Metal: properties, types, history, uses, and metallurgy

Traditionally, metals are divided according to density into heavy metals and light metals and according to reactivity into noble metals and base metals, the latter being good reducing agents. See also the main article Metallic material (and on reactivity under Redox reaction).

Metals are formed by the elements that are located in the periodic table of the elements in the area to the left and below a line from boron to astatine, whereby the metallic character increases from top to bottom or from right to left. At the very top right are the nonmetals, with the semimetals in between. The subgroup elements form metals without exception. The border to the non-metals is fluid. For example, antimony, arsenic, cerium, and tin have both metallic and nonmetallic modifications.

The affiliation to main or subgroups of the periodic table is also decisive for the chemical behaviour.

General

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

• The number of electrons in the outer shell is small and smaller than the coordination number
• The ionization energy (necessary to split off these outer electrons) is small (< 10 eV).

As a result, such atoms cannot bond with each other via atomic bonds to form molecules or lattices. At most, atomic bonds occur in metal vapours, e.g. sodium vapour consists of about 1 % Na2 molecules.

Rather, metal atoms arrange themselves into a metal lattice consisting of positively charged atomic trunks, while the valence electrons are distributed throughout the lattice; none of these electrons belongs to a particular nucleus anymore. These freely moving electrons can be thought of as particles of a gas that fills the space between the atomic trunks. Since this electron gas, among other things, causes the good electrical conductivity of metals, the energy level at which the free electrons are found is called the "conduction band." The exact energetic conditions are described by the band model based on the orbital model.

This type of bonding and this lattice structure result in the following typical properties of the metals:

• Shine (mirror shine): The freely moving electrons can re-emit almost all of the incident electromagnetic radiation up to wavelengths of X-rays; this is how the shine and reflection are created; mirrors are therefore made from smooth metal surfaces.
• Opacity: The aforementioned reflection taking place on the metal surface and the absorption of the non-reflected portion have the effect that, for example, light can hardly enter metal. Metals are therefore only somewhat translucent in the thinnest layers and appear grey or blue when seen through.
• Good electrical conductivity: The migration of freely moving electrons in one direction is the electric current.
• Good thermal conductivity: The easily displaceable electrons participate in the thermal motion. They also transfer the inherent thermal motion of the atomic hulls (oscillations) and thus contribute to heat transport, cf. heat conduction.
• Good formability (ductility): there are grain boundaries and dislocations in the metal which can already move at an elongation below the breaking elongation, i.e. without losing cohesion; depending on the type of lattice, a metal therefore deforms before it breaks.
• Relatively high melting point: It results from the omnidirectional bonding forces between the cations and the freely moving electrons, but a less strong effect than the electrostatic attraction forces between ions in salt crystals.

Melting and boiling temperatures

Metals whose melting point _TE is above 2000 K or above the melting point of platinum (_{TE platinum} = 2045 K = 1772 °C) are described as having a high melting point. 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).

Heat conduction properties

The properties relevant to thermal 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 about 50 times higher than manganese, see list of values.