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  2. Mass number - Wikipedia

    en.wikipedia.org/wiki/Mass_number

    The mass number is different for each isotope of a given chemical element, and the difference between the mass number and the atomic number Z gives the number of neutrons (N) in the nucleus: N = A − Z. [2] The mass number is written either after the element name or as a superscript to the left of an element's symbol.

  3. Atomic mass - Wikipedia

    en.wikipedia.org/wiki/Atomic_mass

    Binding energy per nucleon of common isotopes. A graph of the ratio of mass number to atomic mass would be similar. The amount that the ratio of atomic masses to mass number deviates from 1 is as follows: the deviation starts positive at hydrogen-1, then decreases until it reaches a local minimum at helium-4. Isotopes of lithium, beryllium, and ...

  4. 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.

  5. Atom - Wikipedia

    en.wikipedia.org/wiki/Atom

    This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit, each carbon-12 atom has an atomic mass of exactly 12 Da, and so a mole of carbon-12 atoms weighs exactly 0.012 kg. [65]

  6. Periodic table - Wikipedia

    en.wikipedia.org/wiki/Periodic_table

    When atomic mass is shown, it is usually the weighted average of naturally occurring isotopes; but if no isotopes occur naturally in significant quantities, the mass of the most stable isotope usually appears, often in parentheses. [8] In the standard periodic table, the elements are listed in order of increasing atomic number.

  7. Whole number rule - Wikipedia

    en.wikipedia.org/wiki/Whole_number_rule

    In chemistry, the whole number rule states that the masses of the isotopes are whole number multiples of the mass of the hydrogen atom. [1] The rule is a modified version of Prout's hypothesis proposed in 1815, to the effect that atomic weights are multiples of the weight of the hydrogen atom. [ 2 ]

  8. Chemical element - Wikipedia

    en.wikipedia.org/wiki/Chemical_element

    Whereas the mass number simply counts the total number of neutrons and protons and is thus an integer, the atomic mass of a particular isotope (or "nuclide") of the element is the mass of a single atom of that isotope, and is typically expressed in daltons (symbol: Da), or universal atomic mass units (symbol: u).

  9. Chemical symbol - Wikipedia

    en.wikipedia.org/wiki/Chemical_symbol

    The nucleon number (mass number) is shown in the left superscript position (e.g., 14 N). This number defines the specific isotope. Various letters, such as "m" and "f" may also be used here to indicate a nuclear isomer (e.g., 99m Tc). Alternately, the number here can represent a specific spin state (e.g., 1 O 2). These details can be omitted if ...

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