According to Bohr's calculations for a hydrogen atom, the electron under normal conditions always stays at a certain distance from the nucleus. This distance is called the Bohr radius and is approximately 0.529 Å (). But according to the wave mechanical or cloud concept model, the electron keeps on moving away or towards the nucleus and the maximum probability of locating it lies at a distance of 0.529 Å from the nucleus. In other words, the radius of the electron cloud or the radius of maximum probability is 0.529 Å.