Book 27, Question 2
Why do the atoms in a crystal line up in a pattern?
Atoms and molecules attract each other, and they settle into the arrangement that uses the least energy, which is usually a tidy repeating pattern.
Imagine stacking boxes in a warehouse: neat rows fit better than a jumble. This repeating three-dimensional grid is called a lattice. Because the pattern repeats, a tiny piece of a crystal has the same arrangement as a huge one.