A material is not just a larger molecule. Once enormous numbers of atoms interact, collective modes, electronic bands, magnetic order and phase transitions become possible. This lab makes that change of scale visible while keeping each model explicit.
Switch between square and triangular order, then insert a vacancy or a schematic edge dislocation. Local coordination changes even though most of the lattice remains ordered.
Excite one normal mode of a one-dimensional monoatomic chain. The same spring coupling that binds neighboring masses produces a dispersion relation, so different wavelengths move and oscillate differently.
Use a one-dimensional tight-binding model. Increasing orbital overlap widens the band; changing the filling moves the Fermi edge. A partly filled band has nearby unoccupied states available in this idealized picture.
A finite two-dimensional Ising model provides a stripped-down demonstration: thermal agitation competes with neighbor alignment and an external field biases the collective state.
Landau theory compresses complex microscopic behavior into an order parameter. Above a critical point one minimum is preferred; below it, symmetry-related minima can appear.