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The metalloids are elements that display characteristics of both metals and nonmetals. While there is no universally accepted list, the most frequently cited metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. Among these, boron possesses the smallest atomic radius.
Commonly recognized metalloids include:
Atomic radius increases down a group because each new row adds an additional energy level, pushing the outermost electrons farther from the nucleus. Across a period, however, the radius decreases. Although both protons and electrons increase, valence electrons occupy the same energy level, so the electron cloud does not expand substantially. The increasing nuclear charge pulls the electrons closer to the nucleus, resulting in a smaller atomic radius.
