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Carbon-12 is of particular importance in its use as the standard from which atomic masses of all nuclides are measured, thus, its atomic mass is exactly 12 daltons by definition. Carbon-12 is composed of 6 protons , 6 neutrons , and 6 electrons .
Carbon is a constituent (about 12% by mass) of the very large masses of carbonate rock (limestone, dolomite, marble, and others). Coal is very rich in carbon (anthracite contains 92–98%) [64] and is the largest commercial source of mineral carbon, accounting for 4,000 gigatonnes or 80% of fossil fuel. [65]
For comparison, the atomic mass of a carbon-12 atom is exactly 12 daltons. Alternately, the atomic mass of a carbon-12 atom may be expressed in any other mass units: for example, the atomic mass of a carbon-12 atom is 1.992 646 882 70 (62) × 10 −26 kg. As is the case for the related atomic mass when expressed in daltons, the relative ...
The densities of the carbon group elements tend to increase with increasing atomic number. Carbon has a density of 2.26 g·cm −3; silicon, 2.33 g·cm −3; germanium, 5.32 g·cm −3; tin, 7.26 g·cm −3; lead, 11.3 g·cm −3. [13] The atomic radii of the carbon group elements tend to increase with increasing atomic number.
The mass number gives an estimate of the isotopic mass measured in atomic mass units (u). For 12 C, the isotopic mass is exactly 12, since the atomic mass unit is defined as 1/12 of the mass of 12 C. For other isotopes, the isotopic mass is usually within 0.1 u of the mass number.
An example of use of a mass number is "carbon-12," which has 12 nucleons (six protons and six neutrons). The actual mass of an atom at rest is often expressed in daltons (Da), also called the unified atomic mass unit (u). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately 1.66 × 10 −27 ...
The molar mass constant, usually denoted by M u, is a physical constant defined as one twelfth of the molar mass of carbon-12: M u = M(12 C)/12. [1] The molar mass of an element or compound is its relative atomic mass (atomic weight) or relative molecular mass (molecular weight or formula weight) multiplied by the molar mass constant.
The atomic mass of different isotopes ... The ratio of carbon-13 and carbon-12 ... This variability can be used for approximate determination of geographic location ...