Visual physics and mathematics/Crystal structures

A very little grain of salt File:A very little grain of salt.gif Each line represents a bond between two ions in a crystal of NaCl (sodium chloride = ordinary salt). Blue and green distinguish the two kinds of ions. It is a centered cubic crystal. Each Na+ ion is surrounded by 8 close neighbors Cl-. Likewise, each Cl- ion is surrounded by 8 close neighbors Na+. Two nearby ions always have opposite charges, because opposite charges attract each other while charges of the same sign repel each other. Crystal galaxies What would we see if we were small enough to be inside a crystal and see its atoms as stars, or if we looked up at the sky in a crystal galaxy? File:Cubic Galaxy.gif Cubic galaxy File:Diamond sky.gif Diamond sky A bright line of stars reveals that the line of vision (the line from the center of the eye to the center of the object) is in a plane of stars. These planes are like the faces of a precious stone: 500px The simple cubic structure The simple cubic structure is the simplest crystal structure: 500px File:Cubic lattice.gif The repetition of the same The simple cubic structure is a stack of cubes in the three directions of space. A crystal structure is obtained by the repetition of the same cell, not necessarily cubic, in one or more directions of space. A crystal structure can be in two dimensions: File:Plane hexagonal lattice 2.JPG A stack of identical spheres has the structure of a crystal. A frieze has the structure of a one-dimensional crystal: 640px The face-centered cubic structure File:Face-centered cubic lattice 5.gif This structure is obtained by repeating a face-centered cubic cell: File:Face centered cubic cell.gif The diamond structure File:Diamond structure 6.gif This structure is obtained by repeating the following cell: File:Diamond cell.gif Promenades inside a diamond: File:Travelling inside an infinite diamond.gif File:Promenade in a diamond.gif