Where Are Metalloids on The Periodic Table?

What are the metalloids?

Metalloids can be defined as chemical elements whose physical and chemical properties fall in between the metal and non-metal categories.

Boron, germanium, silicon, antimony, arsenic, tellurium and pollanium are the seven most widely recognized metalloids.

It can be noted that all seven of these elements can be found on the regular periodic table in a diagonal region of the p-block which extends from boron (which is placed on the upper left) to astatine (which is placed on the lower right).

Some periodic tables have a dividing line between metals and nonmetals, and below this line, the metalloids can be found.

Typically, metalloids have metallic appearances but they are usually brittle and only mediocre electricity conductors.

Chemically, these elements usually behave as non-metals. Metalloids have the ability to form metallic alloys.

Other physical properties and chemical properties of the metalloid elements are usually intermediate in nature.

In general, these elements are extremely fragile and, therefore, do not have many structural applications.

In alloys, catalysts, biological agents, glasses, flame retardants, optical storage and optoelectronics, semiconductors, pyrotechnics, and electronics, Metalloids and their compounds are used.

Where Are Metalloids On The Periodic Table?

Metalloids lie on either side of the dividing line between metals and nonmetals. This can be found, in varying configurations, on some periodic tables. Elements to the lower left of the line generally display increasing metallic behavior; elements to the upper right display increasing nonmetallic behavior. When presented as a regular stairstep, elements with the highest critical temperature for their groups (Li, Be, Al, Ge, Sb, Po) lie just below the line.

Metalloids are located between metals and nonmetals. The orange color on the Periodic table represents metalloids. They form a separating boundary between metals and nonmetals.

In other words, metalloids (semimetals) are located on the right side of the post-transition metals and on the left side of nonmetals. Also, we can say that metalloids are present in the diagonal region of the p block on the Periodic table.

Characteristic Properties of Metalloids

• Metalloids typically look like metals. However, these elements often behave like non-metals.
• Physically, metalloids are brittle, somewhat shiny substances that are usually solid at ambient temperatures.
• These elements usually have intermediate to fairly strong electrical conductivity
• Metalloids are known to have electronic band structures that are similar to semimetals or semiconductors.
• Chemically, these elements usually act as non-metals (in a relatively weak manner)
• These elements generally have intermediate energies of ionisation and values of electronegativity
• Metalloids are known to form amphoteric or weakly acidic oxides.
• These elements have the ability to form metallic alloys.
• Many of the other physical and chemical properties of metalloids, in essence, are intermediate.

Properties of Metalloids

Metalloids usually look like metals but behave largely like nonmetals. Physically, they are shiny, brittle solids with intermediate to relatively good electrical conductivity and the electronic band structure of a semimetal or semiconductor.

Chemically, they mostly behave as (weak) nonmetals, have intermediate ionization energies and electronegativity values, and amphoteric or weakly acidic oxides.

Most of their other physical and chemical properties are intermediate in nature.

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.

Examples of Metalloids on the Periodic Table

The six commonly recognised metalloids are boron, silicon, germanium, arsenic, antimony and tellurium.

Five elements are less frequently so classified: carbon, aluminium, selenium, polonium and astatine.

Commonly Recognised Metalloids

#1. Boron.

Boron is a versatile element that can be incorporated into a number of compounds. Borosilicate glass is extremely resistant to thermal shock.

Extreme changes in the temperature of objects containing borosilicate will not create any damage to the material, unlike other glass compositions, which would crack or shatter.

Because of their strength, boron filaments are used as light, high-strength materials for airplanes, golf clubs, and fishing rods.

Sodium tetraborate is widely used in fiberglass as insulation and also is employed in many detergents and cleaners.

#2. Silicon.

Silicon is a typical metalloid. It has luster like a metal but is brittle like a nonmetal. Silicon is used extensively in computer chips and other electronics because its electrical conductivity is in between that of a metal and a nonmetal.

It is a potent semiconductor, meaning it conducts electricity more efficiently at higher temperatures. Silicon compounds called silicates make up almost 90% of the earth’s crust, pure silicon is rare.

It is, however, relatively common in asteroids, moons, and cosmic dust. Silicates are frequently used in the manufacturing of cement, porcelain, and ceramics.

