Editing Metal (section)

==Properties==

===Form and structure===
[[File:Gallium crystals.jpg|thumb|[[Gallium]] crystals|alt=Gallium crystals on a table]]
Most metals are shiny and [[lustrous]], at least when polished, or fractured. Sheets of metal thicker than a few [[micrometre]]s appear opaque, but [[gold leaf]] transmits green light. This is due to the freely moving electrons which reflect light.<ref name="Kittel-2018" /><ref name="Ashcroft-1976" />

Although most elemental metals have higher [[density|densities]] than [[nonmetal]]s,<ref name="morty">{{cite book |author=Mortimer, Charles E. |title=Chemistry: A Conceptual Approach |location=New York |publisher=D. Van Nostrad Company |edition=3rd |year=1975}}</ref> there is a wide variation in their densities, [[lithium]] being the least dense (0.534&nbsp;g/cm<sup>3</sup>) and [[osmium]] (22.59&nbsp;g/cm<sup>3</sup>) the most dense. Some of the [[Superheavy element|6d transition metals]] are expected to be denser than osmium, but their known isotopes are too unstable for bulk production to be possible<ref>{{Cite conference|last1=Moller|first1=P.|last2=Nix|first2=J. R.|date=1994|title=Fission properties of the heaviest elements|url=https://digital.library.unt.edu/ark:/67531/metadc674703/m2/1/high_res_d/32502.pdf|conference=Dai 2 Kai Hadoron Tataikei no Simulation Symposium, Tokai-mura, Ibaraki, Japan|publisher=[[University of North Texas]]|access-date=2020-02-16}}</ref> Magnesium, aluminium and titanium are [[light metal]]s of significant commercial importance. Their respective densities of 1.7, 2.7, and 4.5&nbsp;g/cm<sup>3</sup> can be compared to those of the older structural metals, like iron at 7.9 and copper at 8.9&nbsp;g/cm<sup>3</sup>. The most common lightweight metals are [[Aluminium alloy|aluminium]]<ref>{{Citation |last=Benedyk |first=J. C. |title=3 - Aluminum alloys for lightweight automotive structures |date=2010-01-01 |work=Materials, Design and Manufacturing for Lightweight Vehicles |pages=79–113 |editor-last=Mallick |editor-first=P. K. |url=https://www.sciencedirect.com/science/article/pii/B9781845694630500031 |access-date=2024-07-23 |series=Woodhead Publishing Series in Composites Science and Engineering |publisher=Woodhead Publishing |doi=10.1533/9781845697822.1.79 |isbn=978-1-84569-463-0|url-access=subscription }}</ref><ref>{{Cite journal |last1=Li |first1=Shuang–Shuang |last2=Yue |first2=Xin |last3=Li |first3=Qing–Yuan |last4=Peng |first4=He–Li |last5=Dong |first5=Bai–Xin |last6=Liu |first6=Tian–Shu |last7=Yang |first7=Hong–Yu |last8=Fan |first8=Jun |last9=Shu |first9=Shi–Li |last10=Qiu |first10=Feng |last11=Jiang |first11=Qi–Chuan |date=2023-11-01 |title=Development and applications of aluminum alloys for aerospace industry |journal=Journal of Materials Research and Technology |volume=27 |pages=944–983 |doi=10.1016/j.jmrt.2023.09.274 |issn=2238-7854|doi-access=free }}</ref> and [[Magnesium alloy|magnesium]]<ref>{{Cite journal |last1=Gupta |first1=M. |last2=Wong |first2=W. L. E. |date=2015-07-01 |title=Magnesium-based nanocomposites: Lightweight materials of the future |url=https://www.sciencedirect.com/science/article/pii/S104458031500131X |journal=Materials Characterization |volume=105 |pages=30–46 |doi=10.1016/j.matchar.2015.04.015 |issn=1044-5803|url-access=subscription }}</ref><ref>{{Cite journal |last1=Ogawa |first1=Yukiko |last2=Ando |first2=Daisuke |last3=Sutou |first3=Yuji |last4=Koike |first4=Junichi |date=2016-07-22 |title=A lightweight shape-memory magnesium alloy |url=https://www.science.org/doi/10.1126/science.aaf6524 |journal=Science |language=en |volume=353 |issue=6297 |pages=368–370 |doi=10.1126/science.aaf6524 |pmid=27463668 |bibcode=2016Sci...353..368O |issn=0036-8075|url-access=subscription }}</ref> alloys.

