picometer

The picometer (symbol: pm) is a unit of length in the metric system equal to 10^-12 meters. It is used to express sizes at the atomic and molecular scales. One picometer is equal to one thousandth of a nanometer and one millionth of a micrometer. The unit is commonly used alongside the angström (Å) and nanometer (nm). 1 Å equals 100 pm, while 1 nm equals 1000 pm.

In science, picometers describe interatomic distances, bond lengths, lattice spacings, and atomic radii. For example, typical covalent bond lengths fall in the range of roughly 100–160 pm: C–C about 154 pm, C=C about 134 pm, and C–H about 109 pm. Distances within crystals and in materials science are often given in picometers.

Measurements of picometer-scale dimensions rely on techniques such as X-ray crystallography and electron microscopy to resolve atomic structure, and scanning probe methods like scanning tunneling microscopy (STM) and atomic force microscopy (AFM) for surface features. Spectroscopic methods and dynamical scattering experiments may also infer distances at this scale.

The picometer is an internationally recognized SI unit. In everyday scientific writing, the angström is sometimes used due to historical reasons, but the picometer is the SI equivalent and preferred in formal contexts when precise metric notation is required.