User:Sandbh/List of nonmetal meanings

The term nonmetal has several meanings, listed from general to more specific, as follows:


 * Chemical elements that mostly lack the distinctive characteristics of metals. This is the definition found in most dictionaries.
 * A semiconductor or insulator. These are substances that do not conduct electricity as well as metals.
 * A material in which electrical conductivity tends to zero for a temperature of absolute zero.
 * In astronomy, the elements hydrogen and helium. In this context, all other elements prevalent in stars and interstellar space are regarded as metals.

A related term is nonmetallic material which refers to solid and liquid compounds and elements that do not exhibit the properties of metals. These materials include ceramics, polymers, and possibly some composites.

Chemical elements that are nonmetals
In chemistry, a nonmetal is a chemical element that mostly lacks distinctive metallic properties. They range from colorless gases like hydrogen to shiny crystals like iodine. Physically, they are usually lighter (less dense) than elements that form metals and are often poor conductors of heat and electricity. Chemically, nonmetals have relatively high electronegativity (meaning they usually attract electrons in a chemical bond with another element), and their oxides tend to be acidic.

Semiconductors or insulators
A nonmetal is a semiconductor such as selenium or lead telluride (PbTe), or an insulator such as nitrogen or copper(I) chloride (CuCl).

A semiconductor is a material that has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass, hydrogen or carbon dioxide. An insulator is a substance that is a poor conductor of heat and electricity.


 * "Over a period of more than half a century, Prof. Sir Nevill Mott pioneered the development of key concepts, models and theories for discussing the fundamental problem of metals versus non-metals (insulators and semiconductors)."

A material in which electrical conductivity tends to zero at T = 0
Whereas metals are materials and substances in which the conductivity tends to a finite value for absolute zero (or infinite in the case of a superconductor), the term "nonmetal" describes those for which the conductivity tends to zero for absolute zero. At such low temperatures all substances are either solid or liquid, most notably in the case of liquid helium, which only solidifies under pressure.

In astronomy, the elements hydrogen and helium
The astrophysicst Carlos Jaschek, and the stellar astronomer and spectroscopist Mercedes Jaschek, in their book The Classification of Stars, observed that:
 * "Metals: (a term which is used very equivocally). Stellar interior specialists use 'metals' to designate any element other than hydrogen and helium, and in consequence ‘metal abundance’ implies all elements other than the first two. For spectroscopists this is very misleading, because they use the word in the chemical sense. On the other hand photometrists, who observe combined effects of all lines (i.e. without distinguishing the different elements) often use this word 'metal abundance', in which case it may also include the effect of the hydrogen lines. It is important to make sure in each particular case what the author really meant."

Nonmetallic materials
Nonmetallic materials encompass solid and liquid compounds and elements that do not exhibit the properties of metals. These materials include ceramics, polymers, and certain composites.

While there are many mentions of “non-metallic materials” in the literature, it is the aims and scope statement for Nature Materials that clarifies that gases, by their omission, are generally not counted as "materials":


 * Nature Materials is a monthly multi-disciplinary journal aimed at bringing together cutting-edge research across the entire spectrum of materials science and engineering. Materials research is a diverse and fast-growing discipline, which has moved from a largely applied, engineering focus to a position where it has an increasing impact on other classical disciplines such as physics, chemistry and biology. Nature Materials covers all applied and fundamental aspects of the synthesis/processing, structure/composition, properties and performance of materials, where "materials" are identified as substances in the condensed states (liquid, solid, colloidal) designed or manipulated for technological ends.