Are metals monoatomic or polyatomic in nature? For in crystalline form they also form molecular orbitals.
True metals are held together by the metallic bond. Unlike ionic or covalent bonds, there is no definite ratio of ingredients: for example, electrons are shared throughout an alloy of gold and silver in any proportion.
So, one could consider any intact piece of metal a giant molecule, because electrons are shared throughout, or one could consider it monatomic, because there is no definitive chemical bond amongst the atoms. It all depends on your definition, much like the multiple Lewis, Brønsted - Lowry etc. definitions of "Acid" or "Base".