Atoms can be balanced or unbalanced. If they are unbalanced they act in such a way to become balanced. When atoms join together they form ionic bonds or covalent bonds. The ionic bonds transfer electrons. Covalent bonds, however, share a pair of the atom’s valence electrons. Two atoms attracted to each other based on the number of valence electrons will share the electron in order to balance and stabilize the atoms. This sharing will create a new compound. The simplest covalent bond is formed with Hydrogen gas. One can see another example of a covalent bond uses two chlorine atoms. They can accomplish a stable structure if they share their single unpaired electron.
"Covalent bonding includes many kinds of interaction, including σ-bonding, π-bonding, metal to non-metal bonding, agostic interactions, and three-center two-electron bonds. The term covalent bond dates from 1939."
A chemical compound is formed when two or more atoms join. The compound becomes stable when the energy of the combined atoms is less than the energy of the atoms when they were alone. One type of chemical bond is a covalent bond.
A covalent bond is a chemical bond in which pairs of valence electrons are shared between atoms and other covalent bonds.
Here is an example:
Hydrogen gas forms the simplest covalent bond in the diatomic hydrogen molecule. The halogens such as chlorine also exist as diatomic gases by forming covalent bonds. The nitrogen and oxygen which makes up the bulk of the atmosphere also exhibits covalent bonding in forming diatomic molecules.