system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a change in the number of protons/neutrons/electrons drastically change a molecules properties?

It's like I add a few electrons and neutrons and protons and BOOM, went from hydrogen to copper or copper to neon.

How does a simple change in a molecule's structure determine the chemical and physical properties of an atom?
gpt
The structure is what determines how it interacts with everything around it. 

Think of a molecule like a key, and the rest of the universe is a set of keyholes.  The protons and electrons and neutrons---their positions, charge, number, and other properties---are like the grooves and teeth on the key.  If you change those things in even a small way, it will dramatically alter what keyholes the key will fit.