Here's why:

* Free Electrons: Metals have a unique structure where their outer electrons are loosely bound and can move freely throughout the material. These "free electrons" are the key to their high conductivity.

* Thermal Conductivity: When heat is applied to a metal, these free electrons absorb energy and move around rapidly, transferring heat throughout the material.

* Electrical Conductivity: Similarly, when an electric field is applied, the free electrons flow easily, creating an electric current.

Nonmetals, on the other hand, have their electrons tightly bound to their atoms. This makes it difficult for them to move freely, resulting in low thermal and electrical conductivity.

Exceptions: While most nonmetals are poor conductors, there are some exceptions:

* Carbon (in the form of graphite) is an excellent conductor of electricity due to its unique layered structure that allows for free electron movement.

* Silicon and germanium are semiconductors, meaning they have conductivity between metals and nonmetals. They are crucial in electronics.