Viewed simply, electrons are arranged in shells around an atom's nucleus. Electrons closest to the nucleus will have the lowest energy. Electrons further away from the nucleus will have higher energy. ... In a more realistic model, electrons move in atomic orbitals, or subshells.
By definition:
The Electronic Configuration of the elements is the arrangement of all electrons of an element in energy levels and sub-levels (orbitals).
There are 7 energy levels, numbered from 1 to 7, and in which electrons are distributed, logically in order according to their energy level. Electrons with less energy will be spinning at level 1.
Each level is divided into sub-levels. These sub-levels into which each level is divided can be up to 4. These 4 sub-levels are called: s, p, d, f.
In the sub-level s there can only be a maximum of 2 electrons, in sub-level p there can be a maximum of 6 electrons, in the sub-level d 10 electrons and finally in the sub-level f there can be a maximum of 14 electrons.
Aufbau's principle is a principle of atomic physics, which explains how electrons are accommodated in their orbits around the nucleus of the atom. This principle states that the filling of these orbitals occurs in increasing order of energy, that is, from the orbitals of lower energy to those of higher energy.
The simplest of the sub-levels is 1s. If you fill the 1s you can start filling the 2s. After the 2s sub-level is satisfied, the 2p can begin to fill and so on. The order is:
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²5f¹⁴6d¹⁰7p⁶
In this way, taking into account the atomic number Z of the element (which represents the number of protons of the element, and in a neutral atom it also indicates the number of electrons), the electrons that it has in the orbitals will be placed following the previously established.
For example, for hydrogen, whose atomic number is Z = 1, its electronic configuration would be: 1s¹.
Remember that the number 1 that precedes the representative letter of the orbital indicates the level of energy where the electron is located, the letter s indicates the type of orbital where the electron is located, and the exponent 1 indicates the number of electrons that are located in said orbital.
In summary:
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