How to Write the Electron Configuration for Magnesium (Mg)
Magnesium is the 12th element in the periodic table and the symbol is ‘Mg’. The atomic number of magnesium is 12, which means its atom has twelve electrons around its nucleus.
To write the electron configuration for magnesium, the first two electrons enter the 1s orbital. Since the 1s orbital can hold only two electrons the next two enter the 2s orbital. The next six electrons enter the 2p subshell. The p subshell can hold a maximum of six electrons. Hence, the remaining two electrons enter the 3s orbital. Therefore, the electron configuration of magnesium will be 1s2 2s2 2p6 3s2.
The electron configuration of magnesium refers to the arrangement of electrons in the magnesium 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 magnesium 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 magnesium electron configuration. I hope this will be helpful in your study.
Electron arrangement for Magnesium 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 and provided a complete idea of orbit in that model.
The electrons of the atom revolve around the nucleus in a certain circular path. These circular paths are called orbits (shells or energy levels). These orbits are expressed by n. [n = 1,2,3,4 . . . The serial number of the orbit]
The name of the first orbit is K, 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 2n2.
| Shell Number (n) | Shell Name | Electrons Holding Capacity (2n2) |
| 1 | K | 2 |
| 2 | L | 8 |
| 3 | M | 18 |
| 4 | N | 32 |
Explanation:
- Let, n = 1 for K orbit. So, the maximum electron holding capacity in the K orbit is 2n2 = 2 × 12 = 2 electrons.
- n = 2, for L orbit. The maximum electron holding capacity in the L orbit is 2n2 = 2 × 22 = 8 electrons.
- n=3 for M orbit. The maximum electron holding capacity in the M orbit is 2n2 = 2 × 32 = 18 electrons.
- n=4 for N orbit. The maximum electron holding capacity in N orbit is 2n2 = 2 × 42 = 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 magnesium is 12. That is, the number of electrons in magnesium is twelve. Therefore, the magnesium atom will have two electrons in the first shell, eight in the 2nd shell, and two in the 3rd shell. Hence, the order of the number of electrons in each shell of a magnesium(Mg) atom is 2, 8, 2.
The Bohr atomic model has many limitations. In the Bohr atomic model, the electrons can only be arranged in different shells but the exact position, orbital shape, and spin of the electron cannot be determined.
Also, electrons can be arranged correctly from 1 to 18 elements. The electron arrangement of any element with atomic number greater than 18 cannot be accurately determined by the Bohr atomic model following the 2n2 formula. We can overcome all limitations of the Bohr model following the electron configuration through orbital.
Electron configuration of Magnesium through orbital
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 magnesium should be written as 1s2 2s2 2p6 3s2.
Note: The unabbreviated electron configuration of magnesium is [Ne] 3s2. When writing an electron configuration, you have to write serially.
Magnesium ion(Mg2+) Electron configuration
The ground state electron configuration of magnesium is 1s2 2s2 2p6 3s2. After the electron configuration, the last shell of the magnesium atom has two electrons. Therefore, the valency and valence electrons of magnesium are 2.
The elements that have 1, 2, or 3 electrons in the last shell donate the electrons in the last shell during bond formation. Magnesium donates the electron of the last shell to form bonds and turns into a magnesium ion(Mg+2). The elements that form bonds by donating electrons are called cations. That is, magnesium is a cation element.
Mg – 2e– → Mg2+
The electron configuration of magnesium ion(Mg+2) is 1s2 2s2 2p6. This electron configuration shows that magnesium ion(Mg+2) has acquired the electron configuration of neon and it achieves an octave full stable electron configuration.
How many filled s orbitals does magnesium have?
Magnesium (Mg) has three filled s orbital. The s orbitals can hold a maximum of 2 electrons, and the electron configuration of magnesium is 1s2 2s2 2p6 3s2. This means that the 1s orbital is filled with 2 electrons, while the 2s and 3s orbital are also filled with 2 electrons. Therefore, magnesium has three filled s orbital.