Visual physics and mathematics/Crystal structures
A very little grain of salt
[edit | edit source]
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
[edit | edit source]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?
Cubic galaxy
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:
The simple cubic structure
[edit | edit source]The simple cubic structure is the simplest crystal structure:
The repetition of the same
[edit | edit source]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:
A stack of identical spheres has the structure of a crystal.
A frieze has the structure of a one-dimensional crystal:
The face-centered cubic structure
[edit | edit source]
This structure is obtained by repeating a face-centered cubic cell:
The diamond structure
[edit | edit source]
This structure is obtained by repeating the following cell:
Promenades inside a diamond:
