Fan Lecture 4 Flashcards
What is structure factor?
A complex number that quantifies the contribution of each lattice point in a crystal to the scattering intensity observed in x-ray diffraction experiments. They are essential for determining the crystal structure and interpreting x-ray diffraction data.
What is atomic structure factor?
F(hkl) quantifies the contribution of each atom in a crystal lattice to the scattering of x-rays
- crucial for determining crystal structures and interpreting x-ray diffraction data
What is the overall structure factor of a crystal, knowing the content of the unit cell?
∑j fje^(2πi(hxj+kyj+lzj))
fj = scattering factor of atom j and a function of the electron density of the atom
What is the relationship between the structure factor F(hkl) and the reflection hkl?
Friedel’s law states that the structure factor Fhkl for a reflection hkl is equal to the complex conjugate of the structure factor Fhkl for the corresponding Friedel mate reflection.
What is the phase of F(hkl)?
represents the relative phase relationship between the scattered waves from different atoms within the crystal lattice.
varies from 0 to 2π radians
What is Friedel’s pair?
A pair of reflections in x-ray crystallography with indices hkl and -hkl. They have the same magnitude but opposite phases of the structure factor.
What is electron density? How does it relate to F(hkl)?
Electron density: spatial distribution of electrons within a crystal lattice; can be determined from the Fourier transform of the measured intensities of x-ray diffraction data.
Fhkl contains magnitude and phase information about the scattering x-rays by the crystal lattice. The squared magnitude is proportional to the electron density at the corresponding point in reciprocal space
Why does electron density function need to be calculated?
It provides information about the spatial distribution of electrons within a crystal lattice. It determines the position of atoms in the crystal structure, as well as chemical bonding and coordination.
