electron configuration
in neutral atoms in the ground state

hydrogen H 1 1                                      
helium He 2 2                                      
lithium Li 3 2 1                                    
beryllium Be 4 2 2                                    
boron B 5 2 2 1                                  
carbon C 6 2 2 2                                  
nitrogen N 7 2 2 3                                  
oxygen O 8 2 2 4                                  
fluorine F 9 2 2 5                                  
neon Ne 10 2 2 6                                  
sodium Na 11 2 2 6 1                                
magnesium Mg 12 2 2 6 2                                
aluminum Al 13 2 2 6 2 1                              
silicon Si 14 2 2 6 2 2                              
phosphorus P 15 2 2 6 2 3                              
sulfur S 16 2 2 6 2 4                              
chlorine Cl 17 2 2 6 2 5                              
argon Ar 18 2 2 6 2 6                              
potassium K 19 2 2 6 2 6   1                          
calcium Ca 20 2 2 6 2 6   2                          
scandium Sc 21 2 2 6 2 6 1 2                          
titanium Ti 22 2 2 6 2 6 2 2                          
vanadium V 23 2 2 6 2 6 3 2                          
chromium Cr 24 2 2 6 2 6 5 1                          
manganese Mn 25 2 2 6 2 6 5 2                          
iron Fe 26 2 2 6 2 6 6 2                          
cobalt Co 27 2 2 6 2 6 7 2                          
nickel Ni 28 2 2 6 2 6 8 2                          
copper Cu 29 2 2 6 2 6 10 1                          
zinc Zn 30 2 2 6 2 6 10 2                          
gallium Ga 31 2 2 6 2 6 10 2 1                        
german­ium Ge 32 2 2 6 2 6 10 2 2                        
arsenic As 33 2 2 6 2 6 10 2 3                        
selenium Se 34 2 2 6 2 6 10 2 4                        
bromine Br 35 2 2 6 2 6 10 2 5                        
krypton Kr 36 2 2 6 2 6 10 2 6                        
rubidium Rb 37 2 2 6 2 6 10 2 6     1                  
strontium St 38 2 2 6 2 6 10 2 6     2                  
yttrium Y 39 2 2 6 2 6 10 2 6 1   2                  
zircon­ium Zr 40 2 2 6 2 6 10 2 6 2   2                  
niobium Nb 41 2 2 6 2 6 10 2 6 4   1                  
molybden­um Mo 42 2 2 6 2 6 10 2 6 5   1                  
techne­tium Tc 43 2 2 6 2 6 10 2 6 5   2                  
ruthenium Ru 44 2 2 6 2 6 10 2 6 7   1                  
rhodium Rh 45 2 2 6 2 6 10 2 6 8   1                  
pallad­ium Pd 46 2 2 6 2 6 10 2 6 10                      
silver Ag 47 2 2 6 2 6 10 2 6 10   1                  
cadmium Cd 48 2 2 6 2 6 10 2 6 10   2                  
indium In 49 2 2 6 2 6 10 2 6 10   2 1                
tin Sn 50 2 2 6 2 6 10 2 6 10   2 2                
antimony Sb 51 2 2 6 2 6 10 2 6 10   2 3                
tellurium Te 52 2 2 6 2 6 10 2 6 10   2 4                
iodine I 53 2 2 6 2 6 10 2 6 10   2 5                
xenon Xe 54 2 2 6 2 6 10 2 6 10   2 6                
cesium Cs 55 2 2 6 2 6 10 2 6 10   2 6     1          
barium Ba 56 2 2 6 2 6 10 2 6 10   2 6     2          
lanthanum La 57 2 2 6 2 6 10 2 6 10   2 6 1   2          
cerium Ce 58 2 2 6 2 6 10 2 6 10 1 2 6 1   2          
praseo­dymium Pr 59 2 2 6 2 6 10 2 6 10 3 2 6     2          
neodymium Nd 60 2 2 6 2 6 10 2 6 10 4 2 6     2          
prometh­ium Pm 61 2 2 6 2 6 10 2 6 10 5 2 6     2          
samarium Sm 62 2 2 6 2 6 10 2 6 10 6 2 6     2          
europ­ium Eu 63 2 2 6 2 6 10 2 6 10 7 2 6     2          
gadolin­ium Gd 64 2 2 6 2 6 10 2 6 10 7 2 6 1   2          
terbium Tb 65 2 2 6 2 6 10 2 6 10 9 2 6     2          
dyspros­ium Dy 66 2 2 6 2 6 10 2 6 10 10 2 6     2          
holmium Ho 67 2 2 6 2 6 10 2 6 10 11 2 6     2          
erbium Er 68 2 2 6 2 6 10 2 6 10 12 2 6     2          
thulium Tm 69 2 2 6 2 6 10 2 6 10 13 2 6     2          
ytterbium Yb 70 2 2 6 2 6 10 2 6 10 14 2 6     2          
lutetium Lu 71 2 2 6 2 6 10 2 6 10 14 2 6 1   2          
hafnium Hf 72 2 2 6 2 6 10 2 6 10 14 2 6 2   2          
tantalum Ta 73 2 2 6 2 6 10 2 6 10 14 2 6 3   2          
tungsten W 74 2 2 6 2 6 10 2 6 10 14 2 6 4   2          
rhenium Re 75 2 2 6 2 6 10 2 6 10 14 2 6 5   2          
