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> On a slightly different topic: I don't really understand the physics of why electrons don't collapse into the positive nucleus, since positives and negatives

> On a slightly different topic: I don't really understand the physics of why electrons don't collapse into the positive nucleus, since positives and negatives should attract. Good question- this was a clear and troubling problem in the classical atomic models before quantum mechanics. Thinking of electrons as little balls whizzing around, being attracted and repelled by various field forces does seem to lend itself to this question. The current understanding is that since electrons are quantum particles, they can only gain or lose energy through quantized packets, and can only occupy certain energy states. In fact, it's much more accurate to describe electrons by their probability fields, and not as those little balls. Quantum mechanics then describes probability shells called Sommerfeld orbits, where the chance of finding an electron at any given point peaks. Unless energy is added or removed from the system by those aformentioned quantized packets, electrons tend to remain at their respective energy levels and shells.

wcoenen 5y ago
> The current understanding is that since electrons are quantum particles, they can only gain or lose energy through quantized packets Just to clarify. An electron moving freely through a vacuum can move at any speed; it is not restricted to certain energy levels. (Speed and therefore kinetic energy is relative to the reference frame anyway.) The quantization of energy comes into play when the electron is spatially confined in some system. This is related to the wave behavior of the particle, and because energy is related to wavelength. Much like how a standing wave on a string can only have wavelengths such that an integer multiple of them fit on the string.
- IntrepidWorm 5y ago
  Good clarification- my wording was clunky.
danwills 5y ago
Great answer! I'm still left wondering exactly what it is about the behaviour of an electron in the lowest orbit that is stopping it from getting closer to the nucleus. Maybe even thinking of it as 'stopping' at all is my problem. Guess the standing-wave analogy below is actually pretty good for understanding that aspect and also accepting that it's a probability field, which does have nonzero values 'inside' the lowest orbital, so it can be 'found' (measured to be) closer in, just much less often. I'd guess having an intuition about why only the first orbital is spherical is probably part of understanding this all properly too, will keep-on reading!

wcoenen 5y ago

> The current understanding is that since electrons are quantum particles, they can only gain or lose energy through quantized packets Just to clarify. An electron moving freely through a vacuum can move at any speed; it is not restricted to certain energy levels. (Speed and therefore kinetic energy is relative to the reference frame anyway.) The quantization of energy comes into play when the electron is spatially confined in some system. This is related to the wave behavior of the particle, and because energy is related to wavelength. Much like how a standing wave on a string can only have wavelengths such that an integer multiple of them fit on the string.

IntrepidWorm 5y ago
Good clarification- my wording was clunky.

danwills 5y ago

Great answer! I'm still left wondering exactly what it is about the behaviour of an electron in the lowest orbit that is stopping it from getting closer to the nucleus. Maybe even thinking of it as 'stopping' at all is my problem. Guess the standing-wave analogy below is actually pretty good for understanding that aspect and also accepting that it's a probability field, which does have nonzero values 'inside' the lowest orbital, so it can be 'found' (measured to be) closer in, just much less often. I'd guess having an intuition about why only the first orbital is spherical is probably part of understanding this all properly too, will keep-on reading!