Question

Why is the Bohr model obsolete and what can it still be used for?

Answer 1

The Bohr model of the atom is obsolete for most intents and purposes, though it is still used for describing atomic spectra, for example.

Electrons don't really move in discrete orbits. They move pseudo-randomly, and whenever they would theoretically come in contact with another electron, they instantaneously repel each other.

With hydrogen-like atoms, that event doesn't happen. In a hydrogen-like atom, such as `"He"^(+)` or `"Li"^(2+)`, which has only one electron, there is no such repulsive coulombic interactions that cause instantaneous repulsions.

However, when you have more than one electron, it complicates the electron's motion; chemists get all in a rut because of that instantaneous repulsion, which changes the ground-state energy `E` of that element pseudo-randomly, and it becomes impossible to directly calculate it exactly by conventional means.

So now we computationally approximate it in many different ways and try to get it as accurate as possible.