DNA

Most molecules are far too small to be seen with the naked eye, but there are exceptions. DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers. The smallest molecule is the diatomic hydrogen (H₂), with an overall length of roughly twice the 74 picometres (0.74 Ã…) bond length. Molecules commonly used as building blocks for organic synthesis have a dimension of a few Ã… to several dozen Ã…. Single molecules cannot usually be observed by light (as noted above), but small molecules and even the outlines of individual atoms may be traced in some circumstances by use of an atomic force microscope. Some of the largest molecules are macromolecules or supermolecules.

Radius

Effective molecular radius is the size a molecule displays in solution. The table of permselectivity for different substances contains examples.