In
Bohr's model of the
hydrogen atom, the
Bohr radius (<math>a_0</math>) is the radius of the lowest energy orbit:
<math>a_0 = {{4\pi\epsilon_0\hbar^2}\over{m_e e^2}}</math>
where:
- <math>\epsilon_0</math> is the permittivity of vacuum
- <math>\hbar</math> is the Planck's constant
- <math>m_e</math> is the electron rest mass
and
- <math>e</math> is the elementary charge
It has a value of 5.29189379×10-11 m, or about half an angstrom.