Why is antimony classified as a metalloid?

Antimony is classified as a metalloid because it possesses physical and chemical properties that are intermediate between those of typical metals and nonmetals.12

There is no single property that defines a metalloid, but antimony exhibits characteristics of both categories:

• Physical Properties: Like metals, antimony is a lustrous, solid element at room temperature. However, unlike typical ductile or malleable metals, it is very brittle and has a flaky texture. Its electrical conductivity is also intermediate, falling between that of metals and nonmetals.32
• Chemical Properties: Chemically, antimony behaves more like a nonmetal. It has an intermediate electronegativity, allowing it to gain, lose, or share electrons depending on the reaction. It is capable of displaying a range of positive and negative oxidation states and can form amphoteric oxides, which are capable of acting as either acids or bases.23

Because of these hybrid characteristics, antimony is grouped with other elements near the center of the periodic table's p-block that share these transitional traits.12