is called layered electronic distribution the distribution that takes into account only the amount of electrons maximum in each of the layers (according to the Bohr's atom) of an atom.
The layers that an atom can have are K, L, M, N, O, P and Q. See the maximum amount of electrons in each of them:
K = 2 electrons
L = 8 electrons
M = 18 electrons
N = 32 electrons
O = 32 electrons
P = 18 electrons
Q = 8 electrons
To perform a electronic distribution in layers, it is necessary:
Meet the atomic number of the atom that will be worked, since this number indicates the number of electrons;
Respect the electron limit of each shell, as described above.
Carefully follow each of the rules proposed below:
→ Rule 1: If the number of electrons is enough, the first (K-shell) and second (K-shell) shell of the atom must always receive the maximum number of electrons, which are 2 and 8, respectively;
→ Rule 2: The penultimate shell receiving electrons can never exceed the 18-electron limit;
→ Rule 3: The last shell to receive electrons can never exceed the eight-electron limit;
→ Rule 4: When there are more electrons than can fit in the last shell, we must always repeat the number of electrons from the previous shell and place the remaining electrons in the next shell.
See some examples of layered electronic distribution:
Example 1: Layered distribution of the element sodium, whose atomic number is 11.
Since the atomic number of sodium is 11, its atoms have 11 electrons. Its distribution will be carried out as follows:
Layer K: 2 electrons
Of the eleven electrons, the K shell will receive only two, as this is its electron limit. (rule 1).
Layer L: 8 electrons
Of the remaining nine electrons, the L shell will receive only eight, as this is its electron limit. (rule 2).
Layer M: 1 electron
Since there is only one electron left of the eleven that the sodium atom had, it must be placed in the M shell, which is the next one after the L shell.
Example 2: Layered distribution of the element calcium, whose atomic number is 20.
Since the atomic number of calcium is 20, its atoms have 20 electrons. Its distribution in layers will be carried out as follows:
Layer K: 2 electrons
Of the 20 electrons, the K shell will receive only 2 electrons, as this is its electron limit. (rule 1).
Layer L: 8 electrons
Of the remaining 18 electrons, the L shell will receive only 8, as this is its electron limit. (rule 2).
Layer M: 8 electrons
10 electrons remain after filling the K and L shells. Since the last shell cannot have more than eight electrons, we must repeat the number of electrons from the previous shell (L shell) and place the rest in the next shell (N shell) (rule 4).
Layer N: 2 electrons
Receives the remaining electrons, as they could not be placed in the previous layer (rule 4).
Example 3: Layered distribution of the element bromine, whose atomic number 35.
Since the atomic number of bromine is 35, its atoms have 35 electrons. Its distribution will be carried out as follows:
Layer K: 2 electrons
Of the 35 electrons, the K shell will receive only 2 electrons, as this is its electron limit.
Layer L: 8 electrons
Of the 33 remaining electrons, the L shell will receive only 8 electrons, as this is its electron limit.
Layer M: 18 electrons
As there are 25 electrons left, this shell can only receive 18 electrons, as it will not be the last one, as the last one can only receive 8, but the second to last one can receive 18. Thus, layer M will be the penultimate layer (rule 3).
Layer N: 7 electrons
Of the 35 electrons that the atom had, only seven remain. Since the last shell can receive up to eight electrons, this will be the last shell and will receive the seven electrons.
By Me. Diogo Lopes Dias
Source: Brazil School - https://brasilescola.uol.com.br/quimica/distribuicao-eletronica-camadas.htm