When SiO2 changes state, what forces/bonds are being overcome/broken?
$\ce{SiO_2}$ is a network covalent compound that has an extremely high melting and boiling point, because many silicon-oxygen bonds have to be broken in order for it to achieve the necessary freedom. To clarify, SiO2, which has a tetrahedra network lattice formation, shows that each silicon is actually bonded to 4 oxygens; each oxygen is bonded to 2 silicon. These excess bonds aside from the ones of SiO2 are broken.