Nonmetallic chemical element; symbol C. → Atomic number 6; → atomic weight 12.011; → melting point about 3,550°C; → boiling point 4,827°C. The most abundant isotope of carbon is 12C. Carbon is one of the most important elements for life. The burning of carbon in the form of coal and oils has been essential in the development of industrial societies. It is the element that hardens → steel and the sole element in → diamonds. The carbon in nature is produced inside massive stars. → triple-alpha process; → Hoyle state.
Carbon, from Fr. carbone, coined by Antoine Lavoisier (1743-1794) to distinguish it from charbon (Fr.) "charcoal," from L. carbo (genitive carbonis) "a coal, charcoal."
Fr.: combustion du carbon
The stage in the evolution of a star after → helium burning
when the core of the star consists mainly of carbon and oxygen. In stars of mass
greater than about 8 solar masses, whose cores reach a temperature above
5 × 108 K and density above 3 × 109 kg m-3,
carbon burning can begin via reactions such as the following:
Fr.: crise du carbone
A problem raised in the past by observations suggesting that the amount of carbon necessary for standard → dust models was larger than what actually observed for the → interstellar medium (ISM) (Snow & Witt 1995). The problem was especially acute for the → 2175 A bump in the ultraviolet part of the → extinction curve. The so-called "crisis" was finally solved by, on the one hand, revising downward the → solar abundances, thought to represent the ISM abundances (Asplund et al. 2009, arXiv:0909.0948, and references therein), and, on the other hand, revising upward the ISM carbon abundances (Sofia et al., 2011, AJ 141, 22S).
carxe-ye karbon (#)
Fr.: cycle du carbone
1) A complex series of processes through which all the carbon atoms on
Earth is cycled through the air, ground, plants, animals, and fossil
fuels. During the cycle, plants absorb → carbon dioxide
(CO2) from the atmosphere and through
→ photosynthesis incorporate the associated
carbon atoms into sugars and other molecules necessary for
growth. Plants return carbon atoms back to the atmosphere in the form
of CO2. However, much of the carbon absorbed remains "locked up" in
the living organisms until decomposition or fire releases it back to
dioksid-e karbon, gâz karbonik (#)
Fr.: dioxyde de carbone
CO2, also called carbonic acid gas. A colorless gas which occurs in
the atmosphere playing an essential part in animal respiration and the
growth of green plants. → photosynthesis,
→ carbon cycle. It is formed by the
→ oxidation of carbon and carbon compounds. Carbon dioxide is the most
important → greenhouse gas produced by human activities, primarily
through the combustion of fossil fuels. Its concentration in the
Earth's atmosphere has risen by more than 30% since the Industrial
Revolution. CO2 forms a solid at -78.5 °C at atmospheric pressure, and
is used as a refrigerant in this form as a dry ice for the
preservation of frozen foods. As carbon dioxide gas is heavier than
air and does not support combustion, it is used in fire
carbon monoxide (CO)
monoksid-e karbon (#)
Fr.: monoxyde de carbone
A colorless, odorless, very poisonous gas which burns in air with a
bright blue flame to form → carbon dioxide.
CO gives rise to a violent explosion when ignited in air in certain proportions. It
occurs in coal gas and in the exhaust fumes of motor engines. Melting point -207 °C;
boiling point -191.1 °C.
Fr.: étoile carbonée
A radioactive isotope of carbon, whose nucleus contains 6 protons and 8 neutrons; also called → radiocarbon. 14C is naturally produced in the atmosphere when a neutron created by a cosmic ray hits the nucleus of an atom of nitrogen-14. The nucleus absorbs the neutron and ejects a proton, thereby transforming itself into 14C. It decays back to nitrogen, with a half-life is 5730 years, after emitting an electron (146C → 147N + e- + νe). See also → radiocarbon dating.
