eli5: anti-bonding orbitals, why are they bad, why do they exist.

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Is it not possible to think about anti-bonding electrons using the particle theory? instead of wave? like, two electrons put in a BONDING orbital = good, but how do these anti-bonding orbitals even ARISE, and even more so, why/how are they ‘bad’

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I’ll admit I’m a bit rusty on the topic, because it’s been a while since I studied this, but:

The existance of electron orbitals is a quantum phenomenon, and while you can use simple language and classical analogues for a fairly intuitive picture, ultimately the math and “true” explanation uses the wavefunction. The electron isn’t a little ball orbiting the nucleus, it exists in the “whole” orbital until interacted with. I hope that’s close to the spirit of what you asked.

As for bonding and anti-bonding orbitals, bonding orbitals have a lower energy than the original orbital. That means forming a bond is favourable. Anti-bonding orbitals have a higher energy than the original orbital. Normally that doesn’t mean anything because it’s just empty, but if filled, it might make the molecule have higher total energy than separate atoms, and break up the molecule.

EDIT: I really needed a refresher myself, and this reads pretty nicely

https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_Chem1_(Lower)/09%3A_Chemical_Bonding_and_Molecular_Structure/9.08%3A_Molecular_Orbital_Theory

It also pretty intuitively explains why bonding/anti-bonding orbitals exist: the number of total orbitals between the atoms must be preserved, and they cannot have the same energy, and they are ultimately derive from a wave phenomenon, so one is the effect of construtive and the other of destructive interferance, resulting in a level higher and a level lower than the original.