Here's why:

* Metals are typically shiny, malleable, ductile, and good conductors of heat and electricity.

* Nonmetals are generally dull, brittle, and poor conductors of heat and electricity.

* Metalloids have properties that fall somewhere in between metals and nonmetals. They can conduct electricity, but not as well as metals. They are also brittle, like nonmetals.

Silicon exhibits properties of both metals and nonmetals. It's a solid at room temperature, has a shiny appearance, and can conduct electricity (though not as well as metals). However, it is also brittle, like nonmetals.