# Selenium(Se) electron configuration and orbital diagram

Selenium(Se) is the 34th element in the periodic table and its symbol is ‘Se’. The electron configuration of selenium and the orbital diagram is the main topic in this article. Also, valency and **valence electrons of selenium**, and compound formation, bond formation have been discussed. Hopefully, after reading this article you will know in detail about this.

The total number of electrons in selenium is thirty-four. These electrons are arranged according to specific rules of different orbits. The arrangement of electrons in different orbits and orbitals of an atom in a certain order is called electron configuration. The electron configuration of selenium(Se) atoms can be done in two ways.

- Electron configuration through orbit
- Electron configuration through orbital

Electron configuration through orbitals follows different principles. For example Aufbau principle, Hund’s principle, Pauli’s exclusion principle. There is an article published on this site detailing the **electron configuration**, you can read it if you want.

Table of Contents

## Selenium(Se) 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, N is the name of the fourth orbit. The electron holding capacity of each orbit is 2n^{2}.

For example,

- n = 1 for K orbit.

The electron holding capacity of K orbit is 2n^{2}= 2 × 1^{2}= 2 electrons. - For L orbit, n = 2.

The electron holding capacity of the L orbit is 2n^{2}= 2 × 2^{2}= 8 electrons. - n=3 for M orbit.

The maximum electron holding capacity in M orbit is 2n^{2}= 2 × 3^{2 }= 18 electrons. - n=4 for N orbit.

The maximum electron holding capacity in N orbit is 2n^{2}= 2 × 4^{2}= 32 electrons.

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 selenium(Se) is 34. That is, the number of electrons in selenium is thirty-four. Therefore, the selenium atom will have two electrons in the first shell, eight in the 2nd orbit, eighteen electrons in the 3rd shell, and the remaining six electrons will be in the fourth shell. Therefore, the order of the number of electrons in each shell of the selenium atom is 2, 8, 18, 6.

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 selenium(Se) through orbital

The German physicist Aufbau first proposed an idea of electron configuration through sub-orbits. The Aufbau method is to do electron configuration through the sub-energy level. These sub-orbitals are expressed by ‘l’. 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. These orbitals are named s, p, d, f. The electron holding capacity of these orbitals is s = 2, p = 6, d = 10 and f = 14. The Aufbau electron configuration method is 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d.

The first two electrons of selenium enter the 1s orbital. The s-orbital can have a maximum of two electrons. Therefore, the next two electrons enter the 2s orbital. The p-orbital 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. So, the remaining four electrons enter the 4p orbital. **Therefore, the selenium(Se) electron configuration will be 1s ^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{4}.**

## How to write the orbital diagram for selenium(Se)?

To create an orbital diagram of an atom, you first need to know Hund’s principle and Pauli’s exclusion principle. Hund’s principle is that electrons in different orbitals with the same energy would be positioned in such a way that they could be in the unpaired state of maximum number and the spin of the unpaired electrons will be one-way. And Pauli’s exclusion principle is that the value of four quantum numbers of two electrons in an atom cannot be the same. To write the orbital diagram of selenium(Se), you have to do the electron configuration of selenium. Which has been discussed in detail above.

1s is the closest and lowest energy orbital to the nucleus. Therefore, the electron will first enter the 1s orbital. According to Hund’s principle, the first electron will enter in the clockwise direction and the next electron will enter the 1s orbital in the anti-clockwise direction. The 1s orbital is now filled with two electrons. Then the next two electrons will enter the 2s orbital just like the 1s orbital. The next three electrons will enter the 2p orbital in the clockwise direction and the next three electrons will enter the 2p orbital in the anti-clockwise direction.

The next two electrons will enter the 3s orbital. Then the next six electrons will enter the 3p orbital just like the 2p orbital. The 3p orbital is now full. So, the next two electrons will enter the 4s orbital just like the 1s orbital. The 4s orbital is now full. Therefore, the next five electrons will enter the 3d orbital in the clockwise direction and the next five electrons will enter the 3d orbital in the anti-clockwise direction. The 3d orbital is now full. so, the next three electrons will enter the 4p orbital in the clockwise direction and the remaining one electron will enter the 4p orbital in the anti-clockwise direction. This is clearly shown in the figure of the orbital diagram of selenium.

## Selenium(Se) excited state electron configuration

Atoms can jump from one orbital to another orbital by excited state. This is called quantum jump. Ground state electron configuration of selenium is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{4}. In the selenium ground-state electron configuration, four electrons of the 4p orbital are located in the 4p_{x}(2), 4p_{y} and 4p_{z} sub-orbitals. The p-orbital has three sub-orbitals. The sub-orbitals are p_{x}, p_{y}, and p_{z}. Each sub-orbital can have a maximum of two electrons. Then the correct electron configuration of selenium(Se) in the ground state will be 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p_{x}^{2} 4p_{y}^{1} 4p_{z}^{1}. This electron configuration shows that the last shell of the selenium atom has two unpaired electrons. So in this case, the valency of selenium is 2.

When the selenium atom is excited, then the selenium atom absorbs energy. As a result, an electron in the 4p orbital jumps to the 5s orbital. Therefore, the electron configuration of selenium(Se*) in excited state will be 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p_{x}^{1} 4p_{y}^{1} 4p_{z}^{1} 5s^{1}. The valency of the element is determined by electron configuration in the excited state. Here, selenium has four unpaired electrons. So, the valency of selenium is 4.

## Selenium ion(Se^{2-}) electron configuration

The electron configuration of selenium shows that the last shell of selenium(Se) has six electrons. Therefore, the **valence electrons** of selenium are six. The elements that have 5, 6, or 7 electrons in the last shell receive the electrons in the last shell during bond formation. The elements that receive electrons and form bonds are called anions. During the formation of a bond, the last shell of selenium receives two electrons and turns into a selenium ion(Se^{2-}). That is, selenium is an anion element.

Se + 2e^{–} → Se^{2-}

The electron configuration of selenium ion(Se^{2-}) is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6}. This electron configuration shows that the selenium ion(Se^{2-}) acquired the **electron configuration of krypton**. Selenium atom exhibit -2, +2, +4, +6 oxidation states. The oxidation state of the element changes depending on the bond formation.

## FAQs

What is the symbol for selenium?**Ans:** The symbol for selenium is ‘Se’.

How many electrons does selenium(Se) have?**Ans:** 34 electrons.

How do you write the electron configuration for selenium?**Ans:** Selenium(Se) electron configuration is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{4}.

How many valence electrons does selenium(Se) have?**Ans:** Six valence electrons.

What is the valency of selenium(Se)?**Ans:** The valency of selenium is 2, 4, 6.

**Reference**