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.
In chemistry, an unpaired electron is an electron that occupies an orbital of an atom singly, rather than as part of an electron pair. Each atomic orbital of an atom (specified by the three quantum numbers n, l and m) has a capacity to contain a maximum of two electrons with opposite spins, an electron pair.