Covalent bonds are formed when two or more atoms share electrons. Each atom contributes one or more electrons to the shared pair, which is then held in a region between the nuclei of the atoms. The strength of the covalent bond depends on the number of electrons shared and the electronegativity of the atoms involved.

Some examples of atoms that are bonded together with covalent bonds include:

- Hydrogen and oxygen: The two atoms share two electrons, forming a single covalent bond.

- Carbon and hydrogen: The four atoms share four electrons, forming four single covalent bonds.

- Nitrogen and oxygen: The two atoms share three electrons, forming a double covalent bond.

- Carbon and oxygen: The two atoms share four electrons, forming a double covalent bond.

Covalent bonds are the strongest type of chemical bond and are found in a wide variety of compounds, including water, methane, and carbon dioxide.