Arches. Photo by Daniel Chia
HOPES: Huntington's Outreach Project for Education, at Stanford
Nov
16
2010

molecule

The smallest unit of matter of a substance that retains all the physical and chemical properties of that substance, consisting of a single atom or a group of atoms bonded together. Example: A single water molecule (H2O) consists of just one single oxygen atom bonded to just two hydrogen atoms. There are billions of billions of water molecules in a single droplet of water. Molecules are too small to be seen without the assistance of powerful microscopes.