When scientists and engineers work at the molecular or atomic level, standard units like the meter become unwieldy. To manage these extremely small distances, the international system of units (SI) uses standardized metric prefixes that modify a base unit by specific powers of ten. Prefixes like nano and pico provide a concise language for communicating measurements in fields ranging from physics and chemistry to materials science.
Understanding the Nanoscale
The prefix “nano” (symbol ‘n’) represents a factor of one billionth, or $10^{-9}$, of a base unit. This scale is the foundation of nanotechnology, which focuses on manipulating matter at dimensions between one and 100 nanometers. Many biological structures exist within this range, such as the double helix of a DNA molecule, which has a diameter of approximately 2 to 2.4 nanometers.
Engineered materials gain unique properties at the nanoscale that are not observed at larger sizes. Nanoparticles, created for applications in medicine and electronics, often have diameters measured in tens of nanometers. Working at this scale allows researchers to design materials with enhanced strength, conductivity, or catalytic activity.
Understanding the Picoscale
The prefix “pico” (symbol ‘p’) denotes one trillionth, or $10^{-12}$, of a base unit. This scale is three orders of magnitude smaller than the nanoscale and is reserved for measurements deep within the atom. While the nanoscale describes molecular arrangements, the picoscale is appropriate for discussing the dimensions of atoms themselves.
Atomic radii, representing the approximate size of an atom’s electron cloud, are commonly measured in picometers (pm). The radius of a hydrogen atom is about 53 pm, and the largest known atomic radius (Cesium) is approximately 260 pm. The distance between the nuclei of two bonded atoms often falls within the range of a few hundred picometers. This level of measurement is fundamental to quantum chemistry and solid-state physics.
Answering the Question: How Much Smaller is Pico?
Pico is the smaller unit. The relationship between the two prefixes is determined by the difference in their powers of ten: nano is $10^{-9}$ and pico is $10^{-12}$. This means pico is smaller by a factor of $10^3$, or 1,000 times. Therefore, one nanometer equals 1,000 picometers.
This thousand-fold difference highlights the distinct domains of science each scale addresses. Nanotechnology focuses on the assembly of large molecules and tiny machines. Conversely, the picoscale is the domain of high-energy physics and precise crystallographic measurements. For example, the size of an entire molecule, such as a protein, might be measured in nanometers, but the precise distance between two individual atoms within that molecule is measured in picometers.