[[File:Ductility.svg|thumb|right|Schematic appearance of round metal bars after tensile testing.<br />
(a) Brittle fracture<br />
(b) Ductile fracture<br />
(c) Completely ductile fracture]]

Metals are typically malleable and ductile, deforming under stress without [[cleavage (crystal)|cleaving]].<ref name="morty"/> The nondirectional nature of metallic bonding contributes to the ductility of most metallic solids, where the [[Peierls stress]] is relatively low allowing for [[dislocation]] motion, and there are also many combinations of planes and directions for [[Plastic Deformation|plastic deformation]].<ref name="Weertman-1992">{{Cite book |last1=Weertman |first1=Johannes |title=Elementary dislocation theory |last2=Weertman |first2=Julia R. |date=1992 |publisher=Oxford University Press |isbn=978-0-19-506900-6 |location=New York}}</ref> Due to their having close packed arrangements of atoms the [[Burgers vector]] of the dislocations are fairly small, which also means that the energy needed to produce one is small.<ref name="Callister-1997" /><ref name="Weertman-1992" /> In contrast, in an ionic compound like table salt, the Burgers vectors are much larger and the energy to move a dislocation is far higher.<ref name="Callister-1997" /> Reversible [[deformation (engineering)|elastic deformation]] in metals can be described well by [[Hooke's law]] for the restoring forces, where the [[stress (mechanics)|stress]] is linearly proportional to the [[deformation (mechanics)|strain]].<ref>{{Cite book |last=Timoshenko |first=Stephen |url=https://books.google.com/books?id=tkScQmyhsb8C&dq=introduction+to+elasticity+timoshenko&pg=PA7 |title=History of Strength of Materials: With a Brief Account of the History of Theory of Elasticity and Theory of Structures |date=1983-01-01 |publisher=Courier Corporation |isbn=978-0-486-61187-7 |language=en}}</ref>

A temperature change may lead to the movement of [[crystallographic defect|structural defects]] in the metal such as [[grain boundaries]], [[vacancy defect|point vacancies]], [[dislocations|line and screw dislocations]], [[stacking fault]]s and [[crystal twinning|twins]] in both [[crystalline]] and [[amorphous solid|non-crystalline]] metals. Internal [[slip (materials science)|slip]], [[creep (deformation)|creep]], and [[fatigue (material)|metal fatigue]] may also ensue.<ref name="Callister-1997" /><ref name="Weertman-1992" />

The atoms of simple metallic substances are often in one of three common [[crystal structure]]s, 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.<ref>{{cite book |last1=Holleman |first1=A. F. |last2=Wiberg |first2=E. |title=Inorganic Chemistry |publisher=Academic Press |location=San Diego |year=2001 |isbn=0-12-352651-5}}</ref>
<gallery widths="135" heights="135">
File:Cubic-body-centered.svg|Body-centered cubic crystal structure, with a 2-atom unit cell, as found in e.g. chromium, iron, and tungsten
File:Cubic-face-centered.svg|Face-centered cubic crystal structure, with a 4-atom unit cell, as found in e.g. aluminium, copper, and gold
File:Hexagonal close packed.svg|Hexagonal close-packed crystal structure, with a 6-atom unit cell, as found in e.g. titanium, cobalt, and zinc
File:PSM V87 D113 Arrangement of atoms in a rock salt crystal.png|Arrangement of atoms in a rock salt crystal such as TiN
</gallery>

