Question

When drawing the Bohr Diagram of Potassium with 19 electrons, the valence electron goes in the fourth concentric circle, but third energy level can hold up to 18 electrons? Does it mean that subsequent elements like Scandium will go back to the third energy level?

Answer 1

The Bohr Diagram of potassium shows its 19th electron in the 4s subshell due to the lower energy of 4s compared to 3d orbitals. Calcium also fills the 4s subshell before any electrons enter the 3d orbitals, which start filling with scandium.

Step-by-step explanation:

When drawing the Bohr Diagram for potassium, which has 19 electrons, it's important to recognize that the electronic structure doesn't always follow a straightforward 'fill the next available subshell' pattern. Despite the third energy level theoretically being able to hold up to 18 electrons (if you count the d orbitals), potassium's 19th electron actually enters the 4s subshell.

This is due to the energies of the orbitals; the 4s orbital is lower in energy compared to the 3d orbitals. More precisely, potassium's electron configuration is [Ar]4s¹. This phenomenon continues with calcium (atomic number 20), which has an electron configuration of [Ar]4s², completing the 4s subshell before any electrons are placed in the 3d orbitals. It's not until scandium (atomic number 21) that the 3d orbitals begin to fill.