Forming a covalent bond

These shared electrons are found in the outer shells of the atoms. In general, each atom contributes one electron to the shared pair of electrons.

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.

Learn more on covalent bonding in this podcast.

Listen to the full series on BBC Sounds.

Sizes of atoms and simple molecules

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.