ELI5: Explain Like I'm 5

Hund's cases

Hey there kiddo! Today, I'm going to explain something called "Hund's cases". So, imagine you have a bunch of toys that you want to put on a shelf. But, you can't put more than two toys on each shelf. Now, imagine you have different types of toys, like cars, dolls, and blocks.

Here's where Hund's cases come in! Hund's cases help us figure out how we can arrange those toys on the shelves in the best way possible. It all depends on how many toys we have in total and what types they are.

There are three Hund's cases:

1. First Hund's case: It's like having only one shelf and we need to put all the toys on that one shelf. We can arrange them in such a way that each shelf, or energy level, gets one toy before any level has two toys. So, we'll fill one toy in each energy level before we put two toys in one energy level.

2. Second Hund's case: It's like having two shelves where we can put the toys. We can put one toy on each shelf first and then come back to put the second toy on the first shelf, and then the third toy on the second shelf.

3. Third Hund's case: Again, it's like having two shelves, but this time we can put more than one toy on each shelf. We fill the first shelf before we put the second toy on one of the shelves.

So that's what Hund's cases are all about. They help us understand how to arrange the electrons in an atom in the best way possible. And just like how we can't put more than two toys on a shelf, there are rules on how many electrons can go into each energy level in atoms. But, we'll leave that for another time!