What does an Angstrom (Å) measure?

The Angstrom (Å) is a unit of length used in science to measure extremely small distances, especially at the atomic and molecular scale. One Angstrom is defined as 10⁻¹⁰ meters, which is also equal to 0.1 nanometers or 100 picometers. Because atoms, molecules, and wavelengths of light fall within this size range, the angstrom is widely used in physics, chemistry, materials science, and crystallography.

The unit was first introduced by the Swedish physicist Anders Jonas Ångström, who studied the spectra of elements in the 19th century. To honor his contributions, this tiny unit was named after him. For example, the radius of a hydrogen atom is about 0.5 Å, and the wavelength of visible light ranges roughly from 4000 Å to 7000 Å.

In physics, the angstrom is often used when describing the spacing between atoms in a crystal lattice, or the wavelength of electromagnetic radiation, such as X-rays and ultraviolet light. In chemistry and biology, bond lengths between atoms in molecules are usually measured in angstroms. For example, the carbon–carbon bond in organic compounds is about 1.54 Å.

Although the angstrom is not part of the official SI (International System of Units), it remains in common use because of its convenience in describing dimensions at the atomic scale. Instead of writing “0.0000000001 meters,” scientists can simply use 1 Å.

In modern scientific practice, nanometers (nm) are increasingly preferred, but the angstrom is still widely recognized and used in textbooks, research papers, and laboratory measurements.

Therefore, the correct answer is that an Angstrom (Å) measures length, particularly at the atomic and molecular scale, making it an important unit in both physics and chemistry.