Have you ever seen someone's family tree? It's a picture that shows who their parents, grandparents, and great-grandparents are. A Grotrian diagram is kind of like a family tree, but for the electrons in an atom.
Atoms are like tiny little worlds all on their own, and they're made up of even smaller things called particles. One special kind of particle in atoms is called an electron. The Grotrian diagram shows all the different levels that electrons can be on in an atom, kind of like how people in a family tree can be on different generations.
The different levels that electrons can be on are called energy levels, and the Grotrian diagram shows them as horizontal lines. The lines are stacked on top of each other, with the lowest level at the bottom and the higher levels at the top.
Each energy level has different places where electrons can hang out, like little rooms in a house. These places are called orbitals, and they're shown on the diagram as little boxes on each energy level line.
So, just like a family tree, the Grotrian diagram is a way of organizing and showing all the different parts of an atom. It helps people who study atoms understand how they work and how the electrons interact with each other.