Everyone at that time imagined the atom as a ... the electrons in his model lined up with the regular patterns (spectral series) of light emitted by real hydrogen atoms. Bohr's theory that ...

For example, according to classical physics, the electrons orbiting the nucleus should lose energy until they spiral down into the center, collapsing the atom. Bohr proposed adding to the model ...

An element's atomic number defines it. An element with 17 protons will always be chlorine. However an element's mass numbers can vary, which means that it can have different numbers of neutrons.