Many other metals with different elements have more complicated structures, such as [[rock-salt structure]] in [[titanium nitride]] or [[perovskite (structure)]] in some nickelates.<ref>{{Cite book |last=Koster |first=G. |title=Epitaxial growth of complex metal oxides |date=2015 |publisher=Elsevier |isbn=978-1-78242-245-7 |location=Boston, MA}}</ref>

===Electrical and thermal===
[[File:Band filling diagram.svg|thumb|{{{1|right}}}|300px|

The energy states available to electrons in different kinds of solids at [[thermodynamic equilibrium]].
<div style="height:5px;font-size:1px;">&nbsp;</div>
Here, height is energy while width is the [[density of states|density of available states]] for a certain energy in the material listed. The shading follows the [[Fermi–Dirac statistics|Fermi–Dirac distribution]] ('''black'''=all states filled, '''white'''=no state filled).
<div style="height:5px;font-size:1px;">&nbsp;</div>
The [[Fermi level]] ''E''<sub>F</sub> is the energy level at which the electrons are in a position to interact with energy levels above them. In metals and [[semimetal]]s the [[Fermi level]] ''E''<sub>F</sub> lies inside at least one band of energy states.
<div style="height:6px;font-size:1px;">&nbsp;</div>
In [[insulator (electricity)|insulators]] and [[semiconductor]]s the Fermi level is inside a [[band gap]]; however, in semiconductors the bands are near enough to the Fermi level to be [[Fermi–Dirac statistics|thermally populated]] with electrons or [[electron hole|holes]].
]]

The electronic structure of metals makes them good [[electrical conductivity|conductors of electricity]]. In general, electrons in a material all have different [[Momentum|momenta]], which average to zero when there is no external [[voltage]]. In metals, when a voltage is applied, some electrons shift to states with slightly higher momentum in the direction of the electric field, while others slow down slightly. This creates a net [[drift velocity]] that leads to an electric current.<ref name="Kittel-2018" /><ref name="Ashcroft-1976" /><ref name="h887">{{cite book |last=Simon |first=Steven H. |title=The Oxford Solid State Basics |date=2013-06-21 |publisher=OUP Oxford |isbn=978-0-19-150210-1 |publication-place=Oxford |pages=173-174}}</ref> This involves small changes in which [[Quantum state|wavefunctions]] the electrons are in, changing to those with the higher momenta. According to the [[Pauli exclusion principle]], no two electrons can occupy the same quantum state.<ref>{{Cite book |last=Schiff |first=Leonard |author-link=Leonard I. Schiff |url=https://ia601609.us.archive.org/11/items/ost-physics-schiff-quantummechanics/Schiff-QuantumMechanics.pdf |title=Quantum Mechanics |publisher=[[McGraw-Hill]] |year=1959}}</ref> Therefore, for the electrons to shift to higher-momentum states, such states must be unoccupied. In metals, these empty [[Delocalized electron|delocalized electron states]] are available at energies near the highest occupied levels, as shown in the Figure.

By contrast, semiconductors like silicon and nonmetals like [[strontium titanate]] have an [[Band gap|energy gap]] between the highest filled electron states (the valence band) and the lowest empty states (the conduction band). A small electric field is insufficient to excite electrons across this gap, making these materials poor electrical conductors.<ref name="h887" /> However, semiconductors can carry some current when [[Doping (semiconductor)|doped]] with elements that introduce additional partially occupied energy states, or when thermal excitation enables electrons to cross the energy gap.<ref name="Solymar-2004">{{Cite book |last1=Solymar |first1=L. |title=Electrical properties of materials |last2=Walsh |first2=D. |date=2004 |publisher=Oxford University Press |isbn=978-0-19-926793-4 |edition=7th |location=Oxford; New York}}</ref>

