Complete Electron Configuration for Indium (In, In3+)
Indium is the 49th element in the periodic table and its symbol is ‘In’. Indium is a posttransition metal element. In this article, I have discussed in detail how to easily write the complete electron configuration of indium.
What is the electron configuration of indium?
The total number of electrons in indium is fortynine. These electrons are arranged according to specific rules in different orbitals.
The arrangement of electrons in indium in specific rules in different orbits and orbitals is called the electron configuration of indium.
The electron configuration of indium is [Kr] 4d^{10} 5s^{2} 5p^{1}, if the electron arrangement is through orbitals. Electron configuration can be done in two ways.
 Electron configuration through orbit (Bohr principle)
 Electron configuration through orbital (Aufbau principle)
Electron configuration through orbitals follows different principles. For example Aufbau principle, Hund’s principle, and Pauli’s exclusion principle.
Indium atom electron configuration through orbit
Scientist Niels Bohr was the first to give an idea of the atom’s orbit. He provided a model of the atom in 1913. The complete idea of the orbit is given there.
The electrons of the atom revolve around the nucleus in a certain circular path. These circular paths are called orbit(shell). These orbits are expressed by n. [n = 1,2,3,4 . . . The serial number of the orbit]
K is the name of the first orbit, L is the second, M is the third, and N is the name of the fourth orbit. The electron holding capacity of each orbit is 2n^{2}.
Shell Number (n)  Shell Name  Electrons Holding Capacity (2n^{2}) 
1  K  2 
2  L  8 
3  M  18 
4  N  32 
For example,
 n = 1 for K orbit.
The maximum electron holding capacity in K orbit is 2n^{2} = 2 × 1^{2} = 2.  For L orbit, n = 2.
The maximum electron holding capacity in L orbit is 2n^{2} = 2 × 2^{2} = 8.  n=3 for M orbit.
The maximum electron holding capacity in M orbit is 2n^{2} = 2 × 3^{2 }= 18.  n=4 for N orbit.
The maximum electron holding capacity in N orbit is 2n^{2} = 2 × 4^{2} = 32.
Therefore, the maximum electron holding capacity in the first shell is two, the second shell is eight and the 3rd shell can have a maximum of eighteen electrons. The atomic number is the number of electrons in that element.
The atomic number of indium is 49. That is, the number of electrons in indium is fortynine. Therefore, an indium atom will have two electrons in the first shell, eight in the 2nd orbit, and eighteen electrons in the 3rd shell.
According to Bohr’s formula, the fourth shell will have twentyone electrons but the fourth shell of indium will have eighteen electrons and the remaining three electrons will be in the fifth shell.
Therefore, the order of the number of electrons in each shell of the indium atom is 2, 8, 18, 18, 3. Electrons can be arranged correctly through orbits from elements 1 to 18.
The electron configuration of an element with an atomic number greater than 18 cannot be properly determined according to the Bohr atomic model. The electron configuration of all the elements can be done through the orbital diagram.
Electron configuration of indium through orbital
Atomic energy shells are subdivided into subenergy levels. These subenergy levels are also called orbital. The most probable region of electron rotation around the nucleus is called the orbital.
The subenergy levels depend on the azimuthal quantum number. It is expressed by ‘l’. The value of ‘l’ is from 0 to (n – 1). The subenergy levels are known as s, p, d, and f.
Orbit Number  Value of ‘l’  Number of subshells  Number of orbital  Subshell name  Electrons holding capacity  Electron configuration 
1  0  1  1  1s  2  1s^{2} 
2  0 1  2  1 3  2s 2p  2 6  2s^{2} 2p^{6} 
3  0 1 2  3  1 3 5  3s 3p 3d  2 6 10  3s^{2} 3p^{6} 3d^{10} 
4  0 1 2 3  4  1 3 5 7  4s 4p 4d 4f  2 6 10 14  4s^{2} 4p^{6} 4d^{10} 4f^{14} 
For example,
 If n = 1,
(n – 1) = (1–1) = 0
Therefore, the value of ‘l’ is 0. So, the subenergy level is 1s.  If n = 2,
(n – 1) = (2–1) = 1.
Therefore, the value of ‘l’ is 0, 1. So, the subenergy levels are 2s, and 2p.  If n = 3,
(n – 1) = (3–1) = 2.
Therefore, the value of ‘l’ is 0, 1, 2. So, the subenergy levels are 3s, 3p, and 3d.  If n = 4,
(n – 1) = (4–1) = 3
Therefore, the value of ‘l’ is 0, 1, 2, 3. So, the subenergy levels are 4s, 4p, 4d, and 4f.  If n = 5,
(n – 1) = (n – 5) = 4.
Therefore, l = 0,1,2,3,4. The number of subshells will be 5 but 4s, 4p, 4d, and 4f in these four subshells it is possible to arrange the electrons of all the elements of the periodic table.
Subshell name  Name source  Value of ‘l’  Value of ‘m’ (0 to ± l)  Number of orbital (2l+1)  Electrons holding capacity 2(2l+1) 
s  Sharp  0  0  1  2 
p  Principal  1  −1, 0, +1  3  6 
d  Diffuse  2  −2, −1, 0, +1, +2  5  10 
f  Fundamental  3  −3, −2, −1, 0, +1, +2, +3  7  14 
