Shells and Subshells

Aufbau Principle for electronic configuration

Aufbau Principle and filling of electrons in orbitals and sub shells

The Aufbau Principle is a concept used to explain the electronic configuration of atoms. The principle states that electrons occupy the lowest available energy levels in an atom, from lowest to highest energy. While no single scientist is credited with discovering this principle, it has been referenced by many scientists over time and continues to be fundamental in understanding atomic structure. Aufbau Principle for electronic configuration is not on the name of any scientist as usually happened in sciences. Aufbau means building up.

Electrons are build up in orbitals of different subshells of different energy levels on the basis of energy.

Electrons first fill lower energy level and then move to next higher level.

s orbitals
s orbitals

So electrons start filling from 1s orbital on wards in the following sequence:

1s,2s,2p , 3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,7s,5f,6d,7p,8s

Simply it can be learned as ssp sps dps dps fdps fdps

Aufbau principle diagram by hand
Atomic Number Element Electronic Configuration
1 Hydrogen Is1
2 Helium      Is2
3 Lithium 1s2 2s1
4 Beryllium 1s2 2s2
5 Boron      1s2 2s2 2p1
6 Carbon  1s2 2s2 2p2
7 Nitrogen   1s2 2s2 2p3
8 Oxygen   1s2 2s2 2p4
9 Fluorine  1s2 2s2 2p5
10 Neon   1s2 2s2 2p6
11 Sodium 1s22s22p63s1
12 Magnesium 1s22s22p63s2
13 Aluminium 1s22s22p63s23p1
14 Silicon 1s22s22p63s23p2
15 Phosphorus 1s22s22p63s23p3
16 Sulphur 1s22s22p63s23p4
17 Chlorine 1s22s22p63s23p5
18 Argon 1s22s22p63s23p6
19 Potassium 1s22s22p63s23p64s1
20 Calcium 1s22s22p63s23p64s2
21 Scandium  1s22s22p63s23p64s2 3d1
22 Titanium 1s22s22p63s23p64s2 3d2
23 Vanadium 1s22s22p63s23p64s2 3d3
24 Chromium 1s22s22p63s23p64s1 3d5
25 Manganese 1s22s22p63s23p64s2 3d5
26 Iron 1s22s22p63s23p64s2 3d6
27 Cobalt 1s22s22p63s23p64s2 3d7
28 Nickel 1s22s22p63s23p64s2 3d8
29 Copper 1s22s22p63s23p64s1 3d10

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