The elemental metals have electrical conductivity values of from 6.9 × 10<sup>3</sup> [[Siemens (unit)|S]]/cm for [[manganese]] to 6.3 × 10<sup>5</sup> S/cm for [[silver]]. In contrast, a [[semiconductor|semiconducting]] metalloid such as [[boron]] has an electrical conductivity 1.5 × 10<sup>−6</sup> S/cm. Typically, the electrical conductivity of metals decreases with heating because the increased thermal motion of the atoms makes it harder for electrons to flow.<ref>{{Cite book |title=Springer Handbook of Electronic and Photonic Materials |date=2017 |publisher=Springer International Publishing : Imprint: Springer |isbn=978-3-319-48933-9 |editor-last=Capper |editor-first=Peter |edition=2nd ed. 2017 |series=Springer Handbooks |location=Cham |pages=23 |editor-last2=Kasap |editor-first2=Safa}}</ref> Exceptionally, [[plutonium]]'s electrical conductivity increases when heated in the temperature range of around −175 to +125&nbsp;°C, with anomalously large thermal expansion coefficient and a phase change from monoclinic to face-centered cubic near 100&nbsp;°C.<ref name="HeckerPlutonium">{{Cite journal |last=Hecker |first=Siegfried S. |date=2000 |title=Plutonium and its alloys: from atoms to microstructure |url=https://fas.org/sgp/othergov/doe/lanl/pubs/00818035.pdf |url-status=live |journal=Los Alamos Science |volume=26 |pages=290–335 |archive-url=https://web.archive.org/web/20090224204042/http://www.fas.org/sgp/othergov/doe/lanl/pubs/00818035.pdf |archive-date=February 24, 2009 |access-date=February 15, 2009}}</ref> This behavior, along with similar phenomena observed in other transuranic elements, is attributed to more complex relativistic and spin interactions which are not captured in simple models.<ref>{{Cite journal |last1=Tsiovkin |first1=Yu. Yu. |last2=Lukoyanov |first2=A. V. |last3=Shorikov |first3=A. O. |last4=Tsiovkina |first4=L. Yu. |last5=Dyachenko |first5=A. A. |last6=Bystrushkin |first6=V. B. |last7=Korotin |first7=M. A. |last8=Anisimov |first8=V. I. |last9=Dremov |first9=V. V. |date=2011 |title=Electrical resistivity of pure transuranium metals under pressure |url=https://linkinghub.elsevier.com/retrieve/pii/S0022311511003369 |journal=Journal of Nuclear Materials |volume=413 |issue=1 |pages=41–46 |doi=10.1016/j.jnucmat.2011.03.053 |bibcode=2011JNuM..413...41T |issn=0022-3115|url-access=subscription }}</ref>
[[File:TiN_DOS.tif|thumb|Density of states of TiN, with the occupied states shaded in blue and the Fermi level at the x origin. All the states, as well as those associated with the Ti and N atoms are shown.|left|250x250px]]
All of the metallic alloys as well as conducting ceramics and polymers are metals by the same definition; for instance [[titanium nitride]] has delocalized states at the Fermi level. They have electrical conductivities similar to those of elemental metals. Liquid forms are also metallic conductors or electricity, for instance [[Mercury (element)|mercury]]. In normal conditions no gases are metallic conductors. However, a [[plasma (physics)|plasma]] is a metallic conductor and the charged particles in a plasma have many properties in common with those of electrons in elemental metals, particularly for white dwarf stars.<ref>{{Cite journal |last1=Koester |first1=D |last2=Chanmugam |first2=G |date=1990 |title=Physics of white dwarf stars |url=https://iopscience.iop.org/article/10.1088/0034-4885/53/7/001 |journal=Reports on Progress in Physics |volume=53 |issue=7 |pages=837–915 |doi=10.1088/0034-4885/53/7/001 |issn=0034-4885|url-access=subscription }}</ref>

