Bohr radius

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.