Metals are a group of chemical elements that have characteristic physical and chemical properties/I%3A__Chemical_Structure_and_Properties/02%3A_Metals/2.01%3A_Introduction_to_Metals)/07%3A_Periodic_Properties_of_the_Elements/7.06%3A_Metals_Nonmetals_and_Metalloids). They are usually crystalline solids with a relatively simple crystal structure distinguished by a close packing of atoms and a high degree of symmetry. Metals are lustrous, malleable, ductile, and good conductors of heat and electricity/I%3A__Chemical_Structure_and_Properties/02%3A_Metals/2.01%3A_Introduction_to_Metals)/07%3A_Periodic_Properties_of_the_Elements/7.06%3A_Metals_Nonmetals_and_Metalloids). They are found naturally in the Earths crust, generally in the form of metal ores, and are associated with many other elements. Approximately three-quarters of all known chemical elements are metals, with the most abundant varieties in the Earths crust being aluminum, iron, calcium, sodium, potassium, and magnesium. The vast majority of metals are found in ores, but a few such as copper, gold, platinum, and silver frequently occur in the free state because they do not readily react with other elements. Metals differ widely in their chemical reactivity, with the most reactive including lithium, potassium, and radium, whereas those of low reactivity are gold, silver, palladium, and platinum.