Metalloids, also known as semimetals, occupy a unique position in the periodic table. They exhibit properties that are intermediate between metals and nonmetals, making them versatile and valuable in various industrial and technological applications. This guide explores the fundamental properties of metalloids, their occurrence, and their applications.
Introduction to Metalloids
Metalloids are elements with properties that are intermediate between metals and nonmetals. They are located along the zig-zag line on the periodic table, which separates metals from nonmetals. Typically including boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). Sometimes, polonium (Po) and astatine (At) are also considered metalloids.
Historical Use of Metalloid
Metalloids have been used for centuries:
- Antimony: Used in ancient Egypt for makeup and as a colorant; classified as a metalloid in the 1500s.
- Arsenic: Likely first isolated by Albertus Magnus around 1250; used as a pigment until its toxicity was discovered.
- Silicon: Discovered in 1823 by Jöns Jacob Berzelius; first commercially available semiconductors were produced in 1954.
Which Elements Are Metalloids?
Metalloids are elements with properties intermediate between metals and nonmetals. The universally accepted metalloids are:
- Boron (B)
- Arsenic (As)
- Germanium (Ge)
- Tellurium (Te)
- Antimony (Sb)
- Silicon (Si)
Some scientists also include the following elements as metalloids, though their classification can be debated:
- Astatine
- Polonium
- Bismuth
What are the Main Properties of Metaloids?
Metalloids, exhibit properties that are intermediate between metals and nonmetals. This blend of characteristics makes them essential in various applications, especially in electronics and materials science. Here are the main properties of metalloids:
Metallic Luster
Metalloids possess a shiny, metallic appearance, which makes them look similar to metals. This characteristic metallic luster is the result of their ability to reflect light effectively. When light strikes the surface of a metalloid, it interacts with the free electrons present in the material. These electrons oscillate and re-emit the light, giving the material its shiny, reflective quality.
However, their appearance can vary; some metalloids like arsenic and antimony can present in different forms, including crystalline or powdery states.
| Image Example | Elements |
|---|---|
 | Boron (B) |
 | Silicon (Si) |
 | Germanium (Ge) |
 | Arsenic (As) |
 | Tellurium (Te) |
 | Antimony (Sb) |
Solid State at Room Temperature
All metalloids are solid at room temperature and have relatively high melting points.
- Boron (B): Melting point of 2079°C
- Silicon (Si): Melting point of 1410°C
- Germanium (Ge): Melting point of 938.3°C
- Arsenic (As): Melting point of 817°C
- Tellurium (Te): Melting point of 449.5°C
- Antimony (Sb): Melting point of 631°C
Brittleness
Unlike metals, which are typically malleable and ductile, metalloids tend to break or shatter when subjected to stress or force. This brittleness means they cannot be shaped or formed using typical metal-forming techniques such as hammering, rolling, or bending.
Hardness
Metalloids can be relatively hard compared to non-metals.
- Boron (B): Known for being one of the hardest substances, with a hardness of about 9.3 on the Mohs scale.
- Silicon (Si): Moderately hard with a hardness of about 7 on the Mohs scale, valued in semiconductor applications due to its balance of hardness and electrical properties.
- Germanium (Ge): Hardness of approximately 6 on the Mohs scale.
- Arsenic (As): Soft with a hardness of around 3.5 on the Mohs scale.
- Tellurium (Te): Soft with a hardness of about 2.5 on the Mohs scale.
- Antimony (Sb): Soft and brittle with a hardness of about 3 on the Mohs scale.
Semiconductor Properties
Metalloids can conduct electricity, but not as efficiently as metals. This property makes them useful as semiconductors, essential for electronic devices. The conductivity of metalloids can be enhanced through a process called “doping,” where impurities are added to modify their electrical properties.
Chemical Behavior Similar to Nonmetals
Metalloids tend to form anions, exhibit multiple oxidation states, and form covalent bonds. They share electrons when forming compounds.
Example oxidation states:
- Boron (B): +3, +2, +1
- Silicon (Si): +4, 0
- Germanium (Ge): +2, +4
- Arsenic (As): +3, +5
- Tellurium (Te): +4, +6
- Antimony (Sb): +3, +5
Intermediate Ionization Energies and Electronegativities
Metalloids have ionization energies and electronegativities that lie between those of metals and nonmetals. Ionization energy is the energy required to remove an electron from an atom, while electronegativity is a measure of an atom’s ability to attract electrons in a chemical bond.
