Bohr Atoms

This solar-system-like visualization of the elements is known as the Bohr model. It was proposed by Niels Bohr in 1913. It is very much just a pretty picture far removed from the more accurate picture of 3d wave functions painted by quantum mechanics.

In fact this 2d visualization is a simplification even of the incorrect Bohr model in which electrons really orbit in 3d around the nucleus. Yet this animation gives an intuitive understanding of how electrons are placed into shells and how electron energies decrease with increasing shell number. To be precise, the radius of electron orbitals increases with the square of the shell number (shown here as linear due to page width constraints). Meanwhile, the 'kinetic energy' of the electrons decreases linearly with shell number.

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