picometers

Picometer (pm) is a unit of length in the metric system equal to 10^-12 meters. The name combines the prefix pico- (10^-12) with the base unit meter. One picometer is one trillionth of a meter and equals 0.001 nanometers.

Picometers are used to quantify dimensions at atomic and molecular scales, such as bond lengths, atomic radii, and lattice spacings in crystals. In practice, many interatomic distances lie in the tens to hundreds of picometers, while X-ray wavelengths are typically expressed in angstroms or nanometers.

Examples of typical sizes include a carbon–carbon bond length of about 154 pm; covalent radii of light elements ranging from roughly 31 to 120 pm; the Bohr radius about 53 pm; and lattice constants of solids often spanning a few hundred picometers to a couple of nanometers.

Measurement methods for picometer-scale distances include X-ray crystallography, electron diffraction, and high-resolution electron microscopy, such as scanning transmission electron microscopy. Scanning probe techniques and interferometry are also used for precise calibration and nanoscale metrology.

Relationship to other units: 1 meter equals 1×10^12 picometers; 1 nanometer equals 1,000 picometers; 1 picometer equals 0.001 nanometers. An angstrom (Å) equals 0.1 nanometers or 100 picometers.

See also: nanoscale measurement; nanometer; angstrom; femtometer; metric prefixes.