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Natural iron (26 Fe) consists of four stable isotopes: 5.845% 54 Fe (possibly radioactive with half-life > 4.4 × 10 20 years), [4] 91.754% 56 Fe, 2.119% 57 Fe and 0.286% 58 Fe. There are 28 known radioisotopes and 8 nuclear isomers, the most stable of which are 60 Fe (half-life 2.6 million years) and 55 Fe (half-life 2.7 years).
Iron's most common isotope has a mass number of 56, while the stable isotopes of iron vary in mass number from 54 to 58. Monoisotopic mass is typically expressed in daltons (Da), also called unified atomic mass units (u).
The molar mass of atoms of an element is given by the relative atomic mass of the element multiplied by the molar mass constant, M u ≈ 1.000 000 × 10 −3 kg/mol ≈ 1 g/mol. For normal samples from Earth with typical isotope composition, the atomic weight can be approximated by the standard atomic weight [ 2 ] or the conventional atomic weight.
(near r.t.) 7.3 g/cm 3: 26 Fe iron; use: 7.86 g/cm 3: WEL (near r.t.) 7874 kg/m 3: LNG ... 5.94 g/cm 3: 58 Ce cerium; use: 6.55 g/cm 3: CR2 (at m.p.) 6.55 g/cm 3: 59 ...
Iron is a chemical element; it has the symbol Fe (from Latin ferrum 'iron') and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's outer and inner core.
For other isotopes, the isotopic mass is usually within 0.1 u of the mass number. For example, 35 Cl (17 protons and 18 neutrons) has a mass number of 35 and an isotopic mass of 34.96885. [7] The difference of the actual isotopic mass minus the mass number of an atom is known as the mass excess, [8] which for 35 Cl is –0.03115.
The nominal mass is not always the lowest mass number, for example iron has isotopes 54 Fe, 56 Fe, 57 Fe, and 58 Fe with abundances 6%, 92%, 2%, and 0.3%, respectively, and a nominal mass of 56 Da.
Isotopes of lithium, beryllium, and boron are less strongly bound than helium, as shown by their increasing mass-to-mass number ratios. At carbon, the ratio of mass (in daltons) to mass number is defined as 1, and after carbon it becomes less than one until a minimum is reached at iron-56 (with only slightly higher values for iron-58 and nickel ...