Here's why:

* Silicon oxide is a general term that can refer to multiple compounds, but the most common one is silicon dioxide (SiO2), also known as silica.

* Silica forms a giant covalent structure, where silicon and oxygen atoms are linked together in a continuous network. This network extends in three dimensions, with each silicon atom bonded to four oxygen atoms and each oxygen atom bonded to two silicon atoms.

* Because of this continuous network, there are no distinct, individual SiO2 molecules.

Think of it like a giant diamond. Each carbon atom in a diamond is connected to four other carbon atoms, creating a vast network without any defined individual molecules.

In contrast, silicon monoxide (SiO), another silicon oxide, exists as individual molecules, but it is less common and less stable than silicon dioxide.