Define $$n_r~:=~n-\ell-1~\geq 0,$$ where $n$ and $\ell$ is the principal and azimuthal quantum number, respectively. Bohr's model works best in the limit

$$ \ell \gg 1 $$

(to get to the semiclassical limit & the correspondence principle), and

$$ n_r \text{ small} $$

(to ensure that the orbital has a well-defined radius).

Define $$n_r~:=~n-\ell-1~\geq 0,$$ where $n$ and $\ell$ is the principal and azimuthal quantum number, respectively. Bohr's model works best in the limit

$$ \ell \gg 1 $$

(to get to the semiclassical limit & the correspondence principle), and

$$ n_r \text{ small} $$

(to ensure that the orbital has a well-defined radius).