Example values:
- Boron (B): 1st Ionization Energy: 8.298 eV, Electronegativity: 2.04
- Silicon (Si): 1st Ionization Energy: 8.1517 eV, Electronegativity: 1.9
- Germanium (Ge): 1st Ionization Energy: 7.9 eV, Electronegativity: 2.01
- Arsenic (As): 1st Ionization Energy: 9.8152 eV, Electronegativity: 2.18
- Tellurium (Te): 1st Ionization Energy: 9.0096 eV, Electronegativity: 2.1
- Antimony (Sb): 1st Ionization Energy: 8.64 eV, Electronegativity: 2.05
Density
Density is the mass per unit volume of a substance. For metalloids, the densities vary significantly:
- Boron (B): Density of 2.46 g/cm³
- Silicon (Si): Density of 2.33 g/cm³
- Germanium (Ge): Density of 5.32 g/cm³
- Arsenic (As): Density of 5.73 g/cm³
- Tellurium (Te): Density of 6.24 g/cm³
- Antimony (Sb): Density of 6.69 g/cm³
Physical Properties of Metalloids
Metalloids have a distinct set of physical properties that reflect their intermediate position between metals and non-metals. The following table clearly displays its characteristics.
| Property | Boron | Silicon | Germanium | Arsenic | Antimony | Tellurium |
|---|---|---|---|---|---|---|
| Appearance | Dark brown, metallic | Metallic-gray | Metallic-gray | Metallic-gray | Silvery-gray | Metallic-gray |
| Density | 2.46 g/cm³ | 2.33 g/cm³ | 5.32 g/cm³ | 5.72 g/cm³ | 6.70 g/cm³ | 6.24 g/cm³ |
| Melting Point | 2075°C | 1414°C | 938°C | 817°C (sublimes) | 631°C | 449.5°C |
| Boiling Point | 4000°C | 2355°C | 2833°C | 614°C | 1587°C | 988°C |
| Hardness | Very hard | Hard | Moderate | Variable | Moderate | Moderate |
| Electrical Conductivity | Poor (non-metallic) | Moderate (semiconductor) | Moderate (semiconductor) | Poor (non-metallic) | Poor (non-metallic) | Poor (non-metallic) |
| State at Room Temperature | Solid | Solid | Solid | Solid | Solid | Solid |
| Crystal Structure | Various (e.g., amorphous, crystalline) | Diamond cubic | Diamond cubic | Various (e.g., gray, yellow) | Rhombohedral | Trigonal |
| Atomic Number | 5 | 14 | 32 | 33 | 51 | 52 |
| Electronegativity | 2.04 | 1.90 | 2.01 | 2.18 | 2.05 | 2.01 |
| Uses | Abrasives, borosilicate glass | Semiconductors, solar cells | Semiconductors, infrared optics | Pesticides, semiconductors | Alloys, flame retardants | Thermoelectric devices |
Chemical Properties of Metalloids
Metalloids exhibit a range of chemical properties that reflect their intermediate nature. They have moderate electronegativity and ionization energy, can display multiple oxidation states, and react with both acids and bases. Their chemical behavior can be complex, often depending on the specific conditions and compounds involved.
