 In 1925, Lewis de Broglie came up with the model that explained how electrons avoid falling into the nucleus. Earlier, we calculated the circumference and velocity of the electron. So, like we did for electron microscopes in the previous segment, he calculated its wavelength. He found that it was exactly the length of the electron orbit's circumference as enumerated by Bohr. In other words, the wavelength of the electron is exactly the length of one revolution. This would create a standing wave. Here are a couple of standing waves on a string. Here's what a standing wave looks like in water. A standing wave is a wave constrained to vibrate in a distance that's exactly one multiple of its wavelength. Standing more or less would create destructive interference and the wave would collapse. So the first energy shell would have to have the radius that creates the circumference that exactly fits one wave. The second shell would have to have the radius that creates the circumference that exactly fits two wavelengths. The third shell would have to have the radius that creates the circumference that exactly fits three wavelengths, and so on. So De Bruy answered the question, how can the electrons sit way outside the nucleus without orbiting away its energy? The answer is that the electrons exist as standing waves that envelop the nucleus. No orbital motion is required, and therefore no radiation is emitted. So it's important to remember, electrons in an atom do not orbit the nucleus. They are not like planets around the sun. They exist as standing waves. De Bruy's simple geometry elegantly explained the reason for each energy shell's distance from the center and its corresponding energy. But it didn't scale to explain the spectra of more complex atoms that have more electrons.