Chemistry · Ch 6 — Solid State
Packing in Crystals
Packing in Crystals
A fruit stall displaying fruit in a closest-packed pile -- each fruit nestled into the depression formed by the fruits below it -- is a familiar, everyday picture of what this section formalises: how identical hard spheres (standing in for the atoms, ions or molecules of a crystal) can be packed together as closely as possible. Constituents of a crystal generally do pack this way, because closer packing maximises the attractive forces between them. …
What this figure shows. A photograph of a fruit stall display: rounded yellow-green fruits (sathukudi/orange-type citrus) stacked in tight rows, each fruit nestled in the depression between the fruits of the row below it -- the everyday closest-packed arrangement the text uses to introduce how identical hard spheres (atoms/ions/molecules) pack in a crystal. The vendor has stacked the fruit this way for a very physical reason -- nestling each fruit into the gap left by the layer below lets more fruit fit into the same display space, and holds the pile together more stably -- exactly the same close-packing logic that later, at the atomic scale, is shown to maximise the attractive …