Video narration
Why don't electrons simply crash into the nucleus? Picture the atom like a Solar System: the nucleus at the centre, like the Sun, and electrons around it like planets. But this picture has a problem. An orbiting object can lose energy and spiral inward. Bohr's key idea changes the picture: electrons are allowed only in certain electron shells, or fixed energy levels, around the nucleus. They cannot stop at any distance. While an electron stays in an allowed shell, it does not lose energy in this model. Give it energy, and it jumps to a higher level. When it drops back, it releases that energy. Bohr's model is useful for learning about atoms, especially hydrogen-like atoms, but it does not describe every atom perfectly. So, why don't electrons crash inward? In Bohr's model, they remain in fixed energy shells, where they do not lose energy.