Structure

In chemistry and atomic physics, the electron shell can be thought of as an orbital of electrons around the nucleus. The shell closest  to the nucleus is called the “1 shell” (also called the “K shell”), then the “2 shell” (or “L shell”), then the “3 shell” (or “M-shell”), etc., further away from the nucleus. The shell corresponds to the principal quantum number (n = 1, 2, 3, 4 …) or is labelled alphabetically with the letters  in X-ray notation (K, L, M, …).

Each shell can only contain a specified quantity of electrons. The first shell can hold up to 2 electrons, the second shell can hold up to 8 (2 + 6) electrons, and the third shell can hold up to 18 (2 + 6 + 10) electrons and so on. The general formula is that the nth shell can  hold up to 2 (n²) electrons in principle.

Each and every shell consists of one or more subshells, and each subshell consists of one or more atomic orbitals. 

History of electronic shell:

The 1913 Bohr model of an atom sought to place an electron in a continuous orbit, at which time Bohr expanded the internal orbit of the atom to eight electrons as the atom grew larger. In 1913, Bohr built a model of electrons in the element. The presence of electron shells was first experimentally observed  in Charles Barkla’s and Henry Moseley’s X-ray absorption studies. 

However, the final form of the electron shell model  for the number of shell electrons used today was discovered in 1923 by Edmund Stoner, who introduced the principle that the nth shell is described by 2 (N²). Rice field. 

Subshell:

Each shell is made up of one or more subshells, and the subshells are made up of atomic orbitals. For example, the first (K) shell has a subshell named 1s. The second (L) shell has two subshells called 2s and 2p. The third shell has 3s, 3p and 3d. The 4th shell contains 4s, 4p, 4d, 4f. The fifth shell has 5s, 5p, 5d, and 5f, which can theoretically accommodate more  5g subshells that are not occupied by the ground-state electron configurations of  known elements. 

Number of electrons in each shell:

Each subshell is constrained to hold up to 4ℓ + 2 electrons. That is, it looks like this:

1. Each s subshell holds up to 2 electrons.
2. Each p subshell contains up to 6 eelectron.
3. Each d subshell contains up to 10 electrons.
4. Each f subshell contains up to 14 electrons.
5. Each g subshell contains up to 18 electrons.

Therefore, a K-shell containing only  s subshells can hold up to 2 electrons. An L shell containing s and p can hold up to 2 + 6 = 8 electrons. In general, the nth shell can hold up to 2n² electrons.

Energies of subshell and filling order:

It is sometimes claimed that all the electrons in the shell have the same energy, but this is an approximation. However, the electrons in the subshell  have exactly the same energy level, and the later subshell has more energy per electron than the previous subshell. This effect is large enough that the range of energy  associated with shells can overlap.

The filling of electrons into the shell and subshell proceeds from the low energy subshell to the high energy subshell. It follows the n + ℓ rule, also commonly known as Maderung’s rule. Subshells with low n + ℓ values ​​are padded before subshells with high n + ℓ values. With the same n + ℓ values, the subshell is initially filled with the lower n values. 

Valence electrons:

The valence shell is the outermost shell of an unbonded atom and is most likely involved in the nature of all reactions involving the atom and in bonding interactions  with other atoms. Valence electrons are electrons that are associated with an atom and  can participate in the formation of  chemical bonds. In a single covalent bond, both atoms in the bond contribute to valence electrons to form a covalent pair. The presence of valence electrons can determine the chemistry of an element and whether it can bind to other elements. 

Conclusion:

When atoms come into contact with each other, the first interaction is the outermost electron of those atoms, the valence electron. Atoms are the least stable (and therefore the most reactive) if their valence shell is not full. Valence electrons play a major role in the chemical behaviour of elements. 

Electron configurations  help predict how a particular element reacts and what compounds or molecules  different elements  form. These principles  understand the behaviour of all chemicals, from the most basic elements such as hydrogen and helium to the most complex proteins found in the human body.