Crystal structures Flashcards
What is the definition of lattice points?
Points with identical surroundings
What is the definition of a motif?
Arrangement of atoms around a lattice point
Why is a particular unit cell used to describe a crystal?
Largest symmetry and smallest amount of lattice points
Why do hexagonal unit cells break the rules of why a unit cell is chosen?
Unit cell would be too big and the symmetry doesn’t match.
What is Weiss zone law and what does it tell us?
hu+vk+wl=0 tells us that a direction [uvw] lies on a lane (h,k,l).
How can you calculate where two planes intersect?
Calculate the dot product.
How do you work out the 3D packing density of a crystal?
Volume of space occupied by atoms (vol. of sphere x no. lattice points) / volume of unit cell
Why is there only 14 kinds of bravais lattices?
Not all types of unit cells are compatible with crystal systems and some combos have equivalent structures
How many types of unit cell are there?
4
What are the four types of unit cell?
Primative, body centered, face centered and base centered
How many lattice points does a primative unit cell have?
1
How many lattice points does a body centered unit cell have?
2
How many lattice points does a face centered unit cell have?
4
