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Fine antimony on white background. Image Credit: Shutterstock.com/Bjoern Wylezich

6 Properties of Metalloids

Learn more about the key properties of these elements.

Xomety X
By Team Xometry
August 8, 2022
 6 min read
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Metalloids are a class of elements that have properties of both metals and nonmetals. They fall between metals and nonmetals on the periodic table. The definition of metalloids, as well as the number of elements that fall into the metalloids group, is often argued by scientists. Boron, silicon, germanium, arsenic, tellurium, and antimony are all generally accepted as being metalloid elements, and as such, will be the focus of this article. However, while polonium, astatine, and bismuth are also sometimes classified as metalloids, they will not be discussed.

This article will describe the six most important properties of metalloids and list some key metalloids characteristics.

1. Metalloids Are Solids

All metalloids are solid at room temperature and have relatively high melting points. The melting points of the metalloids are listed in Table 1 below:

Table 1. Melting Temperatures of Metalloids
ElementMelting Temperature (°C)
Element

Boron

Melting Temperature (°C)

2079

Element

Silicon

Melting Temperature (°C)

1410

Element

Germanium

Melting Temperature (°C)

938.3

Element

Arsenic

Melting Temperature (°C)

817

Element

Tellurium

Melting Temperature (°C)

449.5

Element

Antimony

Melting Temperature (°C)

631

2. Metalloids Have a Metallic Luster and Appear to be Metals

Metalloids have the physical appearance of metals. Their metallic/reflective surface makes it immediately obvious why the name "metalloid" fits these elements. Table 2 below illustrates the visible surface characteristics of metalloids:

Table 2. Physical Appearance of Metalloids
ElementsImage
Elements

Boron

Image

Boron crystal. Image Credit: Shutterstock.com/Bjoern Wylezich

Elements

Silicon

Image

High purity polycrystalline. Image Credit: Shutterstock.com/Bjoern Wylezich

Elements

Germanium

Image

Fine germanium. Image Credit: Shutterstock.com/Bjoern Wylezich

Elements

Arsenic

Image

Arsenic. Image Credit: Shutterstock.com/Bjoern Wylezich

Elements

Tellurium

Image

Fine tellurium. Image Credit: Shutterstock.com/Bjoern Wylezich

Elements

Antimony

Image

Antimony. Image Credit: Shutterstock.com/Bjoern Wylezich

3. Metalloids Are Brittle and Easily Broken

Metalloids cannot be formed using the cold-forming techniques normally used for metals because they are very brittle. Metalloids will tend to fail due to brittle fracture or crumbling. 

4. Metalloids Have the Ability To Conduct Electricity, but Not As Well as Metals

Metalloids can be manipulated to behave as either conductors or insulators. This semiconducting behavior is what makes some, if not all, metalloids so useful in controlling complex electronic circuits. Metalloids are modified into semiconductors useful for a wide range of circumstances by a process called "doping." Doping is the process of adding impurities to alter the properties of intrinsic semiconductors, like metalloids. Despite their valuable semiconducting capabilities, metalloids are still poor conductors of electricity compared to metals.

5. Metalloids Behave More Like Nonmetals in That They Easily Form Anions, Have Multiple Oxidation States, and Form Covalent Bonds

The oxidation state of an element refers to the number of electrons an atom either gains or loses to bond chemically with another atom. In the case of metalloids, single covalent bonds are more common. A covalent bond refers to the situation where a pair of atoms share one electron. The oxidation states of the metalloid elements are listed in Table 3 below: 

Table 3. Metalloids’ Oxidation States
ElementsOxidation States
Elements

Oxidation States

Positive

Negative

Elements

Boron

Oxidation States

+3, +2, +1

-5, -1

Elements

Silicon

Oxidation States

+4, 0

-4

Elements

Germanium

Oxidation States

+2, +4

Elements

Arsenic

Oxidation States

+3, +5

-3

Elements

Tellurium

Oxidation States

+4, +6

-2

Elements

Antimony

Oxidation States

+3, +5

-3

Table Credit: Material-Properties.org

6. Metalloids' Ionization Energies and Electronegativities Are In Between the Values of Metals and Nonmetals

“Ionization energy” refers to the amount of energy that is required to strip an electron from a neutral atom to form an ion. The first ionization energy is the energy required to strip off the first electron - this is the easiest electron to strip. Electronegativity refers to how easily an atom will attract elements when forming a chemical bond. The higher the number, the stronger the attraction. Therefore, the higher the value for electronegativity, the more likely it is that the element will attract electrons. If two elements with similar electronegativities bond, they will form a pure covalent bond that equally shares the electrons. However, if elements have different electronegativities, the resulting molecule will be polarized. This is because the electrons in the bond will be attracted more to the stronger electronegativity element. The metalloids listed in Table 4 below have ionization energies and electronegativities as shown:

Table 4. Metalloids’ 1st Ionization Energies and Electronegativities
Elements1st Ionization Energy (eV)Electronegativity (Pauling Scale)
Elements

