> Photons are basically packets of momentum that atoms exchange.
Is the quantized nature of these packets caused by a limitation in the atoms and their ability to form photons, or is it a fundamental limitation of the photons themselves?
Is the quantized nature of these packets caused by a limitation in the atoms and their ability to form photons, or is it a fundamental limitation of the photons themselves?
The energy of any photon is the Planck constant multiplied by the frequency. The frequency and energy aren't quantized and can be any value as long as they are proportional.
The energy of an electron in an atom isn't quite so simply expressed but is limited to discrete levels.
This is where emission/absorbsion lines come from or to simplify, color.
Electrons can only accept/emit specific amounts of energy and photons of a specific frequency have an exact energy therefore atoms can only absorb or emit very specific frequencies and all others are ignored.
But energy levels in atoms are quantized, and each sort of atom has a distinct set of possible energy levels. And so can emit/absorb a distinct set of possible energy photons. That's what emission/absorption spectra are all about.
Free-electron lasers, conversely, can be built to produce coherent photons of any energy. Albeit constrained by construction methods.
What you're probably referring to is quantization of the electron energy, but I believe that only happens for bound electrons. If an atom loses or gains electrons, things can work quite differently. This is also different for electrons in a metal's conduction band, which are somewhat free, since they are bound to the metal, but not so much to individual atoms.