Metals are relatively good [[thermal conductivity|conductors of heat]], which in metals is transported mainly by the conduction electrons.<ref name=bassani>{{cite book | last=Skośkiewicz | first=T. | title=Encyclopedia of Condensed Matter Physics | chapter=Thermal Conductivity at Low Temperatures | publisher=Elsevier | date=2005 | pages=159–164 | isbn=978-0-12-369401-0 | doi=10.1016/b0-12-369401-9/01168-2}}</ref> At higher temperatures the electrons can occupy slightly higher energy levels given by [[Fermi–Dirac statistics]].<ref name="Ashcroft-1976" /><ref name="Solymar-2004" /> These have slightly higher momenta ([[kinetic energy]]) and can pass on thermal energy. The empirical [[Wiedemann–Franz law]] states that in many metals the ratio between thermal and electrical conductivities is proportional to temperature, with a proportionality constant that is roughly the same for all metals.<ref name="Ashcroft-1976" />
[[File:Battery Demonstration Unit - DPLA (cropped).jpg|alt=Battery demonstration unit for conducting polymers built by nobel laureate Alan MacDiarmid|thumb|Battery demonstration unit for conducting polymers built by nobel laureate [[Alan MacDiarmid]]<ref>{{Cite web |title=The Nobel Prize in Chemistry 2000 |url=https://www.nobelprize.org/prizes/chemistry/2000/summary/ |access-date=2024-07-23 |website=NobelPrize.org |language=en-US}}</ref>]]
The contribution of a metal's electrons to its heat capacity and thermal conductivity, and the electrical conductivity of the metal itself can be approximately calculated from the [[free electron model]].<ref name="Ashcroft-1976" /> However, this does not take into account the detailed structure of the metal's ion lattice. Taking into account the positive potential caused by the arrangement of the ion cores enables consideration of the [[electronic band structure]] and [[binding energy]] of a metal. Various models are applicable, the simplest being the [[nearly free electron model]].<ref name="Ashcroft-1976" /> Modern methods such as [[density functional theory]] are typically used.<ref>{{Cite web |last=Burke |first=Kieron |date=2007 |title=The ABC of DFT |url=https://dft.uci.edu/doc/g1.pdf}}</ref><ref>{{Cite book |last1=Gross |first1=Eberhard K. U. |url=https://books.google.com/books?id=aG4ECAAAQBAJ&q=density+functional+theory |title=Density Functional Theory |last2=Dreizler |first2=Reiner M. |date=2013 |publisher=Springer Science & Business Media |isbn=978-1-4757-9975-0 |language=en}}</ref>

===Chemical===
The elements which form metals usually form [[cations]] through electron loss.<ref name="morty"/> Most will react with oxygen in the air to form [[oxide]]s over various timescales ([[potassium]] burns in seconds while iron [[rust]]s over years) which depend upon whether the native oxide forms a [[Passivation (chemistry)|passivation layer]] that acts as a [[diffusion barrier]].<ref>{{Cite book |last1=Bockris |first1=J. O'M |title=Modern electrochemistry. 2 |last2=Reddy |first2=Amulya K. N. |date=1977 |publisher=Plenum Pr |isbn=978-0-306-25002-6 |edition=3. print |location=New York}}</ref><ref>{{Cite book |last1=Kelly |first1=Robert G. |url=https://www.taylorfrancis.com/books/9780203909133 |title=Electrochemical Techniques in Corrosion Science and Engineering |last2=Scully |first2=John R. |last3=Shoesmith |first3=David |last4=Buchheit |first4=Rudolph G. |date=2002-09-13 |publisher=CRC Press |isbn=978-0-203-90913-3 |edition=0 |language=en |doi=10.1201/9780203909133}}</ref> Some others, like [[palladium]], [[platinum]], and [[gold]], do not react with the atmosphere at all; gold can form compounds where it gains an electron (aurides, e.g. [[caesium auride]]). The [[oxide]]s of elemental metals are often [[base (chemistry)|basic]]. However, oxides with very high [[oxidation state]]s such as CrO<sub>3</sub>, Mn<sub>2</sub>O<sub>7</sub>, and OsO<sub>4</sub> often have strictly acidic reactions; and oxides of the less electropositive metals such as BeO, Al<sub>2</sub>O<sub>3</sub>, and PbO, can display both basic and acidic properties. The latter are termed [[amphoteric]] oxides.