In a covalent bond, two atoms share one or more electrons. In the case of CH4, the carbon atom shares its four valence electrons with the four hydrogen atoms. This results in a stable molecule in which all of the atoms have a full outer electron shell.

In contrast, an ionic bond is formed when one atom transfers one or more electrons to another atom. This results in two oppositely charged ions. Ionic bonds are typically found in compounds between metals and non-metals.