Electron Shell

What are Shells?

According to Bohr’s Atomic model electrons revolve around the nucleus in a specific circular path known as orbit or called a shell. Shells have stationary energy levels, the energy of each shell is constant.

Each stationary orbit or shell is associated with a definite amount of energy. The greater the distance of the orbit from the nucleus, the more shall be the energy associated with it. These shells are called energy levels. It is numbered as 1, 2, 3, 4, ……. or K, L, M, N, ….. from the nucleus outwards.

An electron shell may contain only a fixed number of electrons, each shell is associated with a particular range of electron energy, and thus each shell must fill completely before electrons can be added to an outer shell.

Table of Contents

Characteristic of Shells

  • The principal quantum number is denoted by ‘n’. It represents the name, size and energy of the shell to which the electron belongs. The value of n lies between 1 to ∞.

The value of ‘n’ Designation of shell
1 K
2 L
3 M
4 N
5 O
6 P
7 Q
  • Higher the value of ‘n’ the greater the distance of the shell from the nucleus.

r1 < r2 < r3 < r4 <…….

r = (n2/Z) x 0.529 Å

  • Greater the value of ‘n’ higher the magnitude of energy.

E1 < E2 < E3 < E4 < E5

  • Energy separation between two shells decreases on moving away from the nucleus.

(E2 – E1) > (E3 – E2) > (E4 – E3) > ……..

  • The maximum number of electrons present in the shell on the 2n2 rule.
Name of Shell The value of ‘n’ Maximum electrons present (2n2)
K 1 2
L 2 8
M 3 18
N 4 32
  • The angular momentum of each shell can be calculated by the formula.

mvr = (nh/2π)

Definition of Subshell

All the electrons having the same shall do not have the same energy. Based on the energy of the electrons, the shells are divided into sublevels or subshells. Each shell is composed of one or more subshells, which are themselves composed of atomic orbitals.

  • The subshells are described with the help of Azimuthal quantum numbers (l).
  • The value of l’ depends upon the value of the shell (n) with which it is associated.
  • These subshells have been designated as s (l = 0), p (l =1), d (l = 2) and f (l =3) .
  • The energies of the various subshells in the same shell are in the order s < p < d <f.
  • The subshell having equal l’ value but with different n values have similar shape but their size increases as the value of n increases. 2s- subshell is greater in size than 1s- subshell.
  • The maximum electrons present in a subshell = 2(2l +1).
Subshell Maximum electrons The historical name of subshell
s 2 sharp
p 6 principal
d 10 diffuse
f 14 fundamental

Number of electrons present in the shell

  • Each shell contains one or more subshells.
  • K shell contains only one subshell – 1s
  • L shell contains two subshells – 2s, 2p
  • M shell contains three subshells – 3s, 3p, 3d
  • N shell contains four subshells – 4s, 4p, 4d, 4f

The electrons are arranged in the shell in the following manner:

Name of the shell Name of the subshell Maximum no. of electrons present in the shell Distribute the electron in the subshell
K 1s 2 1s2
L 2s, 2p 8 2s2 2p6
M 3s, 3p, 3d 18 3s2, 3p6, 3d10
N 4s, 4p, 4d, 4f 32 4s2, 4p6, 4d10, 4f14

The order of energy of the subshell

The filling of the shells and subshells with electrons proceeds from subshells of lower energy to subshells of higher energy. This follows the Aufbau principle.

According to this subshells with a lower n + ℓ value are filled before those with higher n + ℓ values. In the case of equal n + ℓ values, the subshell with a lower n value is filled first.

A subshell that has a lower n + ℓ means lower energy. Among 4s and 3d;

4s ; (n + l) = (4 + 0) = 4

3d ; (n + l) = (3 + 2) = 5

4s < 3d (energy)

The energy order of the subshells is given below

Arrangement of electrons in the shell and subshell

The first 20 element electrons are arranged in shell and subshell according to their energy level in the below table.

Atomic Number Element Name K L M
1 Hydrogen (H) 1s1
2 Helium (He) 1s2
3 Lithium (Li) 1s2 2s1
4 Beryllium (Be) 1s2 2s2
5 Boron (B) 1s2 2s2 2p1
6 Carbon (C) 1s2 2s2 2p2
7 Nitrogen (N) 1s2 2s2 2p3
8 Oxygen (O) 1s2 2s2 2p4
9 Fluorine (F) 1s2 2s2 2p5
10 Neon (Ne) 1s2 2s2 2p6
11 Sodium (Na) 1s2 2s2 2p6 3s1
12 Magnesium (Mg) 1s2 2s2 2p6 3s2
13 Aluminium (Al) 1s2 2s2 2p6 3s2 3p1
14 Silicon (Si) 1s2 2s2 2p6 3s2 3p2
15 Phosphorous (P) 1s2 2s2 2p6 3s2 3p3
16 Sulfur (S) 1s2 2s2 2p6 3s2 3p4
17 Chlorine (Cl) 1s2 2s2 2p6 3s2 3p5
18 Argon (Ar) 1s2 2s2 2p6 3s2 3p6
19 Potassium (K) 1s2 2s2 2p6 3s2 3p6 4s1
20 Calcium (Ca) 1s2 2s2 2p6 3s2 3p6 4s2

In order to know more about the electronic configuration of an element, you may visit our website.

Electronic configuration.

Frequently Asked Questions on shells

Q1

What are energy shells in chemistry?

The energy shell is associated with a definite amount of energy. The greater the distance of the orbit from the nucleus, the more shall be the energy associated with it. These shells are called energy level

Q2

What are KLM and N shells in chemistry?

The K shell is the first shell or first energy level, L is the second shell and 2nd energy level, and M is the third shell and 3rd energy level. N is the fourth shell and 4th energy level.

Q3

How do electrons fill the shell?

The filling of the electrons in the shells proceeds from the lower energy to higher energy. According to this subshells with a lower n + ℓ value are filled before those with higher n + ℓ values. In the case of equal n + ℓ values, the subshell with a lower n value is filled first.

Q4

How many electrons does chlorine have?

There are 17 electrons present in a chlorine atom.

Q5

What is a valence shell with an example?

The outermost orbital shell of an atom is called its valence shell. These electrons take part in bonding with other atoms. Example sodium (Na) , the electronic configuration of sodium is 1s2 2s2 2p6 3s1 . The valence shell of Na is the M (3rd) shell.

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