Answer
It is not just the atoms in a material that determine its physical properties. For example, both hydrogen gas and water mostly contain H atoms, but have very different properties. Silicon in semiconductors is very purified, whereas in glass, silicon is bonded to oxygen. Furthermore, the silicon in semiconductors is crystalline, and in glass it is amorphous.
Physical properties depend on the arrangement and chemical bonding of the atoms, and depend on the presence of other atoms.
