Maybe you are familiar with the easy term of metal and nonmetal but never heard of metalloids. Then what are metalloids? Here is what we are going to talk about in this article. Simply put, the term “metalloids” refers to elements that have properties intermediate between metals and nonmetals. They are located along the stair-step line in the periodic table, separating metals and nonmetals. Generally, metalloids have a metallic look but behave more like nonmetals in most chemical reactions. They are very useful for applications that require moderate conductivity, hardness, and chemical reactivity.
If you are researching the topic of metalloids, maybe this article will give you some inspiration and help. This post mainly explains the definition, elements, properties, and uses of metalloids. Read on and get more contents you want to learn.
What are Metalloids?
Metalloid is derived from the Latin metallum (“metal”) and the Greek oeides (“resembling in form or appearance”). A metalloid represents a chemical element exhibiting properties that are intermediate between those of metals and nonmetals. Or we can say they are a mixture of metals and nonmetals. Elements classified as metalloids are frequently highlighted in what is known as the “Metalloid Stair Step” because when colored differently from the other elements, this group of elements resembles a staircase.
The six most often recognized examples of metalloids cover boron, silicon, germanium, arsenic, antimony, and tellurium. And there are five elements, such as carbon, aluminum, selenium, polonium, and astatine are seldom categorized into metalloids. All eleven elements can be found on the standard periodic table. They are located in a diagonal region of the p-block ranging from boron at the upper left to astatine at the lower right. On some periodic tables, metalloids can be found near the dividing line between metals and nonmetals.
Metalloids have a metallic look, yet they are brittle and only electrical conductors with a level of intermediate to good. Chemically, they mainly act like nonmetals. They can combine with metals to make alloys. The majority of their other chemical and physical properties tend to be intermediate. Metalloids are often too brittle to be used in structural applications. However, metalloids and their compounds are always employed in alloys, biological agents, catalysts, flame retardants, glasses, optical storage, optoelectronics, pyrotechnics, semiconductors, and electronics.
What are the Typical Elements of Metalloids?
Metalloids are elements located between metals and nonmetals in the periodic table. They have properties that are a mix of metals and nonmetals. The most well-known metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. They form a diagonal band separating metals from nonmetals. The following is a detailed introduction to the typical elements of metalloids.
Boron (B)
Boron is a chemical element. Its symbol is B, and its atomic number is 5. It contains various compounds, including boric acid, the mineral sodium borate, and ultra-hard crystals of boron carbide and boron nitride. Boron has several allotropes: amorphous boron and crystalline boron. Generally, amorphous boron is a brown powder, While crystalline boron is silvery to black, highly hard, and a poor electrical conductor at room temperature.
The major application of the elemental itself is as boron filaments. In addition, it is an additive in fiberglass, which is used for insulation and structural materials. Borosilicate glass is favored because it is stronger and more resistant to thermal shock than soda lime glass. Sodium perborate can serve as a bleach. Borates have little toxicity in mammals but are toxic to arthropods and are occasionally employed as insecticides. It is a necessary plant nutrient.
Arsenic (As)
Arsenic is a chemical element with the atomic number 33 and As symbol. Arsenic often combines with sulfur and metals, yet it can also be a pure elemental crystal. Arsenic is classified as a metalloid with several allotropes, but only the gray form with a metallic appearance is prevalent in the industry.
The principal application of arsenic is in lead alloys, such as automotive batteries and ammunition. Arsenic and its compounds, particularly trioxide, are utilized in manufacturing pesticides, treated wood products, herbicides, and insecticides.
Arsenic compounds can be adopted as respiratory metabolites by a few bacteria species. For example, arsenic is an important dietary element for goats, chickens, and other species. However, arsenic poisoning occurs in multicellular life when the amount exceeds what is required.
Silicon (Si)
Silicon is a chemical element with the atomic number 14 and the symbol Si. It is a hard and brittle crystalline solid with a blue-grey metallic luster. Silicone is a tetravalent metalloid and semiconductor.
Silicon occurs relatively seldom as a pure element in the Earth’s crust. It often exists in different forms of silicon dioxide (silica) or silicates and is extensively spread in space in cosmic dust, planetoids, and planets. After oxygen, silicon is the second most abundant element in the Earth’s crust.
Pure silicon is extremely reactive, and its derivatives are frequently found in sands, rocks, and soils. It is widely utilized in semiconductors and producing alloys, glass, enamels, and other ceramics.
