principal quantum number
Sign in to saveone of four quantum numbers which are assigned to each electron in an atom to describe that electron's state
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Encyclopedic overview
In quantum mechanics, the principal quantum number (n) of an electron in an atom indicates which electron shell or energy level it is in. Its values are natural numbers (1, 2, 3, ...).
Hydrogen and Helium, at their lowest energies, have just one electron shell. Lithium through Neon (see periodic table) have two shells: two electrons in the first shell, and up to 8 in the second shell. Larger atoms have more shells.
Excerpted from Wikipedia’s “principal quantum number” article, available under the CC BY-SA 4.0 licence.