Semimetals, sometimes referred to as metalloids, are chemical elements that occupy a transitional space on the periodic table. These elements possess properties that place them between the highly conductive metals and the insulating nonmetals. Their intermediate nature is important for understanding the structure of matter and bridging the distinct chemical and physical characteristics of the two major elemental classes.
The Hybrid Nature of Semimetals
The defining feature of this group is its variable electrical conductivity, which is the basis for their classification as semiconductors. Unlike typical metals, whose conductivity decreases as temperature rises, a semimetal’s ability to conduct electricity actually increases when heated. This temperature-dependent behavior allows for precise control over the flow of electrical current, a property that is absent in both pure metals and nonmetals.
Physically, semimetals exhibit a mixed aesthetic, appearing as shiny solids with a distinct metallic luster. However, their structural integrity is brittle; they will shatter rather than bend when subjected to stress. Chemically, they can display dual personalities, forming alloys when mixed with metals while also creating covalent compounds with nonmetals.
The unique electrical behavior can also be finely tuned through a process called doping, where tiny amounts of other elements are intentionally introduced to the structure. This controlled introduction of impurities can dramatically alter the semiconductor properties, making the material either electron-rich or electron-poor. This ability to manipulate their electrical response differentiates semimetals from the fixed conductive state of metals or the non-conductive state of insulators.
Location and Elements of the Semimetal Group
The location of the semimetals on the periodic table forms a boundary between the two main categories of elements. They are situated along a distinct, diagonal separation line, often called the “staircase” or “zigzag line.” This line physically separates the metals, which lie to the left, from the nonmetals, which are positioned to the right.
Seven elements are most commonly classified as semimetals. The scientific consensus is strong for the first six, but the inclusion of Polonium is sometimes debated due to its high radioactivity and metallic characteristics. These elements are:
- Boron (B)
- Silicon (Si)
- Germanium (Ge)
- Arsenic (As)
- Antimony (Sb)
- Tellurium (Te)
- Polonium (Po)
The elements span across several groups, starting with Boron in Group 13 and continuing through to Polonium in Group 16. This diagonal arrangement highlights how the metallic character of elements diminishes and the nonmetallic character increases as one moves across a period.
Essential Technological Applications
The controllable conductivity of semimetals makes them crucial in nearly all modern electronic devices. Silicon, the most well-known semimetal, forms the foundation of the microelectronics industry, providing the base material for integrated circuits, transistors, and microprocessors. Germanium is often paired with silicon in high-speed circuits and utilized in solar cells due to its efficiency in converting light into electrical energy.
Beyond electronics, other semimetals serve unique industrial roles that leverage their specific properties. Boron is valued for its high melting point and is used to strengthen materials, notably in the production of durable borosilicate glass and high-performance ceramics. Antimony is frequently introduced into metal mixtures to create alloys that are harder and stronger, and its compounds are used as effective flame retardants in plastics and textiles.
Materials science is exploring new applications for a class of compounds called topological semimetals, which exhibit unique quantum properties. These materials are being investigated for use in next-generation computing technologies, such as spintronics. Spintronics could process data using less energy than traditional charge-based electronics.