A metal (from Greek μέταλλον métallon, "mine, quarry,
metal") is a material (an element, compound, or alloy) that is
typically hard when in solid state, opaque, shiny, and has good
electrical and thermal conductivity. Metals are generally
malleable—that is, they can be hammered or pressed permanently out
of shape without breaking or cracking—as well as fusible (able to be
fused or melted) and ductile (able to be drawn out into a thin
wire). Around 90 of the 118 elements in the periodic table are
metals; the others are nonmetals or metalloids, though elements near
the boundaries of each category have been assigned variably to either
(hence the lack of an exact count). Some elements appear in both
metallic and non-metallic forms.
Astrophysicists use the term "metal" to refer collectively to all
elements in a star that are heavier than the lightest two, hydrogen
and helium, and not just traditional metals. A star fuses lighter
atoms, mostly hydrogen and helium, to make heavier atoms over its
lifetime. Used in that sense, the metallicity of an astronomical
object is the proportion of its matter made up of the heavier chemical
Many elements and compounds that are not normally classified as metals
become metallic under high pressures; these are formed as metallic
allotropes of non-metals, for example, physicists were able to keep
hydrogen in its solid state under more than 3 million times the
atmospheric pressure and deduce its metallic properties.
The strength and resilience of metals has led to their frequent use in
high-rise building and bridge construction, as well as most vehicles,
many home appliances, tools, pipes, non-illuminated signs and railroad
tracks. Precious metals were historically used as coinage.
1 In the periodic table
2 Structure and bonding
5.1 Base metal
5.2 Ferrous metal
5.3 Noble metal
5.4 Precious metal
5.5 Heavy metal
12 See also
14 External links
In the periodic table
The elements which are considered as metals under ordinary conditions
are shown in yellow on the periodic table below. The remaining
elements are shown either as nonmetals or as metalloids of
Metals–nonmetals in the periodic table
Nonmetal Unknown properties Background color shows
metal–metalloid–nonmetal trend in the periodic table
Structure and bonding
hcp and fcc close-packing of spheres
The atoms of metallic substances are typically arranged in one of
three common crystal structures, namely body-centered cubic (bcc),
face-centered cubic (fcc), and hexagonal close-packed (hcp). In bcc,
each atom is positioned at the center of a cube of eight others. In
fcc and hcp, each atom is surrounded by twelve others, but the
stacking of the layers differs. Some metals adopt different structures
depending on the temperature.
Atoms of metals readily lose their outer shell electrons, resulting in
a free flowing cloud of electrons within their otherwise solid
arrangement. This provides the ability of metallic substances to
easily transmit heat and electricity. While this flow of electrons
occurs, the solid characteristic of the metal is produced by
electrostatic interactions between each atom and the electron cloud.
This type of bond is called a metallic bond.
Crystal structures for some metals are listed in the table below
Atomic Radius (nm)
Metals are usually inclined to form cations through electron loss,
reacting with oxygen in the air to form oxides over various timescales
(iron rusts over years, while potassium burns in seconds). Examples:
4 Na + O2 → 2 Na2O (sodium oxide)
2 Ca + O2 → 2 CaO (calcium oxide)
4 Al + 3 O2 → 2 Al2O3 (aluminium oxide).
The transition metals (such as iron, copper, zinc, and nickel) are
slower to oxidize because they form a passivating layer of oxide that
protects the interior. Others, like palladium, platinum and gold, do
not react with the atmosphere at all. Some metals form a barrier layer
of oxide on their surface which cannot be penetrated by further oxygen
molecules and thus retain their shiny appearance and good conductivity
for many decades (like aluminium, magnesium, some steels, and
titanium). The oxides of metals are generally basic, as opposed to
those of nonmetals, which are acidic. Exceptions are largely oxides
with very high oxidation states such as CrO3, Mn2O7, and OsO4, which
have strictly acidic reactions.
Painting, anodizing or plating metals are good ways to prevent their
corrosion. However, a more reactive metal in the electrochemical
series must be chosen for coating, especially when chipping of the
coating is expected. Water and the two metals form an electrochemical
cell, and if the coating is less reactive than the coatee, the coating
actually promotes corrosion.
Metals in general have high electrical conductivity, high thermal
conductivity, and high density. Typically they are malleable and
ductile, deforming under stress without cleaving. In terms of
optical properties, metals are shiny and lustrous. Sheets of metal
beyond a few micrometres in thickness appear opaque, but gold leaf
transmits green light.
