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  2. Mass number - Wikipedia

    en.wikipedia.org/wiki/Mass_number

    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. For example, 35 Cl (17 protons and 18 neutrons) has a mass number of 35 and an isotopic mass of 34.96885. [7]

  3. Island of stability - Wikipedia

    en.wikipedia.org/wiki/Island_of_stability

    Considering all decay modes, various models indicate a shift of the center of the island (i.e., the longest-living nuclide) from 298 Fl to a lower atomic number, and competition between alpha decay and spontaneous fission in these nuclides; [83] these include 100-year half-lives for 291 Cn and 293 Cn, [55] [78] a 1000-year half-life for 296 Cn ...

  4. Atomic mass - Wikipedia

    en.wikipedia.org/wiki/Atomic_mass

    Since free protons and neutrons differ from each other in mass by a small fraction of a dalton (1.388 449 33 (49) × 10 −3 Da), [9] rounding the relative isotopic mass, or the atomic mass of any given nuclide given in daltons to the nearest whole number, always gives the nucleon count, or mass number.

  5. Atomic number - Wikipedia

    en.wikipedia.org/wiki/Atomic_number

    The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary uncharged atom, the atomic number is also equal to the number of electrons. For an ordinary atom which contains protons, neutrons and electrons, the sum of the atomic number Z and the neutron number N gives the atom's atomic mass number A.

  6. Periodic table - Wikipedia

    en.wikipedia.org/wiki/Periodic_table

    Each distinct atomic number therefore corresponds to a class of atom: these classes are called the chemical elements. [5] The chemical elements are what the periodic table classifies and organizes. Hydrogen is the element with atomic number 1; helium, atomic number 2; lithium, atomic number 3; and so on.

  7. List of elements by atomic properties - Wikipedia

    en.wikipedia.org/wiki/List_of_elements_by_atomic...

    This is a list of chemical elements and their atomic properties, ordered by atomic number (Z). Since valence electrons are not clearly defined for the d-block and f-block elements, there not being a clear point at which further ionisation becomes unprofitable, a purely formal definition as number of electrons in the outermost shell has been used.

  8. Effective atomic number (compounds and mixtures) - Wikipedia

    en.wikipedia.org/wiki/Effective_atomic_number...

    is the atomic number of each element. An example is that of water (H 2 O), made up of two hydrogen atoms (Z=1) and one oxygen atom (Z=8), the total number of electrons is 1+1+8 = 10, so the fraction of electrons for the two hydrogens is (2/10) and for the one oxygen is (8/10).

  9. Atomic units - Wikipedia

    en.wikipedia.org/wiki/Atomic_units

    A set of base units in the atomic system as in one proposal are the electron rest mass, the magnitude of the electronic charge, the Planck constant, and the permittivity. [6] [9] In the atomic units system, each of these takes the value 1; the corresponding values in the International System of Units [10]: 132 are given in the table.

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