Metal

Gold Nugget

Copper disc produced by the continuous casting process, etched, diam. about 100 mm, purity ≥ 99.95%.

Metals (from the Greek μέταλλον Metallon ) form those chemical elements that are located in the periodic table of elements to the left and below a line of separation of boron to astatine. That is about 80 percent of the chemical elements, the transition to the non-metals on the semimetals is fluid and can make many modifications thereof with metallic and atomic bonding.

The term is also used for some alloys and intermetallic phases; it applies to all materials which, in solid or liquid form, the following four characteristic metallic material properties:

All these properties are due to the fact that the cohesion of the relevant atoms takes place with the metallic bond, whose main feature is the free electrons in the lattice.

A single atom of these elements has no metallic properties; it is not a metal. Only if several such atoms interact with each other and there is a metallic bond between them, show such atomic groups ( clusters) metallic properties.

Atoms of these elements can assemble also amorphous at extremely rapid cooling without forming a crystal lattice - see metallic glass.

On the other hand, atoms of other elements can under extreme conditions (pressure ) enter into metallic bonds and thus assume the metallic properties mentioned - see metallic hydrogen.

Metals found since the beginning of civilization diverse applications as materials. The term metal physics or metallurgy physicists and materials scientists deal with all the basics, see solid-state physics, and applications, refer to materials science.

Classification

Traditionally, one divides metals according to the density in heavy metals and light metals and the reactivity in precious metals and base metals, the latter are good reducing agents. See also the main article metallic material (as well as the reactivity under redox reaction ).

Metals are formed from the elements that are in the periodic table of elements in the area to the left and below a line from boron to astatine, the metallic character from top to bottom and increases from right to left. At the top right are the non-metals, in between the semi-metals. The transition group elements form invariably metals.

The chemical behavior of the membership of the main or secondary groups of the periodic system is critical.

Physical Properties

General

Prerequisite for the formation of the metallic state, the following properties of atoms:

• The number of electrons in the outer shell is low and less than the coordination number
• The ( for the removal of these outer electrons necessary ) ionization energy is small ( < 10 eV )

As a result, these atoms with each other can not connect using atomic bonds to form molecules or lattices. At most, in metal vapors occur atomic bonds, such as sodium vapor is about 1% of Na2 molecules.

Such atoms arrange themselves rather to a metal grid, which consists of positively charged atomic cores, while the valence electrons are distributed over the entire grid; none of these electrons is one more on a specific core. These free electrons can be thought of as particles of a gas that fills the space between the atomic cores. Since this electron gas causes the good electrical conductivity of metals, among other things, the energy level at which there are free electrons, called the " conduction band ". The exact energy situation describes the band model based on the orbital model.

From this weave and this lattice structure following typical properties of metals results in:

• Gloss ( mirror finish ): The free-moving electrons can emit up to wavelengths of X-rays again almost all incident electromagnetic radiation; so the shine and reflection arise; therefore mirrors are made ​​of smooth metal surfaces.
• Opacity: The above-described, takes place at the metal surface reflection and the absorption of the non-reflected proportion cause, for example, the light can hardly occur in the metal. Metals are therefore somewhat translucent only in the thinnest layers and appear gray or blue in transmitted light.
• Good electrical conductivity: The walk to the free electrons in one direction is the electric current.
• Good thermal conductivity: the easily movable electrons take part in the movement of heat. They also transmit the inherent thermal motion of the ions ( vibrations ) and thus contribute to the heat transport, cf heat conduction.
• Good deformability (ductility ): In metal there are grain boundaries and dislocations, which can move even at a strain below the breaking strain, that is, is lost without the cohesion; depending on the lattice type so deforms a metal before it breaks.
• A relatively high melting point: It results from the omni-directional bond strength between the cations and the free electrons, a strong effect, however, less than the electrostatic attraction forces between the ions in salt crystals.

Melting and boiling points

As a high melting point is referred to as metal whose melting point TE 2000 K or above the melting point of platinum ( platinum TE = 2045 K = 1772 ° C). These include the noble metals ruthenium, rhodium, osmium and iridium, and metals of Groups IVB ( zirconium, hafnium), VB (vanadium, niobium, tantalum), VIB ( chromium, molybdenum, tungsten ), and VIIB ( technetium, rhenium ).

Thermal conduction

Relevant for the thermal conduction properties such as density, heat capacity, thermal conductivity and thermal conductivity vary greatly. Such as silver with 427 W / ( m · K) was about 50 times higher thermal conductivity than manganese, see list of values.

Chemical Properties

In conjunction with non-metals, the metals generally act as cations, i.e., the outer electrons are completely discharged to the non-metal atoms and an ionic compound is formed ( salt). In an ionic lattice, the ions are held together by electrostatic forces.

For compounds with transition metals and with larger anions ( such as the sulfide ion ), all transitional stages occur for atomic bond.

With non-metals such as hydrogen, carbon, and nitrogen also intercalation compounds are formed, wherein the non-metal atoms are gaps in the metal lattice without changing this much. These intercalation compounds retain the typical metal properties such as electrical conductivity.

