July 5, 2022

Metal (Kinzoku, English: metal) is a good conductor of electricity and heat that is rich in malleability and plasticity (ductility) and can be machined, and is a general term for substances with a unique luster called metallic luster. With the exception of mercury, it becomes a solid that is not transparent under normal temperature and pressure, and maintains good conductor properties and gloss even in the liquefied state. An element that has the properties of a metal by itself is called a "metal element", and the atoms inside the metal are in a metal crystal state in which cations called metal bonds are mediated by free electrons. In the periodic table, the element located to the left of the diagonal line connecting boron, silicon, arsenic, tellurium, and astatine (these are called metalloids) corresponds to the metal element. Alloys, which are mixtures of different metals, and phases containing certain non-metals that exhibit metal-like properties are included in metals.


Definition from the nature

Due to its nature, a metal that has all of the following five characteristics is defined as a metal. Solid at room temperature (excluding mercury). It is easy to plastically deform and can be spread. It has an opaque and shiny metallic luster. It conducts electricity and heat well. It becomes a cation (cation) in an aqueous solution. However, it has been pointed out that hydrogen may be in a metallic state under a specific environment other than metal elements. For example, it is speculated that hydrogen takes on metallic properties under a high pressure of 200 GPa at room temperature. This is called metallic hydrogen.

Definition from chemical bonds

When a metal is defined by the chemical bond of an atom, it is explained by a unique metal bond. This refers to a bond in which cationized metal elements are regularly arranged and free electrons move around between them, and these are bonded by Coulomb force, and a substance in such a bonded state at room temperature is defined as a metal. .. In most cases, the atomic arrangement is either face-centered cubic lattice structure (fcc), body-centered cubic lattice structure (bcc), or hexagonal close-packed structure (hcp), depending on the type of element and the state of the same element. It has each structure. Each of these structures has a different atomic packing factor and affects the plastic deformation of the metal. In free electron theory, a metal is a state in which electrons are freely flying around in a grid-like solid formed by protons (Drude, 1900), and a steel sphere (cation) is immersed in a gas of free electrons. The expression (Lorentz, 1923) explained how cations and electron clouds combine and the behavior of free electrons. The presence of this free electron brings about the characteristics of metal. When an external force is applied to an object to cause a shift, the ionic bond substance undergoes electrostatic repulsion and breaks, whereas the metal is surrounded by free electrons, so the bond is stable. Metallic luster is due to the fact that free electrons repel most visible light, and in fact a group of free electrons absorbs and re-emits light of various wavelengths, thus appearing to be totally reflective and glossy. The conductivity is contributed by the transfer of electric charge between the electrodes while the charged electrons move around freely.

Metals in band theory

The level of energy that an electron in an atom can take is an electron orbit that does not overlap in the presence of multiple atoms. The orbits generated by this splitting required by quantum mechanics are filled in order from the place with the lowest energy in the situation where there are as many atoms as Avogadro in the metal, and the electron with the highest energy (Fermi energy) is a spherical Fermi surface. And has a fixed width as a whole. This is called a "band structure".