Semi-metal

Along with metals and non-metals, semimetals (also known as metalloids) comprise one of three categories of chemical elements following a classification according to the bonding and ionization properties. They are characterized by presenting an intermediate behavior between metals and non-metals, sharing characteristics of both. As a general rule and in most cases, they tend to chemically react with non-metals, although there are certain compounds made up of metal and semi-metal, such as magnesium boride. They can be both shiny and dull, and their shape can be easily changed. Metalloids are generally better conductors of heat and electricity than nonmetals, but not as well as metals. There is no clear way to distinguish metalloids from true metals, but they generally differ in that metalloids are semiconductors rather than conductors. Unlike metals, whose electrical conductivity decreases with increasing temperature, in semi-metals increasing the temperature means the opposite, increasing their electrical conductivity. Nonmetals are opaque and of various colors. They are often used on occasions to form alloys. They can be amphoteric or slightly acidic.

The following elements are considered metalloids:

• Boro (B)
• Silicon (Yes)
• Germanio (Ge)
• Arsenico (As)
• Telurio (Te)
• Polonio (Po)
• Antimony (Sb)

Within the periodic table, the metalloids are found in a diagonal line from boron to astate (the latter is not included). The elements on the top right are nonmetals, and the ones on the bottom left are metals.

All of these elements have three or more valence electrons in their last orbit (B 3, Si 4, Ge 4, As 5, Sb 5, Te 6, Po 6). Silicon, for example, is a metalloid widely used in the manufacture of semiconductor elements for the electronics industry, such as rectifiers, diodes, transistors, integrated circuits, and microprocessors.

Definitions

Based on judgment

A metalloid is an element that possesses a preponderance of intermediate properties, or that are a mixture of those of metals and nonmetals, and is therefore difficult to classify as a metal or a nonmetal. It is a generic definition that is based on the attributes of the metalloids that are systematically cited in the literature.

The following are definitions and extracts from different authors, illustrating aspects of the generic definition:

• "In chemistry a metaloid is an element with intermediate properties between metal and non-metal properties"
• "Among the metals and non-metals of the periodic table we find elements... [that] share some of the characteristic properties of both metals and non-metals, which makes it difficult to place them in any of these two main categories"
• "Chemists sometimes use the name of metaloid for these elements that are difficult to classify in one way or another"
• "Since the features that distinguish non-metal metals are of a qualitative nature, some elements do not fall unequivocally into either of the two categories. These elements... are called metaloids..."

More broadly, metalloids have been referred to as:

• "elements that... are a kind of cross between metals and not metals"; or
• "intermediate strange elements."

Difficulty of categorization is a key attribute. Most elements have a mix of metallic and non-metallic properties, and can be classified based on which set of properties is more pronounced.

Gold, for example, has mixed properties but is still recognized as the "king of metals". In addition to metallic behavior (such as high electrical conductivity, and cation formation), gold shows non-metallic behavior:

• It has the highest potential of electrode]
• It has the third largest ionization energy among metals (after zinc and mercury)
• It has the highest affinity of electron
• Its 2.54 electro-negativida is the largest among metals and exceeds that of some semimetalles (hydrogen 2.2; phosphorus 2.19; and radon 2.2)
• Form auride anion Au⁻where in this case acts as a halogen
• Sometimes it presents a tendency, called "aurophilicity", to link with itself.

On its halogen nature see Belpassi et al., who indicate that in their MAu aurids (M = Li–Cs) gold "behaves as a halogen, intermediate between Br and I"; on aurophilicity see Schmidbaur and Schier.

Only elements at or near the margins, lacking a sufficiently clear preponderance of metallic or non-metallic properties, are classified as metalloids.

Boron, silicon, germanium, arsenic, antimony, and tellurium are usually identified as metalloids. Depending on the author, one or more of selenium, polonium, or astatin are sometimes added to the list. boron, alone or with silicon. Tellurium is sometimes not considered a metalloid. The inclusion of antimony, polonium, and astatine as metalloids has been questioned.

Other elements are occasionally classified as metalloids. These elements include hydrogen, beryllium, nitrogen, phosphorus, sulfur, zinc, gallium, tin, iodine, lead, bismuth, and radon. The term metalloid has also been used for elements that exhibit metallic luster and electrical conductivity, and that are amphoteric, such as arsenic, antimony, vanadium, chromium, molybdenum, tungsten, tin, lead, and copper. aluminum. The p-block metals and nonmetals (such as carbon or nitrogen) that can form alloys with metals or modify their properties have also occasionally been considered metalloids.

Based on criteria

There is no widely accepted definition of a metalloid, nor is there any division of the periodic table into metals, metalloids, and nonmetals; Hawkes questioned the feasibility of establishing a specific definition, noting that anomalies can be found in several attempted constructions. The classification of an element as a metalloid has been described by Sharp as "arbitrary".

The number and identities of the metalloids depend on the classification criteria used. Emsley recognized four metalloids (germanium, arsenic, antimony, and tellurium); James et al. listed twelve (Emsley's plus boron, carbon, silicon, selenium, bismuth, polonium, muscovium, and livermorium). On average, seven elements are included in the lists of metalloids; individual classification arrangements tend to share common ground and vary within ill-defined margins.

A single quantitative criterion such as electronegativity is often used, metalloids have electronegativity values of 1.8 or 1.9 to 2.2. Other examples include packing efficiency (the volume fraction in a structure crystalline occupied by atoms) and the ratio of the Goldhammer-Herzfeld criterion. Commonly recognized metalloids have packing efficiencies of between 34% and 41%.

Other authors have based themselves, for example, on atomic conductance or global coordination number.

Jones, writing about the role of classification in science, noted that "[classes] are generally defined by more than two attributes". Masterton and Slowinski used three criteria to describe the six elements commonly recognized as metalloids: metalloids have ionization energies around 200 kcal/mol (837 kJ/mol) and electronegativity values near 2.0. They also said that metalloids are typically semiconductors, although antimony and arsenic (semimetals from a physical perspective) have electrical conductivities that approach those of metals. Selenium and polonium are suspected to be missing from this scheme, while the status of astatin is uncertain.

In this context, Vernon proposed that a metalloid is a chemical element that, in its standard state, has (a) the electronic band structure of a semiconductor or semimetal; and (b) a first intermediate ionization potential "(say 750-1,000 kJ/mol)"; and (c) an intermediate electronegativity (1.9-2.2).