<P> Homonuclear molecules, or homonuclear species, are molecules composed of only one type of element . Homonuclear molecules may consist of various numbers of atoms, depending on the element's properties . Some elements form molecules of more than one size . Noble gases rarely form bonds, so they only have one atom . The most familiar homonuclear molecules are diatomic, meaning they consist of two atoms, though not all diatomic molecules are homonuclear . Homonuclear diatomic molecules include hydrogen (H), oxygen (O), nitrogen (N) and all of the halogens . Ozone (O) is a common triatomic homonuclear molecule . Homonuclear tetratomic molecules include arsenic (As) and phosphorus (P). </P> <P> Allotropes are different chemical forms of the same element (not containing any other element). In that sense, allotropes are all homonuclear . Many elements have multiple allotropic forms . In addition to the most common form of gaseous oxygen, O, and ozone, there are other allotropes of oxygen . Sulfur forms several allotropes containing different numbers of sulfur atoms, including diatomic, triatomic, hexatomic and octatomic (S, S, S, S) forms, though the first three are rare . The element carbon is known to have a number of homonuclear molecules, the best known being buckminsterfullerene or "buckyball" </P>

Show the formation of a named homonuclear covalent molecules