Covalent bonds

Forming a covalent bond

A covalent bond is formed when a pair of electrons is shared between two atoms, usually non-metals.

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.

Structures of a hydrogen atom and a chlorine atom.

1. A hydrogen atom with one electron and a chlorine atom with 17 electrons

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.

Structure of a water moleculeA water molecule is about 0.3 nm across

An explanation of covalent bonding