Complete Electron Configuration of Molybdenum (Mo, Mo3+)
Molybdenum is the 42nd element in the periodic table and its symbol is ‘Mo’. In this article, I have discussed in detail how to easily write the complete electron configuration of molybdenum.
What is the electron configuration of molybdenum?
The total number of electrons in molybdenum is fortytwo. These electrons are arranged according to specific rules in different orbitals.
The arrangement of electrons in molybdenum in specific rules in different orbits and orbitals is called the electron configuration of molybdenum.
The electron configuration of molybdenum is [Kr] 4d^{5} 5s^{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.
Molybdenum 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 molybdenum is 42. That is, the number of electrons in molybdenum is fortytwo. Therefore, a molybdenum 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 twelve electrons but the fourth shell of molybdenum will have thirteen electrons and the remaining one electron will be in the fifth shell.
Therefore, the order of the number of electrons in each shell of the molybdenum(Mo) atom is 2, 8, 18, 13, 1. 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 molybdenum 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 molybdenum 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. So, the next six electrons enter the 4p orbital. The 4p orbital is now full. Then the next two electrons will enter the 5s orbital. But the orbital wants to be halffilled or fullfilled by electrons.
Because the atom may be in a more stable state when the orbital is halffilled and fullfilled. Therefore, an electron of the 5s orbital completes a halffilled 4d orbital by jumping into the 4d orbital.
Therefore, the molybdenum complete electron configuration will be 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{5} 5s^{1}. Electron configuration of chromium atoms is done by following this rule.
Note: The unabbreviated electron configuration of molybdenum is [Kr] 4d^{5} 5s^{1}. When writing an electron configuration, you have to write serially.
Molybdenum ion(Mo^{3+}) electron configuration
The ground state electron configuration of molybdenum is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{5} 5s^{1}.
This electron configuration shows that the last shell of molybdenum has an electron and the dorbital has a total of five electrons. Therefore, the valence electrons of molybdenum are six.
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 are called cations.
The molybdenum atom donates an electron in the 5s orbital and two electrons in the 4d orbital to convert a molybdenum ion(Mo^{3+}).
Mo – 3e^{–} → Mo^{3+}
The electron configuration of molybdenum ion(Mo^{3+}) is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{3}.
The electron configuration of a molybdenum ion shows that the molybdenum ion(Mo^{3+}) has four shells and the last shell has eleven electrons.
Molybdenum exhibits +4, +6 oxidation states. The oxidation state of the element changes depending on the bond formation.
Video for Electron Configuration of Molybdenum and Molybdenum ions (Mo3+)
FAQs

What is the symbol for molybdenum?
Ans: The symbol for molybdenum is ‘Mo’.

How many electrons does molybdenum have?
Ans: 42 electrons.

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

How many valence electrons does molybdenum have?
Ans: Six valence electrons. The last shell of molybdenum has an electron and the dorbital has a total of five electrons. Therefore, the valence electrons of molybdenum are six.

What is the valency of molybdenum?
Ans: The valency of molybdenum is 2, 3, 4, 5, and 6.

How many inner valence and outer electrons are present in molybdenum (mo)?
Ans: Molybdenum has a total of six valence electrons. The 5s orbital has an electron and the dorbital has a total of five electrons. That means the inner shell has a total of five valence electrons and the outer shell has an electron.

What is the last entering electron of molybdenum?
Ans: The last entering electron of molybdenum in the 4d orbital. Because the electrons present in the atom will first complete the lowest energy orbital and then gradually continue to complete the higher energy orbital. In the molybdenum atom, the 4d orbital is the highest energy orbital. Therefore, the last electron of molybdenum enters the 4d orbital.

What is the correct groundstate electron configuration for molybdenum?
Ans: The correct ground state electron configuration of molybdenum is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{5} 5s^{1}.

How many core electrons does Mo have?
Ans: 42 electrons. The atomic number of molybdenum is 42. You must never forget that the atomic number and the number of protons and electrons of an element are equal. Therefore, a molybdenum atom contains fortytwo electrons.

How many unpaired electrons does molybdenum (mo) have?
Ans: Six electrons. The electron configuration of molybdenum is [Kr] 4d5 5s1. The subenergy level ‘s’ can hold a maximum of two electrons, and ‘d’ can hold a maximum of ten electrons. In the electron configuration of molybdenum, an unpaired electron has present in the 5s orbital, and five unpaired electrons have present in the 4d orbital.

What is the noble gas configuration for molybdenum?
Ans: The noble gas configuration for molybdenum is [Kr] 4d^{5} 5s^{1}. This electron configuration is also called abbreviated(short) electron configuration.

How many electrons are in the 3d orbital of mo?
Ans: In the molybdenum atom 3d orbital has a total of ten electrons.

How many electrons are in the 4d orbital one atom of mo?
Ans: In the molybdenum atom 4d orbital has a total of five electrons. Because the atom may be in a more stable state when the orbital is halffilled and fullfilled. Therefore, an electron of the 5s orbital completes a halffilled 4d orbital by jumping into the 4d orbital.