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Those are the 7 that form diatomic molecules not the only elements that form covalent bonds with other atoms of that element. The s block excluding hydrogen, d block and f block are all metals and are held together with metallic bonds which are a type of covalent bond. Mercury forms weak, transient metallic bonds in its elemental form but robust bonds in the Hg2(2+) dication. Sulfur, Selenium and Tellurium form rings and chains, the former being typically 8 atoms and the latter being hundreds or thousands of atoms in length. Phosphorus is in the form of P4 molecules in white phosphorus and is a network covalent solid in many of its other allotropes. Eg. black phosphorus is a series of stacked undulating chicken wire sheets. Arsenic and Antimony similarly adopt this undulating chicken wire sheet structure as well. Bismuth, lead, polonium, aluminum, gallium, thallium and tin are all metals held together with metallic bonds. Carbon, silicon and germanium commonly form the cubic diamond structure although carbon is most stable as graphite (stacked chicken wire) and can form molecules like fullerene and nanotubes as well as chains (carbyne). Boron tends to form crystals containing icosahedrons. The only elements that rarely react with other elements let alone form covalent bonds with one another in bench stable compounds are the noble gases: Helium, Neon, Argon, Krypton, Xenon and Oganesson.