X-ray Diffraction Flashcards
(25 cards)
What is the primary purpose of X-ray diffraction?
To understand the interaction of X-rays with crystals and gather information about atomic positions and molecular structures.
What are the two types of samples used in X-ray diffraction?
- Single crystal
- Powder
What is a single crystal’s typical size in X-ray diffraction?
0.1 x 0.1 x 0.1 mm
What is meant by ‘unit cell’ in crystallography?
An imaginary basic block that repeats in a crystal.
What are the three essential components needed to describe a crystal?
- Unit cell type and dimensions
- Atomic coordinates
- Space group symmetry
What are the dimensions of a unit cell typically measured in?
Ångstoms
What are the three lengths that define a unit cell?
- a
- b
- c
What is the significance of symmetry in a unit cell?
It allows us to determine the positions of all molecules in the unit cell by knowing just one molecule’s position.
Define Z and Z’ in the context of a unit cell.
- Z = Total number of molecules in the unit cell
- Z’ = Number of unique molecules in the unit cell
What does the term ‘space group’ refer to?
It summarizes all symmetry relationships in the unit cell.
What is the most commonly used X-ray wavelength in X-ray diffraction?
1.5406 Å
How do X-rays interact with matter?
X-rays scatter off of electrons.
What is Bragg’s law?
A reflection is only seen when λ = 2d sin(θ).
What does the variable ‘d’ represent in Bragg’s law?
Interplanar spacing (in Å)
What information can be obtained from measuring X-ray reflection angles?
You can work out cell dimensions.
What does the intensity of X-ray reflections indicate?
It reflects the positions and types of atoms in the unit cell.
What are Miller indices?
A numbering system to identify reflecting planes in a unit cell.
What is the main application of Single Crystal X-ray Diffraction (SX-XRD)?
Full crystal structure determination.
What is a polymorph in crystallography?
A particular crystalline form of a compound.
What is the key feature of a powder X-ray diffraction (PXRD) pattern?
It serves as a ‘fingerprint’ for a specific polymorph.
What happens during phase transformation in PXRD?
Different polymorphs interconvert, leading to changes in peak positions and heights.
What characterizes an amorphous material in PXRD?
Only short-range order with no clear Bragg diffraction.
What is the importance of crystallography in pharmaceuticals?
It is key to understanding the physicochemical properties of small molecules in the solid state.
Fill in the blank: A _______ is a mixture of left and right-handed enantiomers.
racemate
