What you see in this video is the atomic model proposed by Niels Bohr, who formulated it from 1911–1918. It envisions the atom almost as a miniature solar system, with negatively charged electrons orbiting a positively charged nucleus. In this video we portray the simplest atom — neutral hydrogen.
But there was a problem with this model: Why doesn’t the electron fall into the nucleus? Oppositely charged particles attract each other, so an electron could “orbit” the nucleus, but an electron moving in a circular orbit will radiate energy causing it to lose “altitude” and fall closer to the nucleus on every orbit:
Bohr knew of this issue, and explained the stable orbits with an ad hoc hypothesis. But there was nothing in his hypothesis that was based on first principles. The model worked well enough for the time.
Then, in the 1920s, with the emergence of quantum mechanics, and the recognition of particle-wave duality, the problem was solved by modeling the orbiting electron as a stationary standing wave. The electron was still attracted by the proton, but based on its energy, which determines its wavelength, it had to reside at some finite distance from the proton — occupying what is called an energy level.
This is what it looks like:
This animation is a simplification. The actual standing wave is spread through three dimensions, and constitutes what is called a shell in today’s atomic models. When there are more than one electron involved, it gets a lot more complicated with multiple lobes of standing waves.
So the quantum model of the atom solved the electromagnetic radiation problem of the original Bohr model. It also provided explanations for many observed phenomena in semiconductors, and has made predictions that led to new discoveries. Quantum theory has been extremely successful in describing the behavior of matter. It is still at odds with Einstein’s theory of general relativity, but nonetheless provides a framework for much of today’s technology.
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