Xray Diffraction Flashcards
What is X Ray Diffraction
Shining X rays onto crystalline materials and observing scattered radiation
What does X Ray Diffraction tell us
Where the atoms are
How they are Connected to form molecules
How they pack to form crystals
To what extent they are vibrating
What is within a 3d molecular crystal
Unit Cell
Molecules
Atom Positions
What is a unit cell
it is an imaginary basic block that repeats which so that we can deal with something basic instead of every atom in a crystal.
What is a unit cell comprised of
an origin
Three length
Three Angles
What are the three lengths of the unit block denoted as
A B C
What are the three angles of the unit block denoted
alpha beta gamma
What unit is length measured in the unit cell
Angstrom (Å), unit of length, equal to 10−10 metre, or 0.1 nanometre
What are the two types of unit cell
orthorombic
monoclinic
describe an orthorombic unit cell
lengths do not have to be the same but all the angles are equal to 90 so creates a shoebox type unit cell
describe an monoclinic unit cell
lengths do not have to be the same but alpha and gamma angles are equal to 90 whereas beta is not equal to 90 creating a 3d rhombus
How do we denote an atoms position in a unit cell
they are defined via co-ordinates using the unit cell axis. Minimum value 0 maximum 1.
What co-ordinate corresponds to the axis
a = x b = y c = z
How are other molecules in the unit cell related
they are related by symmetry elements
why is it important to understand how molecules are related in the unit cell
knowing that molecules are related by symmetry elements means that we do not need to know the position of every molecule in the unit cell, we just need to find one provided we understand the symmetry relationships
Looking at big item takes time, looking at one molecule doesn’t if know symmetry know all