Metal cations, v. a to the subgroup metals, forming with bases ( water, ammonia, halides, cyanides and v. a ) complex compounds whose stability can not be explained solely by the electrostatic attraction.

Metals in higher oxidation states also form complex anions, for example:

Alloys

The compounds or solutions of different metals together or reciprocally hot alloys. These often have very different physical and chemical properties than the pure metals. In particular, the hardness is shown to be higher by orders of magnitude. The corrosion resistance can also increase significantly. The melting point of alloys, however, is often below that of the pure metals; for a given composition of the lowest melting point is reached, the eutectic.

As the first - specifically produced - alloy of human history, the tin bronze was used, which represented something of a " wave of innovation " in the Bronze Age. Today, the steel represents the alloy most commonly used

Occurrence

The Earth's core consists mainly of iron, since it is found firstly in very large quantities, because it is the core physically stable element, and secondly because of its high density.

In the earth, however, outweigh the non-metals, relatively common metals are aluminum, iron, manganese, titanium, calcium, magnesium, sodium and potassium. Many rare metals occur but in their mining sites on highly enriched. Rocks which contain useful metals in mineable concentrations are called ores. Among the most important ores include:

• Oxides
• Sulfides
• Carbonates

Other compounds such as sodium chloride or lime however, are not referred to as ores.

Some precious metals, v. a gold, are also solid, that is, in pure form and not as the compound ( ore or mineral ) ago.

Use

Many metals are important materials. The modern world would be impossible without metals. Not without reason are called phases of human development according to the materials used, as Stone Age, Bronze Age, Iron Age.

Pure metals are used for the production of electrical cables, since they have the greatest conductivity. This is mainly due unalloyed copper and aluminum and rarely, gold is used. Otherwise, pure metals are hardly ever used.

The following list contains the most important metals and alloy components, no connections:

• Aluminium most important light metal
• Beryllium alloys, particularly copper and aluminum; Nuclear weapons ( neutron reflector )
• Bismuth and alloys
• Cadmium: part of accumulators
• Chromium: alloying component (Chromium - vanadium steel, chrome - nickel - steel, chrome - molybdenum steel), metal coating
• Iron: the most important metal material (steel, cast iron), many alloys
• Gallium thermometer
• Gold: jewelry metal, gold leaf, electrical engineering, value system, currency hedging
• Iridium: electrodes, spark plugs
• Potassium: alloys with sodium as a coolant in nuclear reactors
• Cobalt: Magnets
• Copper: Electrical Engineering ( second highest conductivity after silver), bronze, brass
• Magnesium: for very lightweight workpieces; Disposable flash bulbs or flash powder
• Manganese alloy component (manganese steel)
• Molybdenum alloy component ( molybdenum steel ) to increase the hot strength
• Sodium alloyed with potassium as the coolant in nuclear reactors
• Nickel alloys ( nickel-iron, nickel-chromium, nickel - copper, etc. ), an alloying constituent (chrome -nickel steel ), magnets,
• Osmium earlier in bulbs
• Palladium: catalysis, hydrogen storage
• Platinum: jewelry metal catalysis, one of the most precious metals
• Mercury: thermometer, energy saving lamps
• Rhodium: Jewelry Metal
• Of ruthenium catalyst, increase the hardness of platinum and palladium
• Silver: jewelry metal, Photography
• Tantalum: Capacitors
• Titanium for lightweight construction without regard to the cost, jewelry
• Uranium: Nuclear reactors, radioactivity, Stories
• Vanadium alloy component (chrome - vanadium - steel) for heat- resistant steels, catalyst for the synthesis of sulfuric acid ( vanadium (V ) oxide)
• Tungsten filament lamps (highest melting point of all metals), special steels, pen refills (balls)
• Zinc alloy component (brass), zinc die castings ( zamak ), zinc coating of steel parts ( hot-dip galvanizing, continuous strip galvanizing )
• Tin alloy component ( Bronze), Lote ( solder), tinplate, tin figures
• Zirconium: Case for fuel rods in nuclear power plants

Metal in astrophysics

In astrophysics of stars and galaxies metal is defined differently, see metallicity; here it refers to any chemical element above a certain atomic number ( usually higher than helium). These are all elements created by nuclear fusion in stars or supernovae, whereas hydrogen and helium (along with some traces of lithium) thought of as created by the Big Bang. The metallicity of objects in space can therefore be regarded as an indicator of their respective stellar activity.

It is believed that hydrogen can go inside of sufficiently heavy gas planet in the metallic state (in terms of chemical metal definition); this metallic hydrogen is probably also responsible for the extremely strong magnetic field of Jupiter. But metallic hydrogen does not contribute to astrophysical metallicity of the object in which it occurs.

Metal in the Chinese philosophy

Metal referred to herein, an element of the traditional five - element theory.

Heraldry

As metals tinctures (Coat colors) are referred to gold and silver in heraldry. With coat of arms paintings the color yellow and silver as a substitute for the color white is used as a substitute for gold.