osmium Os 76 2 2 6 2 6 10 2 6 10 14 2 6 6   2          
iridium Ir 77 2 2 6 2 6 10 2 6 10 14 2 6 7   2          
platinum Pt 78 2 2 6 2 6 10 2 6 10 14 2 6 9   1          
gold Au 79 2 2 6 2 6 10 2 6 10 14 2 6 10   1          
mercury Hg 80 2 2 6 2 6 10 2 6 10 14 2 6 10   2          
thallium Tl 81 2 2 6 2 6 10 2 6 10 14 2 6 10   2 1        
lead Pb 82 2 2 6 2 6 10 2 6 10 14 2 6 10   2 2        
bismuth Bi 83 2 2 6 2 6 10 2 6 10 14 2 6 10   2 3        
polonium Po 84 2 2 6 2 6 10 2 6 10 14 2 6 10   2 4        
astatine At 85 2 2 6 2 6 10 2 6 10 14 2 6 10   2 5        
radon Rn 86 2 2 6 2 6 10 2 6 10 14 2 6 10   2 6        
francium Fr 87 2 2 6 2 6 10 2 6 10 14 2 6 10   2 6     1  
radium Ra 88 2 2 6 2 6 10 2 6 10 14 2 6 10   2 6     2  
actinium Ac 89 2 2 6 2 6 10 2 6 10 14 2 6 10   2 6 1   2  
thorium Th 90 2 2 6 2 6 10 2 6 10 14 2 6 10   2 6 2   2  
protact­inium Pa 91 2 2 6 2 6 10 2 6 10 14 2 6 10 2 2 6 1   2  
uranium U 92 2 2 6 2 6 10 2 6 10 14 2 6 10 3 2 6 1   2  
neptunium Np 93 2 2 6 2 6 10 2 6 10 14 2 6 10 4 2 7 1   2  
plutonium Pu 94 2 2 6 2 6 10 2 6 10 14 2 6 10 6 2 6     2  
americium Am 95 2 2 6 2 6 10 2 6 10 14 2 6 10 7 2 6     2  
curium Cm 96 2 2 6 2 6 10 2 6 10 14 2 6 10 7 2 6 1   2  
berkel­ium Bk 97 2 2 6 2 6 10 2 6 10 14 2 6 10 9 2 6     2  
californ­ium Cf 98 2 2 6 2 6 10 2 6 10 14 2 6 10 10 2 6     2  
einstein­ium Es 99 2 2 6 2 6 10 2 6 10 14 2 6 10 11 2 6     2  
fermium Fm 100 2 2 6 2 6 10 2 6 10 14 2 6 10 12 2 6     2  
mendelev­ium Md 101 2 2 6 2 6 10 2 6 10 14 2 6 10 13 2 6     2  
nobelium No 102 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6     2  
lawrenc­ium Lr 103 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6     2 1
ruther­fordium Rf 104 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 2   2  
dubnium Db 105 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 3   2  
seaborg­ium Sg 106 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 4   2  
bohrium Bh 107 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 5   2  
hassium Hs 108 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 6   2  
meitner­ium Mt 109 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 7   2  
darmstadt­ium Ds 110 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 9   1  
roentgen­ium Rg 111 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 10   1  
copernicium Cn 112 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 10   2  
nihonium Nh 113 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 10   2 1
flerov­ium Fl 114 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 10   2 2
moscov­ium Mc 115 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 10   2 3
livermor­ium Lv 116 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 10   2 4
tenness­ine Ts 117 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 10   2 5
oganesson Og 118 2 2 6 2 6 10 2 6 10 14 2 6 10 14 2 6 10 14 2 6
                                             

The blue rows mark the noble gases. The configurations for the elements more massive than rutherfordium are not yet confirmed experimentally.

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

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:

  2(2ℓ + 1) maximum number of electrons
the subshell can hold
s 0 2(0 +1) 2
p 1 2(2 + 1) 6
d 2 2(4 +1) 10
f 3 2(6 + 1) 14
g 4 and so on...

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.

Meitnerium atoms are a bit more massive than atoms of the noble gas radon. Their configurations are:

radon:         1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶  5d¹⁰        6s² 6p⁶ 

meitnerium: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶  5d¹⁰ 5f¹⁴ 6s² 6p⁶  6d⁷ 7s²

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

meitnerium: [Rn] 5f¹⁴ 6d⁷ 7s²

info trek

1. What are orbitals? The web has many sites showing the shapes of the orbitals. A good one was the orbitron by Mark Winter. Unfortunately, Professor Winter created it using Flash, which is insecure and is now deprecated. If, however, your system is running flash, the site is worth a look.

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

Long form of the periodic table

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