Atoms are extremely small. A typical atom is about 0.1 nanometres (nm) across. One nanometre is 1 × 10-9 m, so the order of magnitude for the size of an atom is 1 × 10-10 m.
Small molecules are made of a few atoms joined together, so they are a little bigger. A small molecule such as water is about 1 nm across, which is 1 × 10-9 m. This is about ten times wider than a single atom, so a small molecule is one order of magnitude larger than an atom. An order of magnitude means a factor of ten.
To picture the scale, a human hair is roughly 1 × 10-4 m wide. That is about a million times wider than an atom, so roughly a million atoms would fit side by side across a hair.