The orbital number of the ssubshell is one, three in the psubshell, five in the dsubshell and seven in the fsubshell. Each orbital can have a maximum of two electrons.
The subenergy level ‘s’ can hold a maximum of two electrons, ‘p’ can hold a maximum of six electrons, ‘d’ can hold a maximum of ten electrons, and ‘f’ can hold a maximum of fourteen electrons.
Aufbau is a German word, which means building up. The main proponents of this principle are scientists Niels Bohr and Pauli. The Aufbau method is to do electron configuration through the subenergy level.
The Aufbau principle is that the electrons present in the atom will first complete the lowest energy orbital and then gradually continue to complete the higher energy orbital.
The energy of an orbital is calculated from the value of the principal quantum number ‘n’ and the azimuthal quantum number ‘l’. The orbital for which the value of (n + l) is lower is the low energy orbital and the electron will enter that orbital first.
Orbital  Orbit (n)  Azimuthal quantum number (l)  Orbital energy (n + l) 
3d  3  2  5 
4s  4  0  4 
Here, the energy of 4s orbital is less than that of 3d. So, the electron will enter the 4s orbital first and enter the 3d orbital when the 4s orbital is full. The method of entering electrons into orbitals through the Aufbau principle is 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d.
The first two electrons of indium enter the 1s orbital. The sorbital can have a maximum of two electrons. Therefore, the next two electrons enter the 2s orbital.
The porbital can have a maximum of six electrons. So, the next six electrons enter the 2p orbital. The second orbit is now full. So, the remaining electrons will enter the third orbit.
Then two electrons will enter the 3s orbital and the next six electrons will be in the 3p orbital of the third orbit. The 3p orbital is now full. So, the next two electrons will enter the 4s orbital and ten electrons will enter the 3d orbital.
The 3d orbital is now full of electrons. So, the next six electrons enter the 4p orbital. Then next two electrons will enter the 5s orbital and the next ten electrons will enter the 4d orbital.
The 4d orbital is now full of electrons. So, the remaining one electron enters the 5p orbital. Therefore, the indium full electron configuration will be 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{10} 5s^{2} 5p^{1}.
Note: The unabbreviated electron configuration of indium is [Kr] 4d^{10} 5s^{2} 5p^{1}. When writing an electron configuration, you have to write serially.
Indium excited state electron configuration
Atoms can jump from one orbital to another orbital in an excited state. This is called quantum jump. The groundstate electron configuration of indium is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{10} 5s^{2} 5p^{1}.
In the indium groundstate electron configuration, the last electron of the 5p orbital is located in the 4p_{x} suborbitals. We already know that the psubshell has three orbitals. The orbitals are p_{x}, p_{y}, and p_{z} and each orbital can have a maximum of two electrons.
So, the correct electron configuration of indium in the ground state will be 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{10} 5s^{2} 5p_{x}^{1}. When the indium atom is excited, then the indium atom absorbs energy. As a result, an electron in the 5s orbital jumps to the 5p_{y} orbital.
Therefore, the electron configuration of indium(In*) in an excited state will be 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{10} 5s^{1} 5p_{x}^{1} 5p_{y}^{1}. The valency of the element is determined by electron configuration in the excited state. Here, indium has three unpaired electrons. So, the valency of indium is 3.
Indium ion(In^{3+}) electron configuration
The electron configuration shows that the last shell of indium has three electrons. Therefore, the valence electrons of indium are three.
The elements that have 1, 2, or 3 electrons in the last shell donate the electrons in the last shell during bond formation. The elements that form bonds by donating electrons is called cation.
The indium atom donates three electrons in the last shell to form an indium ion(In^{3+}). That is, indium is a cation element.
In – 3e^{–} → In^{3+}
The electron configuration of indium ion(In^{3+}) is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{10}.
This electron configuration shows that the indium ion(In^{3+}) has four shells and the last shell has eighteen electrons and it achieves a stable electron configuration. Indium atom exhibits +3 oxidation state.
Video for Electron configuration of indium and indium ion(In^{3+})
FAQs

What is the symbol for indium?
Ans: The symbol for indium is ‘In’.

How many electrons does indium have?
Ans: 49 electrons.

How do you write the full electron configuration for indium?
Ans: 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{10} 5s^{2} 5p^{1}.

How many valence electrons does indium have?
Ans: Three valence electrons.

What is the valency of indium?
Ans: The valency of indium is 3.