Although most metals have higher densities than most nonmetals,
there is wide variation in their densities, lithium being the least
dense solid element and osmium the most dense. The alkali and alkaline
earth metals in groups I A and II A are referred to as the light
metals because they have low density, low hardness, and low melting
points. The high density of most metals is due to the tightly
packed crystal lattice of the metallic structure. The strength of
metallic bonds for different metals reaches a maximum around the
center of the transition metal series, as those elements have large
amounts of delocalized electrons in tight binding type metallic bonds.
However, other factors (such as atomic radius, nuclear charge, number
of bonds orbitals, overlap of orbital energies and crystal form) are
involved as well.
Filling of the electronic states in various types of materials at
equilibrium. Here, height is energy while width is the density of
available states for a certain energy in the material listed. The
shade follows the Fermi–Dirac distribution (black = all states
filled, white = no state filled). In metals and semimetals the Fermi
level EF lies inside at least one band. In insulators and
Fermi level is inside a band gap; however, in
semiconductors the bands are near enough to the
Fermi level to be
thermally populated with electrons or holes.
The electrical and thermal conductivities of metals originate from the
fact that their outer electrons are delocalized. This situation can be
visualized by seeing the atomic structure of a metal as a collection
of atoms embedded in a sea of highly mobile electrons. The electrical
conductivity, as well as the electrons' contribution to the heat
capacity and heat conductivity of metals can be calculated from the
free electron model, which does not take into account the detailed
structure of the ion lattice.
When considering the electronic band structure and binding energy of a
metal, it is necessary to take into account the positive potential
caused by the specific arrangement of the ion cores—which is
periodic in crystals. The most important consequence of the periodic
potential is the formation of a small band gap at the boundary of the
Brillouin zone. Mathematically, the potential of the ion cores can be
treated by various models, the simplest being the nearly free electron
Mechanical properties of metals include ductility, i.e. their capacity
for plastic deformation. Reversible elastic deformation in metals can
be described by
Hooke's Law for restoring forces, where the stress is
linearly proportional to the strain. Forces larger than the elastic
limit, or heat, may cause a permanent (irreversible) deformation of
the object, known as plastic deformation or plasticity. This
irreversible change in atomic arrangement may occur as a result of:
The action of an applied force (or work). An applied force may be
tensile (pulling) force, compressive (pushing) force, shear, bending
or torsion (twisting) forces.
A change in temperature (heat). A temperature change may affect the
mobility of the structural defects such as grain boundaries, point
vacancies, line and screw dislocations, stacking faults and twins in
both crystalline and non-crystalline solids. The movement or
displacement of such mobile defects is thermally activated, and thus
limited by the rate of atomic diffusion.
Hot metal work from a blacksmith.
Viscous flow near grain boundaries, for example, can give rise to
internal slip, creep and fatigue in metals. It can also contribute to
significant changes in the microstructure like grain growth and
localized densification due to the elimination of intergranular
porosity. Screw dislocations may slip in the direction of any lattice
plane containing the dislocation, while the principal driving force
for "dislocation climb" is the movement or diffusion of vacancies
through a crystal lattice.
In addition, the nondirectional nature of metallic bonding is also
thought to contribute significantly to the ductility of most metallic
solids. When the planes of an ionic bond slide past one another, the
resultant change in location shifts ions of the same charge into close
proximity, resulting in the cleavage of the crystal; such shift is not
observed in covalently bonded crystals where fracture and crystal
Main article: Alloy
An alloy is a mixture of two or more elements in which the main
component is a metal. Most pure metals are either too soft, brittle or
chemically reactive for practical use. Combining different ratios of
metals as alloys modifies the properties of pure metals to produce
desirable characteristics. The aim of making alloys is generally to
make them less brittle, harder, resistant to corrosion, or have a more
desirable color and luster. Of all the metallic alloys in use today,
the alloys of iron (steel, stainless steel, cast iron, tool steel,
alloy steel) make up the largest proportion both by quantity and
Iron alloyed with various proportions of carbon
gives low, mid and high carbon steels, with increasing carbon levels
reducing ductility and toughness. The addition of silicon will produce
cast irons, while the addition of chromium, nickel and molybdenum to
carbon steels (more than 10%) results in stainless steels.
