Metals

from Wikipedia, the free encyclopedia

Metals (from ancient Greek μέταλλον metallon "mine, ore, metal") are the chemical elements that are to the left and below a dividing line from boron to astatine in the periodic table of the elements . That is about 80 percent of the chemical elements, whereby the transition to the non-metals via the semimetals is fluid and many of them can form modifications with metallic and atomic bonds.

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

  1. high electrical conductivity , which decreases with increasing temperature,
  2. high thermal conductivity ,
  3. Ductility (deformability)
  4. metallic sheen (mirror finish).

All of these properties are based on the fact that the atoms in question are held together by the metallic bond , the most important feature of which is the freely moving electrons in the lattice.

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

At extremely rapid cooling, atoms of these elements can also cluster amorphously without forming a crystal lattice - see metallic glass .

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

Metals have found diverse uses as materials since the beginning of civilization . Under the term metal physics or metal science, physicists and materials scientists deal with all the basics, see under solid state physics , and with applications, see under materials science .

Classification

The elements, divided into non-metals, semi-metals and metals. The latter differentiated according to density (calculated for Fm to Og)
non-metal: up to 5 g / cm³
(semi) metal: up to 5 g / cm³ from 5 g / cm³   from 10 g / cm³   from 20 g / cm³
H Hey
Li Be B. C. N O F. No
N / A Mg Al Si P S. Cl Ar
K Approx Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mon Tc Ru Rh Pd Ag CD In Sn Sb Te I. Xe
Cs Ba La * Hf Ta W. re Os Ir Pt Au Ed Tl Pb Bi Po At Marg
Fr. Ra Ac ** Rf Db Sg Bra Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Above
 
  * Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho He Tm Yb Lu
  ** Th Pa U Np Pooh At the Cm Bk Cf It Fm Md No Lr

Traditionally, metals are divided into heavy metals and light metals according to their density and into noble metals and base metals according to their reactivity , the latter being 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 on the left and below a line from boron to astatine in the periodic table of elements , with the metallic character increasing from top to bottom or from right to left. At the very top right are the non-metals , with the semi- metals in between . The subgroup elements are all metals. The border to the non-metallic is fluid. For example, antimony , arsenic , cerium, and tin have both metallic and non-metallic modifications .

Belonging to main or subgroups of the periodic table is also decisive for chemical behavior.

Physical Properties

General

A piece of high purity iron with a purity of 99.97%
Body-centered cubic unit cell of an iron crystal

The following properties of atoms are required for the formation of the metallic state:

The result is that such atoms cannot connect to one another via atomic bonds to form molecules or lattices. At most, atomic bonds occur in metal vapors, e.g. B. sodium vapor consists of about 1% Na 2 molecules.

Rather, metal atoms organize themselves into a metal lattice , which consists of positively charged atomic cores , while the valence electrons are distributed over the entire lattice; none of these electrons belong to any particular nucleus. These freely moving electrons can be imagined as particles of a gas that fills the space between the atomic cores. Since this electron gas is responsible for the good electrical conductivity of the metals, the energy level at which the free electrons are located is called the “ conduction band ”. The precise energetic conditions are described by the band model based on the orbital model .

The following typical properties of metals result from this type of bond and this lattice structure :

  • Shine (mirror shine ): The freely moving electrons can re-emit almost all of the incident electromagnetic radiation up to wavelengths of the X-ray radiation; this is how the shine and reflection arise ; That is why mirrors are made from smooth metal surfaces .
  • Opacity: The above-described reflection taking place on the metal surface and the absorption of the non-reflected portion mean that, for example, light can hardly enter metal. Metals are therefore only slightly translucent in the thinnest layers and appear gray or blue when viewed through.
  • Good electrical conductivity : the migration of the freely moving electrons in one direction is the electrical current .
  • Good thermal conductivity : The easily displaceable electrons take part in the movement of heat. They also transfer the intrinsic thermal movement of the atomic cores (vibrations) and thus contribute to heat transport, cf. Conduction .
  • Good deformability ( ductility ): There are grain boundaries and dislocations in the metal , which can move even when stretched below the elongation at break , that is, without losing cohesion; Depending on the type of grid, a metal deforms before it breaks.
  • Relatively high melting point : It results from the all-round binding forces between the cations and the freely moving electrons, but an effect that is less strong than the electrostatic forces of attraction between ions in salt crystals.

