# Electron Configuration for Chromium (Cr and Cr2+, Cr3+ ions)

Chromium is the 24th element in the periodic table and its symbol is ‘Cr’. In this article, I have discussed in detail how to easily write the complete electron configuration of chromium.

## What is the electron configuration of chromium?

The total number of electrons in chromium is twenty-four. These electrons are arranged according to specific rules in different orbitals.

The arrangement of electrons in chromium in specific rules in different orbits and orbitals is called the electron configuration of chromium.

The electron configuration of chromium is [Ar] 3d^{5} 4s^{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.

## Chromium 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 chromium is 24. That is, the number of electrons in chromium is twenty-four. Therefore, the chromium atom will have two electrons in the first shell and eight in the 2nd shell.

According to Bohr’s formula, the third shell will have fourteen electrons but the third shell of chromium will have thirteen electrons and the remaining one electron will be in the fourth orbit.

Therefore, the order of the number of electrons in each shell of the chromium(Cr) atom is 2, 8, 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 chromium 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 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 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 capacity2(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.

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 chromium 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 the remaining four electrons will enter the 3d orbital.

But the orbital wants to be half-filled or full-filled by electrons. Because the atom may be in a more stable state when the orbital is half-filled and full-filled.

Therefore, an electron of 4s orbital completes a half-filled 3d orbital by jumping into a 3d orbital. So, the chromium full electron configuration will be 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{5} 4s^{1}.

Note:The abbreviated electron configuration of chromium is [Ar] 3d^{5}4s^{1}. When writing an electron configuration, you have to write serially.

## Chromium ion(Cr^{2+}, Cr^{3+}) electron configuration

The ground state electron configuration of chromium is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{5} 4s^{1}. This electron configuration shows that the last shell of chromium has an electron and the d-orbital has a total of five electrons. Therefore, the valence electrons of chromium are six.

There are two types of chromium ions. The chromium atom exhibits Cr^{2+} and Cr^{3+} ions. The chromium atom donates an electron in 4s orbital and an electron in 3d orbital to convert chromium ion(Cr^{2+}).

Cr – 2e^{–} → Cr^{2+}

Here, the electron configuration of chromium ion(Cr^{2+}) is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{4}. The chromium atom donates an electron in 4s orbital and two electrons in 3d orbital to convert to chromium ion(Cr^{3+}).

Cr – 3e^{–} → Cr^{3+}

The electron configuration of chromium ion(Cr^{3+}) is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{3}. Chromium exhibits +2, +3 and +6 oxidation states. The oxidation state of the element changes depending on the bond formation.

## Video for Electron Configuration for Cr, Cr2+, and Cr3+ (Exception to Rules)

## Compound formation of chromium

Chromium participates in the formation of bonds through its valence electrons. We know that the valence electrons in chromium are six.

This valence electron participates in the formation of bonds with atoms of other elements. The electron configuration of chlorine shows that the valence electrons of chlorine are seven.

The chromium atom donates its valence electrons to the chlorine atom and the chlorine atom receives those electrons. As a result, chlorine acquires the electron configuration of argon.

Chromium(III) chloride(CrCl_{3}) is formed by the exchange of electrons between one atom of chromium and three atoms of chlorine. Chromium(III) chloride(CrCl_{3}) is ionic bonding.

## FAQs

### What is the symbol for chromium?

**Ans:**The symbol for chromium is ‘Cr’.### How many electrons does chromium have?

**Ans:**24 electrons.### How do you write the full electron configuration for chromium?

**Ans:**1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{5}4s^{1}.### How many valence electrons does chromium have?

**Ans:**Six valence electrons.### What is the valency of chromium?

**Ans:**The valency of chromium is 2.