Though similar to tendons, ligaments connect bone to bone and help to stabilize joints they surround. They are composed mostly of long, stringy collagen fibers that create bands of tough, fibrous connective tissue.
An electron is a negatively charged subatomic particle. It can be either free (not attached to any atom), or bound to the nucleus of an atom. Electrons in atoms exist in spherical shells of various radii, representing energy levels. The larger the spherical shell, the higher the energy contained in the electron.
Valence electron. In chemistry, a valence electron is an electron that is associated with an atom, and that can participate in the formation of a chemical bond; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.