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electron configuration
in neutral atoms (in the ground state)

Values with a green background are counts that totally fill the subshell. The names of the noble gases have a blue background. The configurations for the elements more massive than rutherfordium have not yet been confirmed experimentally.

Please scroll the list of elements.

sources

NIST. PML.
Atomic Reference Data for Electronic Structure Calculations, Electronic Configurations of the Elements.
Online , retrieved 21 Nov 2019.

A. Kramida, Yu. Ralchenko, J. Reader and the NIST ASD Team (2019).
NIST Atomic Spectra Database (ver. 5.7.1, [Online]
Gaithersburg, MD: National Institute of Standards and Technology.
doi: https://doi.org/10.18434/T4W30F

An authoritative definition of configuration can be found in the IUPAC “Gold Book”:

IUPAC.
A. D. McNaught and A. Wilkinson, compilers.
Compendium of Chemical Terminology. 2nd ed.
Oxford: Blackwell Scientific Publications, 1997.
doi: https://doi.org//10.1351/goldbook

How many electrons can a shell hold?

The shell labels “K”, “L”, “M”, etc. were first used to name electron shells in 1911, back in the days when physicists thought the electrons really were arranged in shells. Though the letters have hung on, more important are the numbers, “K” being 1, “L” 2, and so on. These are the principal quantum numbers, symbol, n, one of the four quantum numbers that describe an electron in an atom. The number of electrons a shell can hold is 2 times the square of the shell's principal quantum number. So, for example, the principal quantum number of the M shell is 3. Three squared is nine, and nine times 2 is 18. The M shell can hold 18 electrons.

How many electrons can a subshell hold?

The subshell labels “s”, “p”, “d”, and “f” are left over from early studies of atomic structure, which were based on lines in the spectra of light emitted by atoms. Lines were described as “sharp” , “principal” , “diffuse” , “fundamental” (some say “fine”). Now the list is extended in alphabetical order after “f” (“g”, “h”, “i”, “k”, and so on; “j” is omitted).

Each letter represents a whole number, beginning with “s” representing zero. This number is the azimuthal quantum number, symbol ℓ, another one of the four quantum numbers of each electron. (By the Pauli exclusion principle, no atom can have two electrons with identical quantum numbers.) The maximum number of electrons the subshell can hold is given by 2(2ℓ + 1). For example:

Notation

The electron configuration for an atom can be written as the principal quantum number, followed by the subshell label with the number of electrons as a superscript. For example, for meitnerium:
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 6d⁷ 7s²

The order in the series can vary, depending on the writer's purpose. Often the interest is the order in which the subshells are filled or emptied as the atom gains or loses electrons, so that is the order of the list. Here, however, we are just concerned with neutral, unexcited atoms, so the sequence is sorted by the principal quantum number.

A much more compact way of writing the configuration is usually used. It is based on the fact that in a noble gas, all the shells that have any electrons in them are full. More massive atoms are built on that foundation, adding electrons in other subshells, until all those subshells are filled to make another noble gas.

Silver atoms are a bit more massive than atoms of the noble gas krypton. Their configurations are:

If we take the parts of the two configurations that are identical (which is the entire configuration for krypton), and substitute the symbol for krypton for that part of the silver configuration, we get the nicely concise:

silver: [Kr] 4d¹⁰ 5s¹

info trek

1. What are orbitals? The web has many sites showing the shapes of the orbitals. A good one is the orbitron by Mark Winter.

2. Can you find the 2-6-10-14 pattern reflected in the periodic table?

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Last revised: 8 November 2021.