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 Electrons and Energy Levels. The electron is one of the most important factors in determining how an atom will react with another atom or molecule. A single electron can make all the difference in the properties of an atom. For example, sodium has one outer electron, located in that 3 s orbital.