In the Bohr model of the structure of an atom, put forward by Niels Bohr in 1913, electrons orbit a central nucleus. The model says that the electrons orbit only at certain distances from the nucleus, depending on their energy. In the simplest atom, that of hydrogen, a single electron orbits, and the smallest possible orbit for the electron, that with the lowest energy, is the one at a distance from the nucleus called the Bohr radius.
The Bohr radius has a value of 5.291772108×10-11 m (i.e. 53 pm), or about half an angstrom.
Technical description
The Bohr radius (a0) is the radius of the lowest energy orbit in the hydrogen atom:
where:
is the permittivity of vacuum
is Dirac's constant or the "reduced Planck's constant"
- me is the electron rest mass
and
- e is the elementary charge
The Bohr radius is often used as a unit in atomic physics, typically in perturbative expansions of wave function solutions.