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Electron Configurations Of Elements

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Updated 2009-03-12 00:15

Filling of Electronic Subshells in Elements

Mnemonic:
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
7s 7p
The subshells fill diagonally from upper right to lower left in the chart above:
First is 1s, then 2s, then 2p and 3s, then 3p and 4s.
Next comes 3d, 4p, and 5s. Then comes 4d, 5p, and 6s.
After that comes 4f, 5d, 6p, and 7s. Last comes 5f, 6d, and 7p.

 

For an atom with 118 electrons, the electron orbital configuration would be:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6
The electron orbital configurations for atoms with less electrons will be truncated versions of this 118-electron configuration.

 

There are many exceptions to this order among the d- and f- Transition Elements
since (n+2)s, (n+1)d, and (n)f orbitals are close in energy when n is large.

 

The total of the superscripts in an element's electron configuration equals
the total number of electrons in an atom of that element.

 

Long electron configurations can be abbreviated by finding the right-most p6 and
replacing this and all electrons to the left with the equivalent noble gas listed in []:
1s2 becomes [He],
1s2 2s2 2p6 becomes [Ne],
1s2 2s2 2p6 3s2 3p6 becomes [Ar],
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 becomes [Kr],
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 becomes [Xe], and
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 becomes [Rn].
Thus, P (1s2 2s2 2p6 3s2 3p3) becomes [Ne] 3s2 3p3.

 

See Electronic Orbital Properties for more details.

Electron Configurations of Elements

ElementElectron Configuration
H Hydrogen1s1
C Carbon1s2 2s2 2p2 = [He] 2s2 2p2
N Nitrogen1s2 2s2 2p3 = [He] 2s2 2p3
O Oxygen1s2 2s2 2p4 = [He] 2s2 2p4
Na Sodium1s2 2s2 2p6 3s1 = [Ne] 3s1
Mg Magnesium1s2 2s2 2p6 3s2 = [Ne] 3s2
P Phosphorus[Ne] 3s2 3p3
S Sulfur[Ne] 3s2 3p4
Cl Chlorine[Ne] 3s2 3p5
K Potassium[Ar] 4s1
Ca Calcium[Ar] 4s2
memorize

 

ElementElectron Configuration
V Vanadium[Ar] 4s2 3d3
Cr Chromium[Ar] 4s1 3d5 ***
Mn Manganese[Ar] 4s2 3d5
Fe Iron[Ar] 4s2 3d6
Co Cobalt[Ar] 4s2 3d7
Ni Nickel[Ar] 4s2 3d8
Cu Copper[Ar] 4s1 3d10 ***
Zn Zinc[Ar] 4s2 3d10
Se Selenium[Ar] 4s2 3d10 4p4
Mo Molybdenum[Kr] 5s1 4d5 ***
I Iodine[Kr] 5s2 4d10 5p5
W Tungsten[Xe] 6s2 4f14 5d4
memorize

 

*** above does not fill 4s before 3d, or does not fill 5s before 4d

 

ElementElectron Configuration
He Helium1s2
Li Lithium1s2 2s1 = [He] 2s1
Be Beryllium1s2 2s2 = [He] 2s2
B Boron1s2 2s2 2p1 = [He] 2s2 2p1
F Fluorine1s2 2s2 2p5 = [He] 2s2 2p5
Ne Neon1s2 2s2 2p6 = [He] 2s2 2p6
Al Aluminum[Ne] 3s2 3p1
Si Silicon[Ne] 3s2 3p2
Ar Argon[Ne] 3s2 3p6
memorize

 

ElementElectron Configuration
Sc Scandium[Ar] 4s2 3d1
Ti Titanium[Ar] 4s2 3d2
Ga Gallium[Ar] 4s2 3d10 4p1
Ge Germanium[Ar] 4s2 3d10 4p2
As Arsenic[Ar] 4s2 3d10 4p3
Br Bromine[Ar] 4s2 3d10 4p5
Kr Krypton[Ar] 4s2 3d10 4p6
Ag Silver[Kr] 5s1 4d10 ***
Cd Cadmium[Kr] 5s2 4d10
Sn Tin[Kr] 5s2 4d10 5p2
Sb Antimony[Kr] 5s2 4d10 5p3
Xe Xenon[Kr] 5s2 4d10 5p6
memorize

 

*** above does not fill 5s before 4d

 

ElementElectron Configuration
Gd Gadolinium[Xe] 6s2 4f7 5d1
Pt Platinum[Xe] 6s1 4f14 5d9 ***
Au Gold[Xe] 6s1 4f14 5d10 ***
Hg Mercury[Xe] 6s2 4f14 5d10
Pb Lead[Xe] 6s2 4f14 5d10 6p2
Bi Bismuth[Xe] 6s2 4f14 5d10 6p3
Rn Radon[Xe] 6s2 4f14 5d10 6p6
U Uranium[Rn] 7s2 5f3 6d1 ***
memorize

 

*** above does not fill 6s before 5d, or does not fill 5f before 6d

Exceptions to General Orbital-Filling Order Rules

ElementElectron Configuration
Cr Chromium[Ar] 4s1 3d5 ***
Cu Copper[Ar] 4s1 3d10 ***
Nb Niobium[Kr] 5s1 4d4 ***
Mo Molybdenum[Kr] 5s1 4d5 ***
Tc Technetium[Kr] 5s1 4d6 ***
Ru Ruthenium[Kr] 5s1 4d7 ***
Rh Rhodium[Kr] 5s1 4d8 ***
Pd Palladium[Kr] 5s0 4d10 ***
Ag Silver[Kr] 5s1 4d10 ***
Ce Cerium[Xe] 6s2 4f1 5d1 ***
Gd Gadolinium[Xe] 6s2 4f7 5d1 ***
Pt Platinum[Xe] 6s1 4f14 5d9 ***
Au Gold[Xe] 6s1 4f14 5d10 ***
Th Thorium[Rn] 7s2 5f0 6d2 ***
Pa Protactinium[Rn] 7s2 5f2 6d1 ***
U Uranium[Rn] 7s2 5f3 6d1 ***
Np Neptunium[Rn] 7s2 5f4 6d1 ***
Cm Curium[Rn] 7s2 5f7 6d1 ***
memorize

 

*** above does not fill 4s before 3d, 5s before 4d, 6s before 4f before 5d,
       or 7s before 5f before 6d

References:

 

http://wwww.dayah.com/periodic/

 

p.268 of "Chemistry" by Steven S. Zumdahl, 1986,
D. C. Heath and Company (ISBN=0-669-04529-2).