Macroscopically, a solid substance is one that retains its shape and size without the help of a container. On the atomic scale, a solid is a collection of particles (atoms, ions or molecules) for which their net attractive potential energy is greater than their kinetic energy. This leads to particle packing through interatomic/intermolecular forces or by bond formation. The resulting structures will have a certain degree of order, that can be ideally complete (perfect crystalline solids), totally absent (amorphous solids) or somewhere in between these two limiting cases.