Antimony (Sb)
The chemical element antimony has the symbol Sb and atomic number 51. It is a glossy gray metalloid found mostly in nature as the sulfide mineral stibnite. Since ancient times, antimony compounds have been powdered for use in medicine and cosmetics.
Major uses for metallic antimony are in alloys with lead and tin that enhance the properties of solders, bullets, and plain bearings. It makes lead-alloy plates in lead-acid batteries more rigid. Antimony trioxide is a common additive in halogen-containing flame retardants. In semiconductor devices, antimony is employed as a dopant.
Tellurium (Te)
Tellurium is a chemical element with the atomic number 52 and the symbol Te. It is a silver-white metalloid that is brittle and somewhat toxic. Tellurium is sometimes discovered in its native state as elemental crystals.
Tellurium is far more prevalent in the universe than it is on Earth. Its high scarcity in the Earth’s crust is equivalent to platinum. This is partly attributed to the creation of a volatile hydride, which led tellurium to be lost to space as a gas during the hot nebular formation of Earth.
Germanium (Ge)
The symbol for the chemical element germanium is Ge, and its atomic number is 32. It is glossy, hard-brittle, grayish-white, and resembles silicon in appearance. Germanium is a metalloid in the carbon group, and its chemical properties are similar to silicon and tin. In general, naturally occurring germanium compounds are insoluble in water.
Elemental germanium acts as a semiconductor used in transistors and other electronic devices. And the most common applications of germanium include fiber-optic systems, infrared optics, solar cell applications, and light-emitting diodes. Additionally, germanium compounds are utilized as polymerization catalysts.
What are the Properties of Metalloids?
In general, Metalloids have the appearance of metals. They are typically brittle and hard and behave as semiconductors. Chemically, metalloids tend to function similarly to nonmetals. Therefore, metalloids are rarely used for mechanical applications. However, this behavior is dependent on the exact elements they react to. This means that metalloids behave as nonmetals in certain chemical reactions and as metals in others.
Physical Properties of Metalloids
The physical properties of metalloids are often a combination of metal and nonmetal properties. Some of the physical properties of metalloids are as follows:
Appearance: Metalloids have a metallic luster and are brittle solids at room temperature. They appear lustrous and metallic but are brittle enough to shatter. For instance, silicon is a hard, brittle crystalline solid with a blue-grey metallic luster. Antimony is a silvery, lustrous gray metalloid.
Boiling and Melting Points: Metalloids have intermediate boiling and melting points compared to metals and nonmetals. For example, silicon has a melting point of 1410 °C and boron is 2079 °C, while germanium is 938.3 °C. These points are lower than most metals but higher than nonmetals.
Density: Metalloid densities vary but are generally lower than metals and higher than nonmetals. For example, the densities of antimony and tellurium are 6.697 g/cm3 and 6.24 g/cm3, respectively, while arsenic is 5.727 g/cm3.
Electrical Conductivity: Metalloids are not as good conductors of electricity as metals. In reality, several metalloids exhibit semiconductor properties. This implies that they can be conductors or insulators depending on the impurity levels or temperature effects. However, their conductivity is higher than most nonmetal elements. For example, silicon and germanium are semiconductors with conductivity between nonmetals and metals.
Allotropes: Several metalloids exhibit allotropy or different forms with different physical properties. The three most common arsenic allotropes are gray, yellow, and black arsenic, with gray being the most common.
Thermal Conductivity: Metalloids are superior heat conductors to nonmetals but inferior to metals. The thermal conductivity of metalloids varies depending on the specific element. In comparison, some metalloids exhibit low thermal conductivity, while others display higher thermal conductivity. This property is utilized in the manufacturing of thermoelectric devices.
Brittleness: Unlike most metals, which are malleable and ductile, metalloids tend to be brittle. This means they can break or shatter easily when stressed or forced.
Hardness: Metalloids come in a variety of hardnesses. For instance, the Mohs hardness of arsenic is 3.5, while that of boron is 9.3. In contrast, diamond has a Mohs hardness of 10, whereas gold has a Mohs hardness of 2.5.
Chemical Properties of Metalloids
Metalloids will typically behave chemically like nonmetals. Some typical chemical properties of metalloids are listed below:
Reactivity with Nonmetals: Metalloids are chemically reactive and tend to gain or lose electrons to form negatively or positively charged ions, respectively. They readily form compounds, especially with nonmetals. For example, silicon reacts with halogens to form silicon tetrahalides, and boron forms boron trifluoride with fluorine.
