A water molecule is an example of the single covalent bond between oxygen and hydrogen.

Take a look at water (H₂O). H₂O is a MOLECULE, a discrete unit of atoms that are bonded together. A molecule of water consists of an oxygen atom that is bonded to two hydrogen atoms. A hydrogen atom and the oxygen atom each donate one valence electron to form a chemical bond. These two valence electrons forming the bond are shared by both atoms, resulting in a SINGLE COVALENT BOND. Think of this in terms of two pieces of wood that are nailed together. The pieces of wood are the atoms, and the nails holding them together are the electrons that form the covalent bond. Each piece of wood shares a portion of the nails.

Oxygen molecules shares two electrons to make a double covalent bond.

Air, too, contains oxygen. Oxygen does not exist as a single oxygen atom, but as a molecule of two oxygen atoms. These two oxygen atoms share two pairs of valence electrons (four valence electrons total) between them, forming a DOUBLE COVALENT BOND. This is true of any double covalent bond; four valence electrons are shared between two atoms.

In a molecule of carbon, two atoms share three electrons -- a triple covalent bond.

Another component of air is nitrogen. Like oxygen, nitrogen does not exist as a single nitrogen atom, but as a molecule made up of two nitrogen atoms. The two nitrogen atoms in a molecule of nitrogen share three pairs of valence electrons (six valence electrons total) to form a TRIPLE COVALENT BOND.

Is it possible to predict whether bonds are covalent or not? A good rule of thumb is that bonds between nonmetals (remember that hydrogen is considered a nonmetal) are usually covalent bonds. For example, the carbon dioxide (CO₂) molecules you exhale are bonded together covalently.

So you see, you are surrounded, but it's okay. Relax. Take a deep breath. Get a drink of water, maybe. Then read on to learn about some other ways molecules stick together.