Question

which governs the packing of particles in crystals?

Answer 1

In crystalline solids, the constituent particles (atoms, molecules, ions) are arranged in a regular pattern throughout the crystal lattice. This regular and repeating arrangement of points or particles in space is called as the crystal lattice structure. The spatial arrangement of the particles in a crystal is governed by two competing effects, namely, the interparticle Coulomb repulsion (between the ions of same charge or between the adjacent molecules) and the confinement electric field (between the oppositely charged ions or between the atoms of opposite polarity). The interparticle repulsion favors the formation of hexagonal structures, while the confinement electric field imposes the shape of the potential onto the lattice boundary.