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  2. Magnesium - Wikipedia

    en.wikipedia.org/wiki/Magnesium

    Magnesium is a chemical element; it has symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. ...

  3. Isotopes of magnesium - Wikipedia

    en.wikipedia.org/wiki/Isotopes_of_magnesium

    Magnesium (12 Mg) naturally occurs in three stable isotopes: 24 Mg, 25 Mg, and 26 Mg. There are 19 radioisotopes that have been discovered, ranging from 18 Mg to 40 Mg (with the exception of 39 Mg). The longest-lived radioisotope is 28 Mg with a half-life of 20.915(9) h.

  4. Chemical element - Wikipedia

    en.wikipedia.org/wiki/Chemical_element

    Thus, magnesium-24 (24 is the mass number) is an atom with 24 nucleons (12 protons and 12 neutrons). 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 ...

  5. List of elements by stability of isotopes - Wikipedia

    en.wikipedia.org/wiki/List_of_elements_by...

    The darker more stable isotope region departs from the line of protons (Z) = neutrons (N), as the element number Z becomes larger. This is a list of chemical elements by the stability of their isotopes. Of the first 82 elements in the periodic table, 80 have isotopes considered to be stable. [1] Overall, there are 251 known stable isotopes in ...

  6. Electron shell - Wikipedia

    en.wikipedia.org/wiki/Electron_shell

    Each shell can contain only a fixed number of ... because the number of electrons in an electrically neutral atom equals the number of protons, ... Magnesium: 2, 8, 2 ...

  7. List of chemical elements - Wikipedia

    en.wikipedia.org/wiki/List_of_chemical_elements

    Like the periodic table, the list below organizes the elements by the number of protons in their atoms; ... see magnesium: 7 4 d-block 54.938: 7.21: 1519: 2334: 0.479 ...

  8. Atomic number - Wikipedia

    en.wikipedia.org/wiki/Atomic_number

    The atomic number or nuclear charge number (symbol Z) of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons , this is equal to the proton number ( n p ) or the number of protons found in the nucleus of every atom of that element.

  9. Periodic table - Wikipedia

    en.wikipedia.org/wiki/Periodic_table

    Each chemical element has a unique atomic number (Z— for "Zahl", German for "number") representing the number of protons in its nucleus. [4] 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.