تويت
Carbon is one of the chemical elements. Along with hydrogen, nitrogen, oxygen, phosphorus, and sulfur, carbon is a building block of biochemical molecules ranging from fats, proteins, and carbohydrates to active substances such as hormones. All carbon atoms have a nucleus containing six protons. Ninety-nine percent of these also contain six neutrons. The 6 proton + 6 neutron atoms are said to have a mass of 12 and are referred to as "carbon-12." The nuclei of the remaining one percent of carbon atoms contain not six but either seven or eight neutrons in addition to the standard six protons. They have masses of 13 and 14 respectively and are referred to as "carbon-13" and "carbon-14."
If two atoms have equal numbers of protons but differing numbers of neutrons, one is said to be an "isotope" of the other. Carbon-13 and carbon-14 are thus isotopes of carbon-12. Isotopes participate in the same chemical reactions but often at differing rates. When isotopes are to be designated specifically, the chemical symbol is expanded to identify the mass (for example, 13C).
Both 13C and 14C are present in nature. The former accounts for about 1% of all carbon. The abundance of 14C varies from 0.0000000001% (one part per trillion, a small, but measurable, level) down to zero. The highest abundances of 14C are found in atmospheric carbon dioxide and in products made from atmospheric carbon dioxide (for example, plants). Unlike 12C and 13C, 14C is not stable. As a result it is always undergoing natural radioactive decay while the abundances of the other isotopes are unchanged. Carbon-14 is most abundant in atmospheric carbon dioxide because it is constantly being produced by collisions between nitrogen atoms and cosmic rays at the upper limits of the atmosphere.
If two atoms have equal numbers of protons but differing numbers of neutrons, one is said to be an "isotope" of the other. Carbon-13 and carbon-14 are thus isotopes of carbon-12. Isotopes participate in the same chemical reactions but often at differing rates. When isotopes are to be designated specifically, the chemical symbol is expanded to identify the mass (for example, 13C).
Both 13C and 14C are present in nature. The former accounts for about 1% of all carbon. The abundance of 14C varies from 0.0000000001% (one part per trillion, a small, but measurable, level) down to zero. The highest abundances of 14C are found in atmospheric carbon dioxide and in products made from atmospheric carbon dioxide (for example, plants). Unlike 12C and 13C, 14C is not stable. As a result it is always undergoing natural radioactive decay while the abundances of the other isotopes are unchanged. Carbon-14 is most abundant in atmospheric carbon dioxide because it is constantly being produced by collisions between nitrogen atoms and cosmic rays at the upper limits of the atmosphere.
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