Other significant metallic alloys are those of aluminium, titanium,
copper and magnesium.
Copper alloys have been known since
prehistory—bronze gave the
Bronze Age its name—and have many
applications today, most importantly in electrical wiring. The alloys
of the other three metals have been developed relatively recently; due
to their chemical reactivity they require electrolytic extraction
processes. The alloys of aluminium, titanium and magnesium are valued
for their high strength-to-weight ratios; magnesium can also provide
electromagnetic shielding. These materials are ideal
for situations where high strength-to-weight ratio is more important
than material cost, such as in aerospace and some automotive
Alloys specially designed for highly demanding applications, such as
jet engines, may contain more than ten elements.
Main article: Base metal
Zinc, a base metal, reacting with an acid
In chemistry, the term base metal is used informally to refer to a
metal that is easily oxidized or corroded, and reacts easily with
dilute hydrochloric acid (HCl) to form metal chloride and hydrogen.
Examples include iron, nickel, lead and zinc.
Copper is considered a
base metal as it is oxidized relatively easily, although it does not
react with HCl.
Base metal is commonly used in opposition to noble
In alchemy, a base metal was a common and inexpensive metal, as
opposed to precious metals, mainly gold and silver. A longtime goal of
the alchemists was the transmutation of base metals into precious
In numismatics, coins in the past derived their value primarily from
the precious metal content. Most modern currencies are fiat currency,
allowing the coins to be made of base metal.
Main article: Ferrous metallurgy
See also: Non-ferrous metals
The term "ferrous" is derived from the Latin word meaning "containing
iron". This can include pure iron, such as wrought iron, or an alloy
such as steel. Ferrous metals are often magnetic, but not exclusively.
Main article: Noble metal
Noble metals are metals that are resistant to corrosion or
oxidation, unlike most base metals. They tend to be precious
metals, often due to perceived rarity. Examples include gold,
platinum, silver, rhodium, iridium and palladium.
A gold nugget
Main article: Precious metal
A precious metal is a rare metallic chemical element of high economic
Chemically, the precious metals are less reactive than most elements,
have high luster and high electrical conductivity. Historically,
precious metals were important as currency, but are now regarded
mainly as investment and industrial commodities. Gold, silver,
platinum and palladium each have an
ISO 4217 currency code. The
best-known precious metals are gold and silver. While both have
industrial uses, they are better known for their uses in art, jewelry,
and coinage. Other precious metals include the platinum group metals:
ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which
platinum is the most widely traded.
The demand for precious metals is driven not only by their practical
use, but also by their role as investments and a store of value.
Palladium and platinum are, as of fall 2017, valued at about three
quarters the price of gold.
Silver is substantially less expensive
than these metals, but is often traditionally considered a precious
metal for its role in coinage and jewelry.
Main article: Heavy metals
A heavy metal is any relatively dense metal or metalloid. More
specific definitions have been proposed, but none have obtained
widespread acceptance. Some heavy metals have niche uses, or are
notably toxic; some are essential in trace amounts.
Main articles: Ore, Mining, and Extractive metallurgy
Metals are often extracted from the Earth by means of mining ores that
are rich sources of the requisite elements, such as bauxite.
located by prospecting techniques, followed by the exploration and
examination of deposits. Mineral sources are generally divided into
surface mines, which are mined by excavation using heavy equipment,
and subsurface mines.
Once the ore is mined, the metals must be extracted, usually by
chemical or electrolytic reduction.
Pyrometallurgy uses high
temperatures to convert ore into raw metals, while hydrometallurgy
employs aqueous chemistry for the same purpose. The methods used
depend on the metal and their contaminants.
When a metal ore is an ionic compound of that metal and a non-metal,
the ore must usually be smelted—heated with a reducing agent—to
extract the pure metal. Many common metals, such as iron, are smelted
using carbon as a reducing agent. Some metals, such as aluminium and
sodium, have no commercially practical reducing agent, and are
extracted using electrolysis instead.
Sulfide ores are not reduced directly to the metal but are roasted in
air to convert them to oxides.
Demand for metals is closely linked to economic growth. During the
20th century, the variety of metals uses in society grew rapidly.
