Which is the configuration of Cr?
Correct answer: B. [Ar] 3d5 4s1
- A. [Ar] 3d4 4s2
- B. [Ar] 3d5 4s1
- C. [Ar] 3d6 4s1
- D. [Ar] 3d1 4s2
Explanation
It is [Ar] 3d⁵ 4s¹This happens in Cr, as one 4s electron moves to the 3d sublevel. But why? There are two main reasons:The 3d orbital is slightly lower in energy, and minimizing repulsions in the 4s orbital by moving one of the 4s electrons to a close-lying 3d orbital minimizes the ground-state energy of chromium.Hund's Rule: It is energetically favorable to maximize the spin state in a sublevel. Since two opposite spins result in a total spin of 0, maximizing this tends to require as many electrons of the same spin in different orbitals as possible. So, in this case, an electron moves to 3d and is unpaired, therefore maximizing the spin state.
Last updated
About Electronic Configuration
Electronic configuration describes how electrons occupy shells, subshells and orbitals around an atom. Questions use the Aufbau principle, Pauli exclusion principle and Hund's rule to write configurations, identify valence electrons, form ions and explain periodic trends, including common exceptions such as chromium and copper.
Practise Atomic Structure
922 free Atomic Structure MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Exams that ask Chemistry questions like this
Chemistry is on 12 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
Related questions
A neutral atom A has the electronic configuration: 1s2 2s2 2p6 3s2 3p6 4s1. It will gain or lose electron/s to form most probably an ion of valence:
According to Hund's rule, electrons entering a set of degenerate orbitals will
According to molecular orbital theory, which one of the following will indicate two unpaired electrons?
According to the n plus l rule, which orbital is filled first?
After 3s the sub-shell begin to fill is