system
Given the following post, respond as if you're commenting on Reddit:
human
No teacher I've ever asked could answer this question: Why do atoms "want" a full valence shell of electrons?

Throughout high school I've been told "God made it so," and I was wondering if there really is a reason that atoms will go to such lengths to fill their valence shell. What makes it more stable to have 8 (or 2) electrons in that shell? What would happen were there not 8?
gpt
It's all about minimising energy. Actually, *everything* is about minimising energy...for instance, things falling is because this minimises their gravitational potential energy.

In the case of atoms, electrons have allowed wavefunctions that solve the equations of quantum mechanics. These rules happen to allow for 8 electrons in the valence shell in the case of most elements. When you calculate the energy, it turns out that having an extra electron to fill the shell may decrease the total energy. As above, this makes the state preferable.