why are metals good conductors of heat?

All solids are made up of atoms and molecules. However, metals contain free electrons which move randomly between the atoms and molecules.

One mechnism for conduction is atomic or molecular vibrations. When thermal energy is supplied to one end of a rod, the atoms or molecules at the hot end will vibrate vigrously. The particles will collide with neighbouring particles, causing them to vibrate as well. Thus, the kinetic energy is transferred from particle to particle.This is how the heat is transferred from the hot end of the rod to the cold end. This mechanism takes place in both metals and non-metals.

The other mechanism for conduction is free electron diffusion which only takes place in metals. When a metal rod is heated, the free electrons gain kinetic energy and they move faster. These electrons then diffuse or spread into the cooler parts of the rod. Thus, they collide with the particles in the cooler parts of the metal and transfer their kinetic energy to them.Thus, this explains why metals are capable of transferring thermal energy much faster than insulators.