Identify the element that has a ground state electronic configuration of [Kr]5s24d5.
Tc
Mn
Nb
Ru
The correct answer and explanation is :
The element with the ground-state electronic configuration [Kr]5s²4d⁵ is Ruthenium (Ru).
Explanation:
The notation “[Kr]” refers to the electron configuration of Krypton, which corresponds to the noble gas element with atomic number 36. Therefore, the configuration “[Kr]” accounts for the first 36 electrons, leaving the remaining electrons to be placed in higher-energy orbitals.
Now, let’s break down the rest of the configuration:
- 5s²: This means that two electrons occupy the 5s orbital, which is the first available orbital in the fifth energy level.
- 4d⁵: This indicates that five electrons occupy the 4d orbital, which is the next available orbital in the fourth energy level.
To find the element, we count the total number of electrons:
- Krypton (Kr) contributes 36 electrons.
- The 5s² contributes 2 electrons.
- The 4d⁵ contributes 5 electrons.
This gives a total of 36 + 2 + 5 = 44 electrons, meaning the atomic number of the element is 44.
Element number 44 on the periodic table is Ruthenium (Ru), which belongs to the transition metals group.
Why not the other elements?
- Technetium (Tc) has the atomic number 43, with the electronic configuration [Kr]5s²4d⁵. This is very close to the configuration in question but has one less electron than Ruthenium, so it is not the correct answer.
- Manganese (Mn) has the atomic number 25, with the configuration [Ar]4s²3d⁵. This is far different from the given configuration.
- Niobium (Nb) has the atomic number 41, with the configuration [Kr]5s¹4d⁴, which is also different from the configuration in question.
Thus, Ruthenium (Ru) is the correct element with the given ground-state electronic configuration [Kr]5s²4d⁵.