carbon-enhanced metal-poor star (CEMP)
setâre-ye kamfelez-e karbon bolandidé
Fr.: étoile pauvre en métaux enrichie en carbon
A star that presents very low → iron → abundances [Fe/H] < -4 but an → anomalous richness in carbon. CEMP stars have been defined as a subset of → metal-poor stars that exhibit elevated [C/Fe] ≥ +1.0. It has been recognized that ~15-20% of stars with [Fe/H] < -2.0 are carbon enhanced. This fraction rises to 30% for [Fe/H] < -3.0, to 40% for [Fe/H] < -3.5, and ~75% for [Fe/H] < -4.0. This increasing trend of CEMP-star frequency with declining [Fe/H] is confirmed by the observation of many thousands of CEMP stars (Daniela Carollo + ApJ 2014, 788, 180). See also → extremely metal-poor star (EMPS)
Containing or composed of carbon.
From → carbon + -aceous, from L. -aceus "-ous."
Karboni, adj. from karbon, → carbon; karbondâr "having carbon," with -dâr "having, possessor," from dâštan "to have, to possess;" O.Pers./Av. root dar- "to hold, keep back, maintain, keep in mind;" cf. Skt. dhr-, dharma- "law;" Gk. thronos "elevated seat, throne;" L. firmus "firm, stable;" Lith. daryti "to make;" PIE base *dher- "to hold, support."
Fr.: chondrite carbonée
A rare type of → stony meteorite having a higher → carbon content than other classes of meteorite. They represent only ~5% of the known meteorites. Their bulk composition is mainly → silicates, → oxides and sulfides, whilst the minerals → olivine and serpentine are characteristic. The six classes of carbonaceous chondrites are: → CI chondrites, CM chondrites, CV chondrites, CO chondrites, CK chondrites, CR chondrites, CH chondrites, and CB chondrites.
goruh-e karbonil (#)
Fr.: groupe carbonyl
The radical -C=O, which occurs in several compounds, such as → aldehydes and ketones.
Hidrokarbon, loan from Fr.
polycyclic aromatic hydrocarbons (PAHs)
hidrocarburhâ-ye aromâtik-e polisiklik, ~ ~ bol-carxe-yi
Fr.: hydrocarbures aromatiques polycycliques
1) Chemistry: A family of → organic molecules composed
of carbon and hydrogen atoms (→ hydrocarbons) in which
→ carbon atoms appear in multiple loops (polycyclic)
with strong chemical → bonds that exist between them (aromatic).
PAHs are formed during the incomplete burning of coal, oil and gas, garbage, or other
organic substances like tobacco or charbroiled meat. As a pollutant, they are of
concern because some compounds (benzo(a)pyrene) have been identified as tending to
senn yâbi-ye partow-karboni
Fr.: datation au radiocarbone
A radioactive dating technique, applied to organic materials, which measures the content of the radioactive isotope of carbon 14C. The radioactive carbon isotopes created by the impact of cosmic rays with the nitrogen atoms of the atmosphere find their way, via carbon dioxide and photosynthesis, into living material. When an organic material dies it ceases to acquire further 14C atoms, and its 14C fraction declines at a fixed exponential rate due to the radioactive decay of 14C. Comparing the remaining 14C fraction of a sample to that expected from atmospheric 14C allows the age of the sample to be estimated.
singly ionized carbon
Fr.: carbone une fois ionié
A carbon atom → singly ionized by a photon of energy 11.3 eV. The ion C+ emits a → fine-structure line (2P3/2→ 2P1/2) at 157.7 μm when excitation conditions are satisfied (critical density ~ 3 x 103 cm-3). In → photodissociation regions, [C II] 157.7 μm is a major cooling line for regions exposed to significant → far ultraviolet (FUV) photon fluxes. In Galactic → H II regions, as well as in the central regions of external galaxies, the luminosity of the [C II] line is typically ~ 0.05-0.5% of the FUV luminosity and correlates well with → carbon monoxide (CO) line intensities.