Crystals and scattering

Question 1

Triclinic

Answer 1

All sides and all angles different
Identity or inversion centre only (1-fold)

Question 2

Monoclinic

Answer 2

All sides different, one unique angle
One 2-fold rotation axis or one mirror plane

Question 3

Orthorhombic

Answer 3

All side different, all angles 90 deg
Three perpendicular 2-fold rotation axes or one 2-fold axis of rotation and two mirror planes

Question 4

Point group

Answer 4

Group of symmetry related points.
Number means fold, m means mirrorplane, / is that they are paralell.

Question 5

Point group: Triclinic

Answer 5

-1

Question 6

Point groups: Monoclinic

Answer 6

2, m, 2/m

Question 7

Point groups: Orthorhombic

Answer 7

mmm, mm2, 222

Question 8

Symmetry related intensities

Answer 8

For a specific point there are intensities that are the same as it, related by symmetry (the point group)

Question 9

Point group: -1

Answer 9

Inversion :)
hkl = -h-k-l, -hkl = h-k-l, h-kl = -hk-l, hk-l = -h-kl

Question 10

Point goup: m

Answer 10

Mirror plane
4x2: hkl = -hk-l = -h-k-l = h-kl,
-h-kl = -hkl = hk-l = h-k-l

Question 11

Point group: 2

Answer 11

2-fold along one axis (probably y)

Question 12

Point group: 2/m

Answer 12

Parallell 2-fold and mirror plane

Question 13

Point froup: mmm

Answer 13

Mirror plane in x, y and z

Question 14

Point group: 222

Answer 14

2-fold along x, y and z

Question 15

Point group: mm2

Answer 15

Mirror in x, y and 2-fold in z

Question 16

Atomic scattering affected by vibration how?

Answer 16

Magnitude of atomic scattering factor falls off faster. Modelled by temperature (vibration) factor, B

Question 17

Mocaicity

Answer 17

Blocks of the crystal are not aligned with each other. The same S-vector will cross the Ewald sphere at different places. Broadening of diffraction spot.

Question 18

Phase diagram

Answer 18

Under saturated—> Saturated (saturation limit) –> Supersaturated (metastable, nucleation, precipitation)

Question 19

Aggregation

Answer 19

Assembly of proteins into amorphous clusters (unordered)

Question 20

CC1/2

Answer 20

half dataset correlation

Question 21

To reproduce the observed scattering we must take what into account?

Answer 21

To reproduce the observed scattering from a molecule, we must take atom vibrations into account when calculating structure factors.

Question 22

Increase in intesity, crystal compared to molecule?

Answer 22

Intensity is amplitude/structure factor squared. Use crystal size and unit cell size to calculate num of molecules, then square.

Question 23

Precipitate

Answer 23

Come out of solution

Question 24

Precipitant

Answer 24

Solution that makes something precipitate.