Metals are the only substances that use metallic bonds among their atoms. While many elements are commonly known as metals, including iron, aluminum, gold, silver and nickel, metals include a variety of other elements as well. Most elements are metals, including some such as sodium, radium and calcium, which may not seem very metallic.
Metallic bonds are defined as those in which metals share valence electrons. For example, when sodium metallically bonds with itself, each atom is sharing the electrons in the third orbital with up to eight other atoms. The same thing happens when magnesium or other metals metallically bond to themselves.
This type of bond is strong and holds the atoms together securely. This causes metals to have very high melting temperatures and very high boiling temperatures. When a metal melts, the individual atoms lose their strict organization pattern, but the atoms remain bonded together. By contrast, when a metal boils, the atomic bonds break completely.
Some elements are called transitional metals. These types of elements have even higher melting and boiling temperatures than metals do because they share more valence electrons. While metals share electrons in the third orbital, transition metals share third and fourth orbital electrons.