Boron is neither a metal nor a nonmetal; instead, it is classified as a metalloid or a semimetal. Boron is the chemical element with the symbol B and atomic number 5. Its molecular weight is 10.81 grams per mole, and its melting point is 2076 degrees Celsius.
Crystal boron is a dark substance with a hardness rivaling that of diamond. As a metalloid, boron's physical and chemical properties are between those of metals and nonmetals. It behaves as a nonmetal in reaction with sodium and a metal when combined with fluorine. Other chemical elements commonly classified as metalloids include silicon, germanium, arsenic, antimony and tellurium.