The metalloids or semimetals are elements with properties intermediate between the metals and nonmetals. Each metalloid element takes many forms, but has at least one shiny, metallic-looking allotrope. Solids are brittle, with nonmetal chemical properties. While metalloids are neither good electrical nor thermal conductors, they make excellent semiconductors and form amphoteric oxides. Take a closer look at the list of metalloids, their properties, and uses.
Key Takeaways: Metalloids
- Metalloids show properties of both metals and nonmetals.
- Most are brittle, metallic-looking solids.
- Metalloids are good semiconductors and form amphoteric oxides.
- There are 6–8 elements commonly classified as metalloids.
- Uses include semiconductors, flame retardants, and catalysts.
List of Metalloids
This is a list of the metalloid elements in order of increasing atomic number. Element 117 (tennessine) may also be a metalloid.
| Atomic Number | Symbol | Name | Notes |
|---|---|---|---|
| 5 | B | Boron | Essential in plant biology |
| 14 | Si | Silicon | Primary semiconductor material |
| 32 | Ge | Germanium | Used in transistors and optics |
| 33 | As | Arsenic | Poisonous, used in alloys and semis |
| 51 | Sb | Antimony | Flame retardants, alloys |
| 52 | Te | Tellurium | Used in solar cells and metallurgy |
| 84 | Po | Polonium | Radioactive, rare, metalloid-like |
| 117 | Ts | Tennessine | Predicted to be a metalloid (unstable) |
Note there is some debate about metalloid classification:
- Astatine (At) is sometimes classified as a metalloid.
- Tennessine (Ts) may be a metalloid based on predicted behavior.
Location of the Metalloids on the Periodic Table
The metalloids divide the periodic table along a zig-zag line between the metals on the left and the nonmetals on the right. Usually, the line runs under boron, germanium, antimony, and polonium. But, chemists disagree somewhat on metalloid classification. The line is more of a guide than a rule.
Metalloid Properties
Metalloids share the following properties:
- Appearance: Metalloids are either dull or shiny.
- Phase: Most metalloids are solid at room temperature and pressure.
- Thermal Conductivity: These elements conduct heat, but not as well as the metals.
- Electrical Conductivity: Metalloids are good semiconductors. They conduct electricity better than nonmetals but not as well as metals.
- Brittleness: They are typically brittle like nonmetals and break easily. Some metalloids are malleable and ductile.
- Chemical Behavior: Metalloids typically behave as nonmetals in chemical reactions. Atoms of metalloid elements both gain and lose electrons in reactions.
- Electronegativity: The have electronegativity values between those of metals and nonmetals.
- Ionization Energy: Their ionization energies are between those of metals and nonmetals.
- Alloying Behavior: They form alloys with metals.
Metalloids display widely variable melting points, boiling points, and density values.
Comparison of Metals, Metalloids, and Nonmetals
| Property | Metals | Metalloids | Nonmetals |
|---|---|---|---|
| Luster | Shiny | Shiny or dull | Dull |
| Conductivity | High | Moderate (semicon.) | Poor |
| Malleability | Malleable | Brittle | Brittle |
| Electronegativity | Low | Intermediate | High |
| Oxide Type | Basic | Amphoteric/acidic | Acidic |
| Electron Behavior | Lose electrons | Gain/lose electrons | Gain electrons |
Metalloid Uses
The metalloids have many uses:
- Semiconductors: Silicon and germanium are essential in microchips, solar panels, and transistors.
- Alloys: Arsenic and antimony improve the strength and hardness of lead alloys.
- Catalysts: Boron compounds catalyze organic reactions.
- Flame Retardants: Antimony trioxide is used in textiles and plastics.
- Glass and Ceramics: Boron and tellurium are used to improve thermal and optical properties.
- Biological Applications: Boron is a micronutrient in plants. Arsenic has medical and antimicrobial uses.
- Pyrotechnics: Boron gives green colors in fireworks; antimony enhances sparkle.
Frequently Asked Questions (FAQs)
Q: Are metalloids metals or nonmetals?
A: They are neither. Metalloids have properties of both but are classified as a separate category.
Q: How many metalloids are there?
A: Six are widely accepted. Some classifications include up to eight.
Q: What is the most important metalloid?
A: Silicon, due to its critical role in electronics and computing.
Q: Can metalloids conduct electricity?
A: Yes, they are semiconductors—better than nonmetals but worse than metals.
Q: Is carbon a metalloid?
A: No, carbon is a nonmetal, although it forms some metallic-looking allotropes (e.g., graphite).
References
- Brady, J.E.; Humiston, G.E.; Heikkinen, H. (1980). “Chemistry of the Representative Elements: Part II, The Metalloids and Nonmetals”. in General Chemistry: Principles and Structure (2nd ed.). John Wiley & Sons: New York. ISBN 0-471-06315-0.
- Chedd, G. (1969). Half-Way Elements: The Technology of Metalloids. Doubleday, New York.
- Goldsmith, R.H. (1982). “Metalloids”. Journal of Chemical Education. 59(6): 526–527. doi:10.1021/ed059p526
- Greenwood, N.N.; Earnshaw, A. (2002). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-7506-3365-4.
- Vernon, R.E. (2013). “Which Elements are Metalloids?”. Journal of Chemical Education. 90(12): 1703–1707. doi:10.1021/ed3008457