Each atom then has a complete outer shell of electrons.
The slideshow shows how a covalent bond forms between a hydrogen atom and a chlorine atom, making hydrogen chloride.
A simple molecule contains only a few atoms, so the sizes of atoms and simple molecules have a similar range of sizes. They are very small, typically around 0.1 nm or 10-10 m across.
Individual atoms and molecules are too small to see even with the strongest light microscope. Some electron microscopes can produce images of atoms and simple molecules.