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An italic a with a nought subscript, the atomic length scale.
Also known as: Bohr radius, a nought, Atomic unit of length
The Bohr radius is roughly the size of a hydrogen atom in its ground state, and it is the natural unit of length for atomic physics. It comes from a model now known to be wrong, and it survives because the number it gives is still the right scale.
Denotes the Bohr radius, the most probable electron–proton distance in ground-state hydrogen.
Contexts: Laboratory
Originates in Bohr's 1913 orbital model, which quantum mechanics superseded; the quantity survived the model because it remains the correct atomic length scale.
Contexts: Laboratory
Is the length unit of the atomic unit system, in which many quantum chemistry results are reported.
Contexts: Laboratory
An italic lowercase letter a with a small numeral zero set below and to the right.