Today, the development of major nations, such as China and India, and
advances in technologies, are fuelling ever more demand. The result is
that mining activities are expanding, and more and more of the world's
metal stocks are above ground in use, rather than below ground as
unused reserves. An example is the in-use stock of copper. Between
1932 and 1999, copper in use in the US rose from 73g to 238g per
Metals are inherently recyclable, so in principle, can be used over
and over again, minimizing these negative environmental impacts and
saving energy. For example, 95% of the energy used to make aluminium
from bauxite ore is saved by using recycled material. Levels of
metals recycling are generally low. In 2010, the International
Resource Panel, hosted by the United Nations Environment Programme
(UNEP) published reports on metal stocks that exist within society
and their recycling rates.
The report authors observed that the metal stocks in society can serve
as huge mines above ground. They warned that the recycling rates of
some rare metals used in applications such as mobile phones, battery
packs for hybrid cars and fuel cells are so low that unless future
end-of-life recycling rates are dramatically stepped up these critical
metals will become unavailable for use in modern technology.
Main article: Metallurgy
Metallurgy is a domain of materials science that studies the physical
and chemical behavior of metallic elements, their intermetallic
compounds, and their mixtures, which are called alloys.
Some metals and metal alloys possess high structural strength per unit
mass, making them useful materials for carrying large loads or
resisting impact damage.
Metal alloys can be engineered to have high
resistance to shear, torque and deformation. However the same metal
can also be vulnerable to fatigue damage through repeated use or from
sudden stress failure when a load capacity is exceeded. The strength
and resilience of metals has led to their frequent use in high-rise
building and bridge construction, as well as most vehicles, many
appliances, tools, pipes, non-illuminated signs and railroad tracks.
The two most commonly used structural metals, iron and aluminium, are
also the most abundant metals in the Earth's crust.
Metals are good conductors, making them valuable in electrical
appliances and for carrying an electric current over a distance with
little energy lost. Electrical power grids rely on metal cables to
distribute electricity. Home electrical systems, for the most part,
are wired with copper wire for its good conducting properties.
The thermal conductivity of metal is useful for containers to heat
materials over a flame.
Metal is also used for heat sinks to protect
sensitive equipment from overheating.
The high reflectivity of some metals is important in the construction
of mirrors, including precision astronomical instruments. This last
property can also make metallic jewelry aesthetically appealing.
Some metals have specialized uses; radioactive metals such as uranium
and plutonium are used in nuclear power plants to produce energy via
nuclear fission. Mercury is a liquid at room temperature and is used
in switches to complete a circuit when it flows over the switch
Shape memory alloy
Shape memory alloy is used for applications such as pipes,
fasteners and vascular stents.
Metals can be doped with foreign molecules—organic, inorganic,
biological and polymers. This doping entails the metal with new
properties that are induced by the guest molecules. Applications in
catalysis, medicine, electrochemical cells, corrosion and more have
World Bank reports that China was the top importer of ores and
metals in 2005 followed by the United States and Japan.
The nature of metals has fascinated humans for many centuries, because
these materials provided people with tools of unsurpassed properties
both in war and in their preparation and processing. Pure gold and
silver have been known to humans since the Stone Age.
Lead and silver
were fused from their ores as early as the fourth
Ancient Latin and Greek writers such as Theophrastus, Pliny the Elder
in his Natural History, or Pedanius Dioscorides, did not try to
classify metals. The ancient Europeans never attained the concept
"metal" as a distinct elementary substance with fixed, characteristic
chemical and physical properties. Following Empedocles, all substances
within the sublunary sphere were assumed to vary in their constituent
classical elements of earth, water, air and fire. Following the
Plato assumed that these elements could be further
reduced to plane geometrical shapes (triangles and squares) bounding
space and relating to the regular polyhedra in the sequence
earth:cube, water:icosahedron, air:octahedron, fire:tetrahedron.
However, this philosophical extension did not become as popular as the
simple four elements, after it was rejected by Aristotle. Aristotle
also rejected the atomic theory of Democritus, since he classified the
implied existence of a vacuum necessary for motion as a contradiction
(a vacuum implies nonexistence, therefore cannot exist). Aristotle
did, however, introduce underlying antagonistic qualities (or forces)
of dry vs. wet and cold vs. heat into the composition of each of the
four elements. The word "metal" originally meant "mines" and only
later gained the general meaning of products from materials obtained
in mines. In the first centuries A.D. a relation between the planets
and the existing metals was assumed as Gold:Sun, Silver:Moon,
Electrum:Jupiter, Iron:Mars, Copper:Venus, Tin:Mercury, Lead:Saturn.
