What is a chemical complex?


I was watching an old [Explosions and Fire video](https://youtu.be/a60UewomiCg) where he talks about BCNP. He mentions it being a complex of a transition metal, but doesn’t really explain what that means.

WIkipedia says that complexes are something that happens when atoms or groups of atoms join to another molecule, but it doesn’t explain how that’s different from a normal compound. It even says that complexes form via ionic and covalent bonds just like compounds do.

Later in the video, Ex&F says that similar compounds based on different metals can take different numbers of ligands. What determines how many ligands a compound can take? Is there something like electron valency happening here, or is it some other property?

In: 1

Bonds are easy to understand when the elements are low in the periodic table. Hydrogen can form one bond. Carbon can form four. Nitrogen can form three. They have small nuclei and few electrons.

Transition metals have larger nuclei and dozens of electrons, so there’s a lot of wiggle room when it comes to bonds. They can make more room at the table if there are extra guests, whereas carbon has one table, four chairs, that’s it.

Complexes are cafeterias. Lots of tables and seating arrangements.