Metals are elements defined by characteristic properties: they are lustrous, highly conductive of heat and electricity, and physically malleable. Over 90 of the 118 elements on the periodic table are classified as metals, but there is no single, definitive number of “types.” Categorization depends entirely on the criteria used, such as chemical behavior, physical properties like density, or economic value and industrial application. Understanding these different groupings provides a comprehensive answer to how many types exist.
The Primary Chemical Categories of Metals
The most fundamental way to categorize metals is by their position on the periodic table, which dictates their electron configuration and chemical reactivity. Metals on the far left are the most reactive, exhibiting a strong tendency to lose their valence electrons. This forms the basis for the four main chemical groupings: alkali, alkaline earth, transition, and post-transition metals.
Alkali metals, found in Group 1, are the most chemically reactive of all metals because they readily lose their single outermost electron to form a positive ion. This group includes elements like sodium and potassium, which are soft enough to be cut with a knife and have relatively low densities and melting points. Due to their extreme reactivity, they are never found in their pure elemental form in nature and must be stored under oil in a laboratory setting.
Alkaline earth metals are located in Group 2 and are slightly less reactive than their Group 1 neighbors, though still highly reactive overall. They possess two valence electrons, which they shed to form ions with a +2 charge. Elements in this group, such as magnesium and calcium, are generally harder, denser, and have higher melting points compared to the alkali metals.
The central block of the periodic table is occupied by the transition metals, characterized by having multiple possible oxidation states, allowing them to form a wide variety of compounds. This large group includes familiar structural and coinage metals, such as iron, copper, and gold. Transition metals typically exhibit high melting and boiling points, forming strong metallic bonds that make them hard and strong. Many are also used as catalysts because their variable oxidation states allow them to facilitate chemical reactions.
The post-transition metals are located in the p-block, near the line separating metals from nonmetals, and display a mix of metallic and non-metallic characteristics. These metals, which include aluminum and lead, generally have lower melting points than the transition metals. For example, aluminum melts at about 660 degrees Celsius, significantly lower than the melting point of iron.
Classifications Based on Density and Industrial Use
Beyond chemical classification, metals are often grouped according to physical properties, specifically density, and by their primary industrial application. The density-based system separates metals into light and heavy metals. Light metals have a relatively low density, often cited as less than 5 grams per cubic centimeter, and commercially important examples include aluminum and magnesium.
Aluminum, for instance, has a density of about 2.7 grams per cubic centimeter, making it desirable for applications requiring a high strength-to-weight ratio, such as in aerospace and automotive components. Heavy metals, conversely, have a relatively high density, often exceeding 5 grams per cubic centimeter. Examples include lead, mercury, and cadmium, many of which are of environmental concern.
Industrial use introduces another common distinction: ferrous versus non-ferrous metals. Ferrous metals are defined by their primary component being iron, which provides them with high tensile strength and magnetic properties. Steel and cast iron are common examples of ferrous alloys, forming the backbone of construction and heavy industry. The major drawback of ferrous metals is their tendency to rust when exposed to moisture.
Non-ferrous metals contain little or no iron, making them inherently more resistant to corrosion and generally lighter than their ferrous counterparts. This group includes metals like copper, aluminum, and titanium, valued for their superior electrical conductivity and low weight. Non-ferrous metals are essential for electronics, high-performance vehicles, and specialized plumbing systems.
The Groupings of Precious, Noble, and Rare Earth Metals
A third system of classification is based on economic value and chemical non-reactivity, leading to the distinct groupings of precious, noble, and rare earth metals. Precious metals are defined primarily by their high economic value, rarity, and historical use as currency and investment vehicles. Gold, silver, and platinum are the most widely recognized precious metals, valued for their durability and attractive luster.
Noble metals are defined by their exceptional resistance to corrosion and oxidation, even at high temperatures, meaning they do not readily tarnish or react. This group largely overlaps with precious metals, including gold, platinum, rhodium, and palladium. They are prized for their non-reactive nature in electronics and catalytic converters. The classification is based on chemical stability rather than market price.
The rare earth elements (REEs) are a distinct grouping of 17 chemically similar metallic elements, comprising the lanthanide series plus yttrium and scandium. Despite their name, these elements are rarely found in concentrated, easily mineable deposits. REEs are primarily categorized by their unique magnetic, optical, and phosphorescent properties. They are indispensable for modern technology, forming the basis of strong permanent magnets in electric vehicles and wind turbines, as well as the screens in smartphones and televisions.