A unit of length equal to one ten-billionth of a meter, used for atomic-scale distances.The angstrom is a unit of length equal to one ten-billionth of a meter (10⁻¹⁰ meters), a scale perfectly suited for measuring the distances between atoms in molecules and crystals. It is named after the Swedish physicist Anders Jonas Ångström, who used it in 1868 to map the wavelengths of light from the Sun. Because atomic radii and bond lengths typically range from one to three angstroms, this unit has become a standard in chemistry, solid-state physics, and crystallography for describing the structure of matter at its most fundamental level.
The unit was proposed by the Swedish physicist Anders Jonas Ångström in his 1868 study of the solar spectrum, where he measured wavelengths in units of 10⁻¹⁰ meters. It was officially adopted as a unit of length in the early 20th century, though it has been largely superseded by the picometer and nanometer in modern SI-based practice.
The angstrom is simply a convenient scale factor: one angstrom equals 100 picometers or 0.1 nanometers. It is not a fundamental physical constant but a human-defined unit that matches the natural spacing of atoms. When scientists use X-ray diffraction or scanning probe microscopy to determine the positions of atoms in a material, they report the results in angstroms because the numbers are easy to grasp—a bond length of 1.5 Å is immediately understood as a typical covalent bond, whereas 150 pm requires a moment's thought.
The angstrom is used in crystallography to describe the spacing of atomic planes in crystals, in chemistry to express bond lengths and ionic radii, and in semiconductor manufacturing to specify the thickness of thin films and the size of features on microchips.
The diameter of a hydrogen atom is about 1.06 angstroms, making it one of the few atoms whose size is almost exactly one angstrom.
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