |
| Excess energy | 0.0keV |
| Binding energy | 92161.753±0.014 keV |
| Parent isotopes | 12N 12B |
| Isotopes of carbon Complete table of nuclides | |
Carbon-12 (12C) is the most abundant of the twostableisotopes of carbon (carbon-13 being the other), amounting to 98.93% ofelementcarbon on Earth; its abundance is due to thetriple-alpha process by which it is created in stars. Carbon-12 is of particular importance in its use as the standard from whichatomic masses of allnuclides are measured, thus, its atomic mass is exactly 12daltons by definition. Carbon-12 is composed of 6protons, 6neutrons, and 6electrons.
Seecarbon-13 for means of separating the two isotopes, thereby enriching both.
Before 1959, both theIUPAP andIUPAC usedoxygen to define themole; 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 theoxygen-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 theCIPM (International Committee for Weights and Measures) in 1967, and in 1971, it was adopted by the 14thCGPM (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] consistently with the above definition of the mole.
In 1980, the CIPM clarified the above definition, defining that the carbon-12 atoms are unbound and in theirground state.
In 2018, IUPAC specified the mole as exactly6.02214076×1023 "elementary entities". The number of moles in 12 grams of carbon-12 became a matter of experimental determination.
TheHoyle state is an excited, spin-0,resonant state of carbon-12. It is produced via thetriple-alpha process and was predicted to exist byFred Hoyle in 1954.[3] The existence of this 7.7 MeV resonance is essential for thenucleosynthesis of carbon in helium-burningstars and predicts an amount of carbon production 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 ahelium-4 nucleus fuses with aberyllium-8 nucleus in a high-temperature (108 K) environment with densely concentrated (105 g/cm3) helium. As a consequence of the short half-life of8Be, two helium nuclei fusing into it must be followed within ~10−16 seconds by a third, forming carbon. The Hoyle state also is a short-lived resonance with a half-life of2.4×10−16 s; it primarily decays back into its three constituentalpha particles, though 0.0413% of decays (or 1 in 2421.3) occur by emission ofgamma rays into the ground state of12C.[5]
In 2011, anab initio calculation of the low-lying states of carbon-12 found (in addition to theground andexcited spin-2 state) a resonance with all of the properties of the Hoyle state.[6][7]
| Lighter: carbon-11 | Carbon-12 is an isotope ofcarbon | Heavier: carbon-13 |
| Decay product of: boron-12,nitrogen-12 | Decay chain of carbon-12 | Decays to: stable |