Atoms are extremely small. The typical radius of an atom is about 1 × 10-10 metres. We say that atomic radii are "in the order of" 10-10 m, which means the size is about that power of ten.
The distance between the nuclei of two bonded atoms is called the bond length. Bond lengths are also in the order of 1 × 10-10 m, because the bonded atoms are very close together.
A small molecule is only a few atoms joined together, so it is only a few times bigger than one atom. Its size is therefore close to the same order of magnitude.
A nanometre (nm) is 1 × 10-9 m. This means 1 × 10-10 m is 0.1 nm, which is often a more convenient way to write atomic sizes.