Oxidation States: Common oxidation states of metalloids include +3, +2, -4, and -2. For example, boron exhibits +3 in boron trichloride, while silicon is -4 in silicon dioxide. Arsenic and antimony commonly exhibit +3 and +5 oxidation states.
Electronegativity: Electronegativity is the ease with which an atom attracts elements when creating a chemical bond. The higher the number, the more powerful the attraction. Metalloids generally have electronegativity values ranging from 1.8 to 2.2. This intermediate electronegativity gives metalloids the ability to form ionic and covalent bonds.
Covalent Bonds: Metalloids make covalent bonds but do not produce monatomic ions like metals.
Alloy Formation: Metalloids can be mixed with other metals to create alloys. Antimony is combined with lead to make antimonial lead alloys used in ammunition.
Reactivity with Acids: Most metalloids do not react vigorously with acids. For example, silicon, germanium, and polonium do not react with most acids due to their insolubility and formation of a protective oxide layer. However, arsenic, antimony, and bismuth react with strong oxidizing acids like nitric acid. Hydrochloric acid does not oxidize them.
What are the Uses of Metalloids?
Metalloids have unique physical and chemical properties that make them important in various applications. Here are some of the most common applications of metalloids:
Semiconductors: Silicon and germanium are essential for semiconductors in electronics like integrated circuits, computer chips, and solar cells. Their semiconducting properties play a pivotal role in electronics. Silicon semiconductors are used in cell phones, computers, automotive electronics, and many other devices.
Glass and ceramics: Boron, silicon, and arsenic are added to glass and ceramic compositions as fluxes and refractory agents. Borosilicate glass, like Pyrex, is resistant to thermal shock and chemicals. Silicon and phosphorus are added to stoneware and ceramic glazes.
Alloys: Metalloids like silicon, boron, and arsenic are added to alloys to improve their properties. Silicon is added to aluminum alloys to improve their strength and castability. Boron is added to steel alloys to increase hardness and strength. Lead-antimony alloys are used in battery grids and solders.
Photovoltaics: Silicon and germanium are used in solar cells to convert sunlight into electricity. Crystalline silicon and gallium arsenide are common solar cell materials because they absorb light well and have the proper bandgap for efficiently converting light into useful electrons.
Flame Retardants: Compounds of metalloids such as antimony trioxide, boron compounds, and aluminum trihydrate are added as flame retardants to plastics, textiles, coatings, and building materials. They interfere with combustion to improve fire safety.
Agrochemicals: Arsenic was once used as a pesticide but was banned due to toxicity and environmental hazards. Silicon and boron are added as fertilizers to improve plant growth and crop yields. Boron increases hardness in cell walls, pollination in fruit plants, and drought tolerance. Silicon increases stem strength and resistance to pathogens in grains like rice.
Silicone Rubber: Silicon is polymerized with oxygen to produce a polymer with a silicone-oxygen backbone (polymer branches are generally methyl). Modifying the polymer chain can result in a wide range of properties. Silicone is frequently used as a sealant, lubricant, insulation, and cooking utensil.
Other Uses: Boron fibers are extremely light and strong in aerospace applications. Boron carbide is an extremely hard compound used in tank armor and protective gear. Tellurium and selenium compounds are used in rubber, pigments, explosives, slips, mold releases, and petroleum refining.
Summary
Metalloids exist in the transition zone between metals and nonmetals, showing the properties of both elements. They have a higher thermal or electrical conductivity than nonmetals but not as high as metals. Metalloids resemble metallic in appearance, yet they are brittle and are usually solid at ambient temperatures. Metalloids’ hybrid properties enable various real-world applications, such as metal alloys, catalysts, biological agents, glasses, flame retardants, semiconductors, and electronics.
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References
Metalloid – From Wikipedia
Boron – From Wikipedia
Arsenic – From Wikipedia
Silicon – From Wikipedia
Antimony – From Wikipedia
Tellurium – From Wikipedia
Germanium – From Wikipedia
FAQs
A metalloid is a chemical element with both metal and nonmetal properties. Metalloids constitute a jagged zone in the periodic table, dividing elements with clear metallic properties from elements with clear non-metallic properties.
The most straightforward approach to determine whether an unknown element is a metalloid is to test whether any metal and nonmetal properties can be detected. If both are found, the supplied element is most likely metalloid.
The exact number of metalloid elements on the periodic table is frequently debated, with estimates ranging from six to eleven. The six commonly recognized metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium.
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