Core electrons are the electrons in an atom that are not valence electrons and do not participate in chemical bonding.[1] The nucleus and the core electrons of an atom form the atomic core. Core electrons are tightly bound to the nucleus. Therefore, unlike valence electrons, core electrons play a secondary role in chemical bonding and reactions by screening the positive charge of the atomic nucleus from the valence electrons.[2]
The number of valence electrons of an element can be determined by the periodic table group of the element (see valence electron):
- For main group elements, the number of valence electrons ranges from 1-8 electrons (ns and np orbitals).
- For transition metals, the number of valence electrons ranges from 3-12 electrons (ns and (n−1)d orbitals).
- For lanthanides and actinides, the number of valence electrons ranges from 3-16 electrons (ns, (n−2)f and (n−1)d orbitals).
All other non-valence electrons for an atom of that element are considered core electrons.
https://en.wikipedia.org/wiki/Characteristic_X-ray
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