What is the correct configuration for the element Promethium (Pm)?

For the element Promethium (Pm), the correct electron configuration reflects its placement on the periodic table, which specifically aligns with the f-block elements. Promethium is a member of the lanthanide series, primarily occupying the 4f orbital region.

To determine the electron configuration, we start from the noble gas configuration of xenon ([Xe]), which accounts for the first 54 electrons. Promethium has an atomic number of 61, meaning it has a total of 61 electrons. After accounting for the [Xe] core, there are 7 electrons remaining to be placed in the outer shells.

Following the order of increasing energy levels, those electrons fill the 6s orbital first, which can accommodate 2 electrons, and then progress to the 4f orbital. The f orbitals are notably complex and are filled after the s orbitals, both in energy increases visually and according to the Aufbau principle.

For Promethium, the 4f orbital is filled with 5 electrons after the 6s has been filled. Therefore, the correct configuration is [Xe] 6s² 4f⁵.

This understanding highlights the importance of both orbital filling principles and the specific electron configurations associated