Bromine Electron Configuration: [Ar] 3d¹⁰ 4s² 4p⁵ Explained

The electron configuration of bromine is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵ which means that the first two electrons enter the 1s orbital. Since the 1s orbital can hold only two electrons the next two will enter the 2s orbital. The next six electrons enter the 2p subshell. The p subshell can hold a maximum of six electrons. So first we put six electrons in the 2p subshell and then the next two electrons in the 3s orbital.

Since the 3s is now full, the electrons will move to the 3p subshell, where the next six electrons will enter. The 3p subshell is now full. Consequently, the following two electrons will enter the 4s orbital. Since the 4s orbital is full, the next ten electrons will move into the 3d subshell. The 3d subshell is now full. Consequently, the remaining five electrons will enter the 4p subshell.  Hence, the electron configuration of bromine will be 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵.

Bromine is the 35th element in the periodic table and the symbol is ‘Br’. Bromine has an atomic number of 35, which means that its atom has 35 electrons around its nucleus. The electron configuration of bromine refers to the arrangement of electrons in the bromine atom’s orbitals. It describes how electrons are distributed among the various atomic orbitals and energy levels, and provides a detailed map of where each electron is likely to be found.

To understand the mechanism of bromine electron configuration, you need to understand two basic things. These are orbits and orbitals. Also, you can arrange electrons in those two ways. In this article, I have discussed all the necessary points to understand the mechanism of bromine electron configuration, including its ground state, noble gas notation, orbital diagram, valence electrons, and Br⁻ ion configuration. I hope this will be helpful in your study.

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Electron arrangement of Bromine through Bohr Model

The atomic number is the number of electrons in that element. The atomic number of bromine is 35. That is, the number of electrons in bromine is thirty-five. Therefore, the bromine atom will have two electrons in the first shell, eight in the 2nd orbit, eighteen electrons in the 3rd shell, and the remaining seven electrons in the fourth shell. Therefore, the order of the number of electrons in each shell of the bromine(Br) atom is 2, 8, 18, 7.

Electron configuration of Bromine through Aufbau Model

Atomic energy shells are subdivided into sub-energy levels. These sub-energy levels are also called orbital. The most probable region of electron rotation around the nucleus is called the orbital.

The sub-energy levels depend on the azimuthal quantum number. It is expressed by ‘l’. The value of ‘l’ is from 0 to (n – 1). The sub-energy levels are known as s, p, d, and f.

Orbit Number	Value of ‘l’	Number of subshells	Number of orbitals	Subshell name	Electrons holding capacity	Electron configuration
1	0	1	1	1s	2	1s2
2	0 1	2	1 3	2s 2p	2 6	2s2 2p6
3	0 1 2	3	1 3 5	3s 3p 3d	2 6 10	3s2 3p6 3d10
4	0 1 2 3	4	1 3 5 7	4s 4p 4d 4f	2 6 10 14	4s2 4p6 4d10 4f14

Explanation:

• If n = 1,
  (n – 1) = (1–1) = 0
  Therefore, the value of ‘l’ is 0. So, the sub-energy level is 1s.
• If n = 2,
  (n – 1) = (2–1) = 1.
  Therefore, the value of ‘l’ is 0, 1. So, the sub-energy levels are 2s, and 2p.
• If n = 3,
  (n – 1) = (3–1) = 2.
  Therefore, the value of ‘l’ is 0, 1, 2. So, the sub-energy 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 sub-energy 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 sub-shells 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.

Sub-shell 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 s-subshell is one, three in the p-subshell, five in the d-subshell, and seven in the f-subshell. Each orbital can have a maximum of two electrons.

The sub-energy 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 sub-energy 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. Following the Aufbau principle, the sequence of entry of electrons into orbitals is 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p.

Therefore, the complete electron configuration for bromine should be written as 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵.

Note: The abbreviated electron configuration of bromine is [Ar] 3d¹⁰ 4s² 4p⁵. When writing an electron configuration, you have to write serially.

How to write the orbital diagram for bromine

Orbital diagrams are usually represented by boxes. Each box represents an orbital and the arrows within the box represent the position of the electron. The boxes are arranged in order of energy of the orbitals.

The lowest energy orbitals are closest to the nucleus and the higher energy orbitals are progressively further away from the nucleus in order of their energy levels. To write the orbital diagram of bromine, you have to write the orbital notation of bromine. Which has been discussed in detail above.

1s is the closest and lowest energy orbital to the nucleus. Therefore, the electrons will first enter the 1s orbital. According to Hund’s principle, the first electron will enter 1s orbital 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. 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 2p orbital is now full. Then the next two electrons will enter the 3s orbital just like the 1s orbital. Then the next three electrons will enter the 3p orbital in the clockwise direction and the next three electrons will enter the 3p orbital in the anti-clockwise direction.

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 two electrons will enter the 4p orbital in the anti-clockwise direction. This is clearly shown in the figure of the orbital diagram of bromine.

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Electron configuration of bromine in the excited state

Atoms can jump from one orbital to another orbital in an excited state. This is called a quantum jump. The ground state electron configuration of bromine is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵. In the bromine ground-state electron configuration, the last five electrons of the 4p orbital are located in the 4p_x(2), 4p_y(2), and 4p_z orbitals. The p-subshell has three orbitals.

The orbitals are p_x, p_y, and p_z and each orbital can have a maximum of two electrons. Then the correct electron configuration of bromine in the ground state will be 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p_x² 4p_y² 4p_z¹. This electron configuration shows that the last shell of a bromine atom has an unpaired electron. So in this case, the valency of bromine is 1.

When the bromine atom is excited, then the bromine atom absorbs energy. As a result, an electron in the 4p_y orbital jumps to the 4d_xy orbital. We already know that the d-subshell has five orbitals. The orbitals are d_xy, d_yz, d_zx, d_x²-y² and d_z² and each orbital can have a maximum of two electrons.

Therefore, the electron configuration of bromine(Br*) in an excited state will be 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p_x² 4p_y¹ 4p_z¹ 4d_xy¹. The valency of the element is determined by electron configuration in the excited state. Here, bromine has three unpaired electrons. So in this case, the valency of bromine is 3.

Bromide ion(Br^–) electron configuration

The electron configuration of bromine shows that the last shell of bromine has seven electrons. Therefore, the valence electrons of bromine are seven. 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 bromine receives an electron and turns into a bromide ion(Br^–). That is, bromine is an anion element.

Br + e^– → Br^–

The electron configuration of bromide ion(Br^–) is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶. The electron configuration of the bromide ion(Br–) shows that the bromide ion acquired the electron configuration of krypton. Bromine atoms exhibit -1, +1, +3, +5 oxidation states. The oxidation state of the element changes depending on the bond formation.