In the 21st century, silicon has had a massive influence on the world economy through its importance in the development of semiconductor electronics.

Pure silicon has been vital to the development of integrated circuit chips and transistors, both of which are crucial components of modern electronic devices, such as cell phones, televisions, and household appliances.

#3. Germanium.

Germanium is a shiny grey-white solid. It has a density of 5.323 g/cm3 and is hard and brittle. It is mostly unreactive at room temperature but is slowly attacked by hot concentrated sulfuric or nitric acid.

Germanium also reacts with molten caustic soda to yield sodium germanate Na2GeO3 and hydrogen gas. It melts at 938 °C.

It is also a good semiconductor and is rarely found in its pure elemental form on earth. Germanium frequently crystallizes into a diamond structure.

Germanium was predicted to exist by Dimitri Mendeleev years before it was actually discovered.

He was also able to predict many of its properties using his understanding of periodic trends and knowledge of other metalloids and nearby elements.

Like silicon, germanium is also critical to modern technology, although it is primarily used in different applications than its metalloid cousin.

Germanium is often used for infrared optics, solar energy, and numerous metal alloys.

#4. Arsenic.

Arsenic is a grey, metallic-looking solid. It has a density of 5.727 g/cm3 and is brittle, and moderately hard (more than aluminum; less than iron).

It is stable in dry air but develops a golden bronze patina in moist air, which blackens on further exposure.

Arsenic is attacked by nitric acid and concentrated sulfuric acid. It reacts with fused caustic soda to give the arsenate Na3AsO3 and hydrogen gas.

Arsenic sublimes at 615 °C. The vapor is lemon-yellow and smells like garlic. Arsenic only melts under a pressure of 38.6 atm, at 817 °C.

It readily forms covalent bonds with nonmetals. Arsenic has applications with regard to alloys, electronics, and pesticides/herbicides, but the use of arsenic for these applications is decreasing due to the toxicity of the metal.

Its effectiveness as an insecticide has led arsenic to be used as a wood preservative. It is classified as a Group-A carcinogen.

Despite its toxicity, very small quantities of arsenic are required for human metabolism, but the mechanism for this is unknown.

#5. Antimony.

Antimony is a silver-white solid with a blue tint and a brilliant luster. It has a density of 6.697 g/cm3 and is a brittle and moderately hard material that is a poor conductor of electricity.

It is stable in air and moisture at room temperature. Used with lead, antimony increases the hardness and strength of the mixture.

This material plays an important role in the fabrication of electronic and semiconductor devices.

About half of the antimony used industrially is employed in the production of batteries, bullets, alloys, cables, and plumbing equipment.

As is consistent with other metalloids, highly purified antimony can be used in semiconductor technologies.

It is found in nature at about ⅕ the abundance of Arsenic. Antimony has a similar atomic structure to arsenic as well, with three half-filled electron shells in the outermost shell.

It typically forms covalent bonds and is highly reactive with halogens, such as sulfur, and produces a brilliant blue flame when burned.

#6. Tellurium.

Tellurium is a silvery-white shiny solid. It has a density of 6.24 g/cm3, is brittle, and is the softest of the commonly recognized metalloids, being marginally harder than sulfur.

Large pieces of tellurium are stable in the air. The finely powdered form is oxidized by air in the presence of moisture.

Tellurium reacts with boiling water, or when freshly precipitated even at 50 °C, to give the dioxide and hydrogen.

Tellurium is a metalloid that exhibits a similar description to antimony. Tellurium is highly reactive with sulfur and selenium and shows a green-blue flame when burned.

Tellurium is industrially used as a steel additive and can be alloyed with aluminum, copper, lead, or tin.

Like antimony, tellurium can also strengthen other metals, but can also reduce corrosion when added to the aforementioned metals.

Additionally, tellurium serves as a strong semiconductor, particularly when exposed to light. In nature, most tellurium is found in coal, though trace amounts are found in some plants.

Examples of elements That are Irregularly Recognized as A Metalloids

#7. Polonium.

Polonium is a chemical element; it has symbol Po and atomic number 84.

A rare and highly radioactive metal (although sometimes classified as a metalloid) with no stable isotopes.

Polonium is a chalcogen and chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth.

Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 (with a half-life of 138 days) in uranium ores, as it is the penultimate daughter of natural uranium-238.