Melting and boiling temperatures

As high-melting is referred to metals whose melting point T E above 2000 K or above the melting point of platinum (T E -platinum = 2045 K = 1772 ° C). These include the precious 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 conductivity properties

The properties that are relevant for heat conduction, such as density , heat capacity , thermal conductivity and thermal diffusivity, vary greatly. Silver, for example, has a thermal conductivity of 427 W / (m · K) which is around 50 times higher than that of manganese, see list of values .

Physical properties of some metals. The highest and lowest values ​​are marked in color.
element lithium aluminum chrome iron copper zinc silver tin Cesium tungsten osmium gold mercury lead
Melting point in ° C (1013 hPa) 180.54 660.2 1907 1538 1084.62 419.53 961.78 231.93 28.44 3422 3130 1064.18 −38.83 327.43
Boiling point in ° C (1013 hPa) 1330 2470 2482 3000 2595 907 2210 2602 690 5930 5000 2970 357 1744
Density in g / cm 3 (20 ° C, 1013 hPa) 0.534 2.6989 7.14 7,874 8.92 7.14 10.49 α-tin: 5.769

β-tin: 7.265

1.90 19.25 22.59 19.32 13.5459 11,342
Mohs hardness 0.6 2.75 8.5 4.0 3.0 2.5 2.5 1.5 0.2 7.5 7.0 2.5 1.5
Electrical conductivity in 10 6 S / m 10.6 37.7 7.87 10.0 58.1 16.7 61.35 8.69 4.76 18.52 10.9 45.5 1.04 4.76
Thermal conductivity in W / ( m · K ) 85 235 94 80 400 120 430 67 36 170 88 320 8.3 35
Atomic number 3 13 24 26th 29 30th 47 50 55 74 76 79 80 82
Atomic mass in u 6.94 26,982 51,996 55.845 63,546 65.38 107.868 118.710 132.905 183.84 190.23 196.967 200.592 207.2
Electronegativity 0.98 1.61 1.66 1.83 1.9 1.65 1.93 1.96 0.79 2.36 2.2 2.54 2.0 2.33
Crystal system (1) cl cl cl cl cF hcp cF α-tin: A4

β-tin: tl

cl cl hcp cF P 3 cF

Chemical properties

When associated with non-metals, the metals generally appear as cations ; That is, the outer electrons are completely given up to the non-metal atoms and an ionic compound ( salt ) is formed. In an ion lattice , the ions are only held together by electrostatic forces .

In compounds with transition metals and in the case of larger anions (such as the sulfide ion ), all transition stages to the atomic bond can occur.

With non-metals such as hydrogen , carbon and nitrogen also are intercalation compounds are formed, wherein the non-metallic atoms are located in gaps of the metal grid, without substantially altering it. These intercalation compounds retain the typical metal properties such as electrical conductivity .

Metal cations, v. a. those of the subgroup metals form complex compounds with bases ( water , ammonia , halides , cyanides, etc.) , the stability of which cannot be explained by electrostatic attraction alone.

Metals in higher oxidation states also form complex anions, e.g. B .:

Chromium trioxide dissolves in potassium hydroxide to form potassium chromate and water.

Alloys

Mixtures of a metal and one or more other elements, which can be metallic or non-metallic, are called alloys if this mixture has the typical metallic properties (ductility, electrical conductivity, ...), i.e. if there is still a metallic bond.

Alloys often have completely different physical and chemical properties than pure metals. In particular, the hardness and strength are sometimes orders of magnitude higher. The corrosion resistance can also increase significantly. The melting point of alloys, on the other hand, is often below that of pure metals; with a certain composition the lowest melting point is reached, the eutectic .

As the first specifically manufactured alloy in human history, bronze was used, an alloy predominantly made of copper and 5 to 20% tin. Today, steel is the most frequently used alloy, a mixture of iron with shares of carbon and some other elements.