| Property | Boron | Silicon | Germanium | Arsenic | Antimony | Tellurium |
|---|---|---|---|---|---|---|
| Electronegativity | 2.04 | 1.90 | 2.01 | 2.18 | 2.05 | 2.1 |
| Ionization Energy | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate |
| Oxidation States | +3 | +4 | +2, +4 | +3, +5 | +3, +5 | +2, +4, +6 |
| Reactivity with Acids | Generally unreactive | Reacts with strong bases, less with acids | Reacts with acids and bases | Reacts with acids, forms arsenic acids | Reacts with acids and bases | Reacts with acids, forms telluric acid (H₂TeO₄) |
| Reactivity with Bases | Reacts with strong bases when heated | Reacts with strong bases | Reacts with acids and bases | Forms arsenides | Forms antimony trichloride and pentachloride | Forms tellurides with strong bases |
| Oxides | Boron oxide (B₂O₃) | Silicon dioxide (SiO₂) | Germanium dioxide (GeO₂) | Arsenic trioxide (As₂O₃) | Antimony trioxide (Sb₂O₃) | Tellurium dioxide (TeO₂), Tellurium tetroxide (TeO₄) |
| Hydrides | Boranes (e.g., B₂H₆) | Silanes (e.g., SiH₄) | Germane (GeH₄) | Arsine (AsH₃) | Stibine (SbH₃) | Tellurium hydride (TeH₂) |
| Halides | Boron trichloride (BCl₃) | Silicon tetrafluoride (SiF₄) | Germanium tetrachloride (GeCl₄) | Arsenic trichloride (AsCl₃), pentachloride (AsCl₅) | Antimony trichloride (SbCl₃), pentachloride (SbCl₅) | Tellurium tetrachloride (TeCl₄), Tellurium hexafluoride (TeF₆) |
Applications of Metalloids
Metalloids play a critical role in various technological and industrial applications due to their unique properties:
- Electronics: Silicon and germanium are crucial in semiconductor technology. Their ability to control electrical conductivity makes them fundamental in the manufacturing of integrated circuits and solar cells.
- Materials Science: Metalloids like boron are used to improve the hardness and strength of materials. Boron carbide, for example, is used in bulletproof vests and other high-strength applications.
- Chemistry: Metalloids are involved in numerous chemical processes and compounds. For instance, arsenic compounds are used in pesticides and in the semiconductor industry, despite their toxic nature.
Typical Applications of 5 Metalloids
| Element | Description | Typical Applications |
|---|---|---|
| Boron (B) | Dark brown or black, metallic-looking solid; hard, brittle, high melting point | Glass and ceramics, detergents, alloys, nuclear reactors |
| Silicon (Si) | Shiny, metallic-gray solid; brittle, hard, moderate electrical conductivity | Electronics (semiconductors), solar cells, construction (concrete), silicones |
| Germanium (Ge) | Grayish-white, metallic-looking solid; brittle, semiconductor properties | Electronics (transistors, diodes), optics (infrared lenses), fiber optics |
| Arsenic (As) | Gray metallic solid or yellow powder; toxic, various compounds | Pesticides (historically), semiconductors (gallium arsenide), wood preservation |
| Antimony (Sb) | Shiny, silvery-gray metal; brittle, low melting point | Alloys (lead-acid batteries), flame retardants, semiconductors |
| Tellurium (Te) | Silvery-white, brittle solid; semiconductor properties, high density | Electronics (semiconductors), solar panels (CdTe cells), metallurgy |
What Distinguishes Metalloids?
Metalloids are distinguished by their properties that fall between metals and nonmetals. Key characteristics include:
- Intermediate Properties: Metalloids exhibit a mix of metal and nonmetal properties.
- Semiconducting Ability: They can act as semiconductors, which is crucial for modern electronic circuits.
These unique features make metalloids essential in technology and electronics.
What Is the Best Way to Identify a Metalloid?
The most useful property for identifying a metalloid is its metallic appearance. While metalloids often have a metallic luster, distinguishing them by chemical attributes is more challenging due to the overlap with other elements’ properties.
What Is the Difference Between Metal and Nonmetal?
The differences between metals and nonmetals are fundamental and pertain to their physical and chemical properties. Here’s a comprehensive comparison:
Physical Properties
| Property | Metals | Nonmetals |
|---|---|---|
| Appearance | Shiny and metallic | Dull and non-reflective |
| Density | High (e.g., Iron: 7.87 g/cm³, Gold: 19.32 g/cm³) | Low (e.g., Carbon: 2.267 g/cm³, Oxygen: 0.00143 g/cm³) |
| Melting Point | High (e.g., Tungsten: 3422°C, Iron: 1538°C) | Low (e.g., Oxygen: -218.79°C, Bromine: -7.2°C) |
| Boiling Point | High (e.g., Tungsten: 5555°C, Iron: 2862°C) | Low (e.g., Oxygen: -182.96°C, Bromine: 58.8°C) |
| Hardness | Varies (e.g., Iron: 4.0-4.5 on Mohs scale, Gold: 2.5) | Typically softer (e.g., Sulfur: 1.5-2.0 on Mohs scale) |
| Electrical Conductivity | High (e.g., Copper: 5.96 × 10⁷ S/m) | Low (e.g., Sulfur: 1 × 10⁻¹⁶ S/m) |
| Thermal Conductivity | High (e.g., Copper: 401 W/m·K) | Low (e.g., Sulfur: 0.2 W/m·K) |
| State at Room Temperature | Solid (except mercury: liquid) | Gas (e.g., Nitrogen, Oxygen), liquid (e.g., Bromine), or solid (e.g., Sulfur) |
| Malleability and Ductility | High (e.g., Gold can be hammered into thin sheets) | Low (e.g., Phosphorus: brittle) |
Chemical Properties
| Property | Metals | Nonmetals |
|---|---|---|
| Electronegativity | Low (e.g., Sodium: 0.93, Iron: 1.83) | High (e.g., Fluorine: 3.98, Oxygen: 3.44) |
| Ionization Energy | Low (e.g., Sodium: 495.8 kJ/mol, Iron: 762.5 kJ/mol) | High (e.g., Fluorine: 1681 kJ/mol, Oxygen: 1314 kJ/mol) |
| Oxidation States | Often positive (e.g., Iron: +2, +3; Sodium: +1) | Often negative or zero (e.g., Oxygen: -2, Nitrogen: -3) |
| Reactivity with Acids | Reacts to release hydrogen gas (e.g., Zinc: Zn + 2HCl → ZnCl₂ + H₂) | Generally does not react or forms acids (e.g., Sulfur reacts with bases to form sulfides) |
| Reactivity with Bases | Reacts with bases (e.g., Aluminum reacts with NaOH: 2Al + 2NaOH + 6H₂O → 2NaAl(OH)₄ + 3H₂) | Forms acids with bases or less reactive (e.g., Carbon dioxide reacts with water to form carbonic acid) |
| Formation of Oxides | Basic oxides (e.g., Sodium oxide: Na₂O) | Acidic oxides (e.g., Carbon dioxide: CO₂) |
Which Properties Do Metalloids Share with Nonmetals?
Metalloids share several properties with nonmetals, including:
- High Electronegativity: Metalloids have relatively high electronegativities, similar to nonmetals.
- Formation of Anions: They often gain electrons to form negative ions (anions), a characteristic common to nonmetals.
- Covalent Bonding: Metalloids commonly form covalent bonds, like nonmetals.
- Variable Oxidation States: They can exhibit multiple oxidation states, akin to nonmetals.
These shared properties highlight the intermediate nature of metalloids between metals and nonmetals.
How Do You Categorize a Metalloid?
Metalloids are categorized based on their properties that are intermediate between metals and nonmetals. They are typically positioned along a diagonal line on the periodic table that separates metals from nonmetals. Key characteristics used to categorize metalloids include:
- Appearance: They often have a metallic luster.
- Physical Properties: They are usually solid at room temperature and can be brittle.
- Chemical Properties: They can act as semiconductors and have properties that overlap with both metals and nonmetals.
These factors help in identifying and categorizing metalloids on the periodic table.
Conclusion
Metalloids exhibit a fascinating combination of properties that bridge the gap between metals and non-metals. Their intermediate physical and chemical characteristics, along with their unique electrical properties, make them invaluable in various scientific and industrial fields. As technology advances, the role of metalloids continues to evolve, highlighting their importance in modern science and engineering.
FAQ
The number of metalloids on the periodic table is debated, with counts ranging from six to eleven. The most commonly accepted metalloids are six: boron, silicon, germanium, arsenic, tellurium, and antimony. Some classifications also include polonium, astatine, and bismuth, increasing the number to nine or eleven, depending on the definition used.
Metalloids can both gain and lose electrons, depending on their chemical context. They often gain electrons to form anions or lose electrons to form cations. This ability to gain or lose electrons allows metalloids to form various chemical bonds and exhibit properties of both metals and nonmetals.
They are typically solid at room temperature, have a metallic luster, and can be brittle. Metalloids also exhibit semiconducting behavior, meaning they can conduct electricity but not as well as metals. Additionally, they can form covalent bonds and may gain or lose electrons depending on the chemical context.
Catalog: Materials Guide
This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.