#8. Astatine.

Astatine is the 85th element of the periodic table with a symbol ‘At’.

It is a radioactive element and is said to be the most heavier among the halogens. This element exhibits similar chemical properties that of the element iodine.

The isotopes of astatine have a short life of about 8.1 hours, and some isotopes are said to be unstable. It has about seven isotopes. This element appears as a black solid with a metallic look.

It is considered as one of the rarest occurring natural element. About 2.36 × 10²⁵ grams of the earth’s crust comprises of astatine which measures about lesser than 1 gram. Astatine is mainly formed by the decay of thorium and uranium.

Examples of elements That are Less Commonly recognized as a Metalloids

#9. Selenium.

Selenium is a chemical element; it has the symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form.

It seldom occurs in this elemental state or as pure ore compounds in Earth’s crust. Selenium was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium (named for the Earth).

Selenium is found in metal sulfide ores, where it substitutes for sulfur. Commercially, selenium is produced as a byproduct in the refining of these ores.

Minerals that are pure selenide or selenate compounds are rare. The chief commercial uses for selenium today are glassmaking and pigments.

Selenium is a semiconductor and is used in photocells. Applications in electronics, once important, have been mostly replaced with silicon semiconductor devices.

Selenium is still used in a few types of DC power surge protectors and one type of fluorescent quantum dot.

 Examples of elements That are Rarely recognized as a Metalloids

#10. Carbon.

Carbon is a chemical element; it has symbol C and atomic number 6. Carbon makes up about 0.025 percent of Earth’s crust.

Carbon is the 15th most abundant element in the Earth’s crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen.

Carbon’s abundance, its unique diversity of organic compounds, and its unusual ability to form polymers at the temperatures commonly encountered on Earth, enables this element to serve as a common element of all known life.

It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.

#11. Aluminium.

Aluminium is the most abundant metal in the Earth’s crust (8.1%) but is rarely found uncombined in nature. It is usually found in minerals such as bauxite and cryolite.

These minerals are aluminium silicates. Most commercially produced aluminium is extracted by the Hall Héroult process.

Because of its chemical activity, aluminum never occurs in the metallic form in nature, but its compounds are present to a greater or lesser extent in almost all rocks, vegetation, and animals.

Aluminum is concentrated in the outer 16 km (10 miles) of Earth’s crust, of which it constitutes about 8 percent by weight; it is exceeded in amount only by oxygen and silicon.

The name aluminum is derived from the Latin word alumen, used to describe potash alum, or aluminum potassium sulfate, KAl(SO₄)₂∙12H₂O.

Applications of Metalloids

Typical metalloids have a metallic appearance, may be brittle and are only fair conductors of electricity.

They can form alloys with metals, and many of their other physical properties and chemical properties are intermediate between those of metallic and nonmetallic elements.

They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.

Metalloids and the compounds of metalloids are widely used as alloys, biological agents, flame retardants, catalysts, glasses, and optical storage media.

Metalloids are also known to have applications in optoelectronics, semiconductors, pyrotechnics, and electronics.

Alloys formed when combined with transition metals are extremely well-represented when it comes to the lighter metalloids. Boron has the ability to form intermetallic compounds.

This element also has the ability to form alloys with these MnB composition metals if the value of n is greater than 2.

In fact, ferroboron (which contains 15 per cent boron) is widely used in order to inject boron into steel.

Furthermore, nickel-boron alloys are used as ingredients in the engineering industry for welding alloys and case hardening compositions.

Silicon alloys of aluminium and iron are widely used in the construction and automotive industries. Germanium is known to form several alloys, especially the coinage metals in particular.

Medical Applications of Metalloids

Each and every one of the six elements that are widely known as metalloids are known to be either toxic, or to have medicinal and nutritional properties.

For example, compounds of antimony and arsenic are known to be especially toxic. However, boron, arsenic, and silicon are extremely important trace elements.

The four elements boron, arsenic, silicon, and antimony are known to have many medical uses. The remaining two elements (germanium and tellurium) are known to have great potential for medicinal applications.

Furthermore, boron is used in herbicides and also in insecticides. This element is an active trace element, which has several antiseptic, antiviral, and antifungal properties in the form of boric acid.

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