Boron

1st Ionization Energy (eV)

8.298

Electronegativity (Pauling Scale)

2.04

Elements

Silicon

1st Ionization Energy (eV)

8.1517 

Electronegativity (Pauling Scale)

1.9

Elements

Germanium

1st Ionization Energy (eV)

7.9

Electronegativity (Pauling Scale)

2.01

Elements

Arsenic

1st Ionization Energy (eV)

9.8152

Electronegativity (Pauling Scale)

2.18

Elements

Tellurium

1st Ionization Energy (eV)

9.0096

Electronegativity (Pauling Scale)

2.1

Elements

Antimony

1st Ionization Energy (eV)

8.64

Electronegativity (Pauling Scale)

2.05

What Distinguishes Metalloids?

The key distinguishing properties of metalloids are that they have characteristics of both metals and nonmetals. Their ability to act as semiconductors is an important and unique feature of some metalloids. This makes metalloids indispensable in an era when electronic circuits are everywhere.

Which Property Is the Most Useful for Identifying a Metalloid?

Most metalloids can be visually identified by their metallic appearance. Identifying metalloids by their chemical attributes is generally more difficult, as there are no properties of metalloids that make them stand out distinctly enough from other elements.

What Elements Are Commonly Referred to As Metalloids?

The elements that are commonly referred to as metalloids are listed in Table 5, along with brief descriptions and a few typical applications:

For more information, see our guide on the Elements of Metalloids.

Table 5. Metalloids: Descriptions and Typical Applications
ElementDescriptionApplication
Element

Boron

Description

An allotropic semimetal that is extremely hard and heat resistant. Has an atomic number of 5.

Application

Used with silicon to make thermal shock-resistant glass.

Element

Silicon

Description

A gray and shiny semiconductive metal. It has high melting (1,410 °C) and boiling points (3,265 °C). Has an atomic number of 14.

Application

Commonly used for semiconductors.

Element

Germanium

Description

Is hard and brittle in its elemental form. Has an atomic number of 32.

Application

Less commonly used for semiconductors.

Element

Arsenic

Description

A steel-gray semimetal known for being poisonous. It has an atomic number of 33.

Application

Often used as an insecticide.

Element

Tellurium

Description

Brittle in its elemental form. It is a chalcogen, along with selenium and sulfur. It has an atomic number of 52.

Application

Used as a steel additive to improve machinability.

Element

Antimony

Description

A hard, and brittle semimetal with an atomic number of 51.

Application

Used to color paints;  often alloyed with lead.

What Is the Composition of Metalloids?

Metalloids are fundamental elements, just like all the other elements on the periodic table. Like all elements, they are composed of protons, neutrons, and electrons.

For more information, see our metalloid guide.

What Is a Metalloid's Most Useful Property?

Metalloids’ most useful property is their semiconducting behavior. They are widely used in electronics. The conductivity of semiconducting metalloids can be enhanced using a technique called doping. Doping consists of the addition of small amounts of impurities to the base semiconductor to change its charge-carrying properties in desirable ways. Additionally, metalloids are often used as alloying elements. 

Is Metalloid Brittle or Malleable?

Metalloids are brittle. This means that when deformed, they tend to crack instead of deforming elastically or plastically. Therefore, they cannot be used for structural applications. Metalloids tend to be used as alloying elements in metals, or as semiconductors in electrical devices instead.

How Do You Categorize a Metalloid?

Metalloids are categorized neither as metals nor as nonmetals. This is because they have properties intermediate between those of metals and non-metals. They exist in the space between elements that are definitely metals and those that are definitely nonmetals, because of their unique combination of the characteristics of both of those other groups.

How Can the Electronic Configuration of a Metalloid Be Determined?

The electron configuration is determined by the number of electrons in an element. Electrons will fill the orbitals in a predictable manner and always occupy the lowest energy orbital available. Electron configuration refers to the way in which electrons are arranged around the nucleus of an atom. 

What Is the Difference Between Metal and Nonmetal?

Some differences between metals and nonmetals are shown in table 6 below:

Table 6. Comparison of Metals and Nonmetals 
PropertiesMetalsNonmetals
Properties

Electrical Conductivity

Metals

Generally conductive

Nonmetals

Nonconductive; behave as insulators

Properties

Mechanical Properties

Metals

Can be hard or soft, ductile or brittle.

Nonmetals

Generally brittle and hard, not suitable for mechanical applications

Properties

Thermal Conductivity

Metals

Metals are more thermally conductive than nonmetals

Nonmetals

Nonmetals are not very thermally conductive

Properties

Form

Metals

Most metals are solids at room temperature (barring a few exceptions like gallium or mercury)

Nonmetals

Nonmetals can be in the form of gasses (e.g., hydrogen), liquids (e.g.,  bromine),  or solids (e.g.,  carbon)

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Summary

This article reviewed 6 key properties of metalloids and explained what these elements are and how they are used.

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Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.