After electrum was determined to be a combination of silver and gold,
the relations Tin:Jupiter and Mercury:Mercury were substituted into
the previous sequence.
Arabic and medieval alchemists believed that all metals, and in fact,
all sublunar matter, were composed of the principle of sulfur,
carrying the combustible property, and the principle of mercury, the
mother of all metals and carrier of the liquidity or fusibility, and
the volatility properties. These principles were not necessarily the
common substances sulfur and mercury found in most laboratories. This
theory reinforced the belief that the all metals were destined to
become gold in the bowels of the earth through the proper combinations
of heat, digestion, time, and elimination of contaminants, all of
which could be developed and hastened through the knowledge and
methods of alchemy.
Paracelsus added the third principle of salt,
carrying the nonvolatile and incombustible properties, in his tria
prima doctrine. These theories retained the four classical elements as
underlying the composition of sulfur, mercury and salt.
The first systematic text on the arts of mining and metallurgy was De
la Pirotechnia by Vannoccio Biringuccio, which treats the examination,
fusion, and working of metals. Sixteen years later, Georgius Agricola
De Re Metallica
De Re Metallica in 1555, a clear and complete account of the
profession of mining, metallurgy, and the accessory arts and sciences,
as well as qualifying as the greatest treatise on the chemical
industry through the sixteenth century. He gave the following
description of a metal in his
De Natura Fossilium
De Natura Fossilium (1546).
Metal is a mineral body, by nature either liquid or somewhat hard. The
latter may be melted by the heat of the fire, but when it has cooled
down again and lost all heat, it becomes hard again and resumes its
proper form. In this respect it differs from the stone which melts in
the fire, for although the latter regain its hardness, yet it loses
its pristine form and properties. Traditionally there are six
different kinds of metals, namely gold, silver, copper, iron, tin and
lead. There are really others, for quicksilver is a metal, although
the Alchemists disagree with us on this subject, and bismuth is also.
The ancient Greek writers seem to have been ignorant of bismuth,
wherefore Ammonius rightly states that there are many species of
metals, animals, and plants which are unknown to us.
smelted in the crucible and refined has as much right to be regarded
as a proper metal as is accorded to lead by writers. If when smelted,
a certain portion be added to tin, a bookseller's alloy is produced
from which the type is made that is used by those who print books on
paper. Each metal has its own form which it preserves when separated
from those metals which were mixed with it. Therefore neither electrum
nor Stannum [not meaning our tin] is of itself a real metal, but
rather an alloy of two metals.
Electrum is an alloy of gold and
silver, Stannum of lead and silver. And yet if silver be parted from
the electrum, then gold remains and not electrum; if silver be taken
away from Stannum, then lead remains and not Stannum. Whether brass,
however, is found as a native metal or not, cannot be ascertained with
any surety. We only know of the artificial brass, which consists of
copper tinted with the colour of the mineral calamine. And yet if any
should be dug up, it would be a proper metal. Black and white copper
seem to be different from the red kind. Metal, therefore, is by nature
either solid, as I have stated, or fluid, as in the unique case of
quicksilver. But enough now concerning the simple kinds.
ASM International (society)
Electric field screening
Properties of metals, metalloids and nonmetals
Properties and uses of metals
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De Re Metallica
De Re Metallica (1556) Tr. Herbert Clark Hoover
& Lou Henry Hoover (1912); Footnote quoting De Natura Fossilium
(1546), p. 180
Wikisource has the text of the 1879
American Cyclopædia article
The dictionary definition of metal at Wiktionary
Media related to Metals at Wikimedia Commons
Metal at Encyclopædia Britannica
18-column, large cells
32-column, large cells
Janet's left step table
Extension beyond the 7th period
1 (Alkali metals)
Alkaline earth metals)
18 (Noble gases)
Alkaline earth metals
Lists of metalloids by source
Platinum-group metals (PGM)
By: Abundance (in humans)
Heat of fusion
Heat of vaporization
Speed of sound
Thermal expansion coefficient
in East Asia
systematic element name
Periodic table (Large cells)
Alkaline earth metal
BNF: cb11935875s (data)