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In page Chemical element:

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Besides being different by physical properties as substances, metallic and nonmetallic elements have different chemical properties as kinds of atoms: metallic elements form simple cations, whereas nonmetallic elements (and weak metals) form simple anions and oxoanions.[2] An exception is noble gases, which do not form simple anions, whereas oxoanions are known for xenon.[3] However, some metallic elements in higher oxidation states form oxoanions as well. Atoms of nonmetallic elements also form compounds with covalent bonds.[citation needed]