The periodic table organizes elements into categories—metals, nonmetals, and metalloids—based on their shared properties. Metalloids occupy a transitional zone, exhibiting a blend of both metallic and nonmetallic traits. This intermediate classification often leads to confusion regarding their physical state at room temperature.
The Solid State of All Metalloids
No metalloid is liquid at standard room temperature and pressure; all of them are solids. The seven elements classified as metalloids—Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), and Astatine (At)—are all found in a solid state. This uniform physical state across the entire group is a reflection of their underlying atomic structure.
These elements possess high melting points, which prevents them from transitioning to a liquid state. For instance, Boron’s melting point is extremely high at about 2079°C, and even Tellurium, which has the lowest melting point of the common metalloids, still requires 449.5°C to liquefy. These temperatures are far above the range considered to be standard room temperature. The substantial energy required to disrupt their solid structure ensures they remain rigid and fixed.
Hybrid Properties and Crystalline Structure
The reason metalloids are consistently solid lies in their unique bonding and crystalline arrangement. Metalloids are distinguished by their ability to form extensive, three-dimensional network structures. This arrangement involves strong covalent bonds, where atoms share electron pairs in a fixed pattern.
Silicon and Germanium crystallize in a diamond-like structure, where each atom is covalently bonded to four neighbors. Breaking this vast network of interconnected atoms requires supplying a large amount of thermal energy. Arsenic and Antimony form puckered, layered structures, but the bonds within these sheets are still strong covalent links.
This rigid, continuous network structure accounts for their high melting points and their characteristic brittleness, a nonmetallic trait. Metalloids also exhibit a metallic-like luster and their electrical conductivity is intermediate, classifying them as semiconductors. This semi-conductivity is directly tied to the crystalline structure, where the electrons are more tightly bound than in metals but can still be excited to conduct electricity.
Contrasting Metalloids with Liquid Elements
The confusion about the metalloids’ state often stems from the existence of the few elements that are liquids at room temperature. Under standard conditions, only two elements are naturally found as liquids: the metal Mercury (Hg) and the nonmetal Bromine (Br).
Mercury and Bromine
Mercury is a liquid due to its unique electronic configuration, which results in weak metallic bonds between its atoms. This weakness requires minimal energy to overcome, allowing the atoms to flow freely at room temperature. Bromine, a halogen, is a liquid because it forms diatomic molecules (\(Br_2\)) held together by relatively weak intermolecular forces. These forces are easily broken by thermal energy at standard temperatures. The liquid state of these two elements is due to weak interatomic or intermolecular forces, a mechanism distinct from the strong covalent network bonding found in all metalloids.