Occurrence

The core of the earth consists mainly of iron , because it occurs in very large quantities firstly because it is the most stable element in terms of nuclear physics , and secondly because of its high density.

In the earth's crust, on the other hand, non-metals predominate; relatively common metals are aluminum , iron , manganese , titanium , calcium , magnesium , sodium and potassium . Many rare metals, however, occur in their mining sites in a highly enriched manner. Rocks that contain usable metals in minable concentrations are called ores . The most important ores include:

The metals are metallurgically extracted from the respective ores .

Some precious metals, v. a. Gold , also come dignified , i.e. H. in pure form and not as a compound (ore or mineral ).

use

"Eichbaum" silver coin
five Reichsmarks (1927–1933)
Copper roof in Dresden
Prices for metals

Many metals are important materials. The modern world would be impossible without metals. It is not without reason that phases of human development are referred to as the Stone Age , Bronze Age and Iron Age according to the materials used .

Pure metals are used to manufacture electrical cables because they have the greatest conductivity. Mainly unalloyed copper and aluminum and rarely gold are used for this. Otherwise pure metals are practically never used.

The following list contains the most important metals and alloy components , not compounds:

Metal in astrophysics

In astrophysics , metal is defined differently, see metallicity ; here it describes every chemical element above a certain atomic number (usually higher than helium ). These are all elements created by nuclear fusion in stars or by supernovae , whereas hydrogen and helium (together with some traces of lithium ) are thought to have been created by the big bang . The metallicity of a star is related to the time it was formed (see population ).

It is assumed that hydrogen in the interior of sufficiently heavy gas planets can change into the metallic state (in the sense of the chemical metal definition); this metallic hydrogen is probably also responsible for the extremely strong magnetic field of Jupiter . However, metallic hydrogen does not contribute to the astrophysical metallicity of the object in which it occurs.

Metal in Chinese Philosophy

Metal here denotes an element of the traditional five-element theory .

heraldry

As metals in the be Heraldry the tinctures (Coat of Arms colors) Gold and silver respectively. In the case of heraldic paintings, the color yellow is used as a substitute for gold and the color white as a substitute for silver .

See also

literature

On the history of metals
  • Karl Otto Henseling : bronze, iron, steel. Significance of metals in history (= Rororo. Rororo-Sachbuch 7706 = cultural history of natural sciences and technology. Vol. 6). Rowohlt, Reinbek near Hamburg 1981, ISBN 3-499-17706-4 .
  • Franz Zippe : History of Metals. Vienna 1857; Reprint Wiesbaden 1967.
  • Adelbert Rössing: History of Metals. Berlin 1901.
To the metals
  • Erhard Hornbogen, Hans Warlimont: Metals - Structure and Properties of Metals and Alloys , Springer, 6th edition, 2016, ISBN 978-3-662-47952-0 .
  • Wolfgang Glöckner, Walter Jansen, Rudolf Georg Weissenhorn (eds.): Handbook of experimental chemistry. Upper secondary level. Volume 5: Chemistry of utility metals. Aulis-Verlag Deubner, Cologne 2003, ISBN 3-7614-2384-5 .

Web links

Wiktionary: Metal  - explanations of meanings, word origins, synonyms, translations
Commons : Metals  - collection of images, videos and audio files

Individual evidence

  1. ↑ Uwe Kreibig: When is gold a metal? In: Physik-Journal . Vol. 1, No. 1, 2002, ISSN  1617-9439 , pp. 20-21, online (PDF; 461 kB) .
  2. ↑ Burkhard Fricke (1975), Superheavy elements: a prediction of their chemical and physical properties
  3. ↑ Römpp Lexikon Chemie , 9th edition, Volume 4, page 2709
  4. ↑ a b c P. Häussinger, R. Glatthaar, W. Rhode, H. Kick, C. Benkmann, J. Weber, H.-J. Wunschel, V. Stenke, E. Leicht, H. Stenger: Noble Gases. In: Ullmann's Encyclopedia of Industrial Chemistry . Wiley-VCH, Weinheim 2006 ( doi : 10.1002 / 14356007.a17_485 ).