Diffraction Methods

Question 1

Diffraction

Answer 1

Photons interacting with electrons

Question 2

Mass Spectrometry

Answer 2

Measures the mass-to-charge ratio of ions, reveals how atoms are linked or arranged

Question 3

Spectroscopy

Answer 3

Used to investigate bonding and electronic transitions to characterise reactions

Question 4

Lattice

Answer 4

An infinite array of points in an identical environment. Involves translational symmetry

Question 5

Lattice Points

Answer 5

The identical points in a lattice

Question 6

Motif

Answer 6

The element of a lattice that is associated with a lattice point, i.e. the part that repeats

Question 7

Symmetry

Answer 7

An n-fold rotation axis of symmetry is aline of rotation about which 2π/n produces the identical position.
e.g. n=2, 2π/2=360°/2=180°

Question 8

Symmetry (e.g. 2-fold, 3-fold, 6-fold)

Answer 8

An n-fold rotation axis of symmetry is a line of rotation about which 2π/n produces the identical position.
e.g. n=2, 2π/2=360°/2=180°
Note: No 5-fold symmetry possible

Question 9

Centre of Symmetry

Answer 9

A point through which an inversion occurs

Question 10

Mirror Plane

Answer 10

A plane such that positions on one side of the plane are mirror images of the other side

Question 11

The Unit Cell

Answer 11

Smallest repeating unit, each corner contains 1/4 lattice point, 4 corners, (1/4*4)=1 lattice point
3 axial lengths: a,b,c
3 interaxial lengths,α,β,γ

Question 12

The Primitive Unit Cell

Answer 12

A single lattice point unit cell, has coordinates (0,0,0)

Question 13

P? I? F?

Answer 13

P=Primative (consists of one lattice point on each corner of the cube. Each atom at a lattice point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one atom (​1/8 × 8)).

I=Innenzentre/Body Centered (has one lattice point in the center of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell (​1/8 × 8 + 1)).

F=face centered (has lattice points on the faces of the cube, that each gives exactly one half contribution, in addition to the corner lattice points, giving a total of 4 lattice points per unit cell (​1/8 × 8 from the corners plus ​1⁄2 × 6 from the faces)).

Question 14

7 Crystal Systems

Answer 14

Triclinic: (a≠b≠c; α≠β≠γ≠90°)
Monoclinic: a≠b≠c; α=γ=90° β≠90°
Cubic: (a=b=c ; α=β=γ=90°)
Orthorhombic: (a≠b≠c; α=β=γ=90°)
Hexagonal: (a=b≠c; α=β=90° γ=120°)
Trigonal (	a=b=c; α=β=γ≠90°)
Tetragonal: (a=b≠c; α=β=γ=90°)

Question 15

32 Point Groups

Answer 15

32 different ways in which rotation axes , mirror planes, centres of symmetry, and rotary inversion axes can be used to describe the 7 crystal systems
e.g. Point group: 4mm

Question 16

Space Groups

Answer 16

230 Unique 3D structures (32 point groups + 14 Bravais lattices).
Designated by capital letter to identify lattice type: (Primative (P), Base (C), Body (I), Face (F))

Question 17

Screw Axis

Answer 17

A line that is simultaneously the axis of rotation and the line along which translation of a body occurs

Question 18

Close packed vs non-close packed contact

Answer 18

Close packed max contact = 6

Non-close packed max contact = 4

Question 19

Hexagonal Close Packed (HCP)

Answer 19

Primitive

Question 20

Cubic Close Packed (CCP)

Answer 20

Non-Primitive

Question 21

5 items to describe metal structures

Answer 21

Crystal system, Lattice Type, Unit cell dimensions and angles, the atomic contents of the units cell, coordinates of atoms that comprise a lattice motif

Question 22

Interstices

Answer 22

Gaps present in between even close packed molecules. Other molecules fill these gaps.
Can have tetrahedral coordination or octahedral coordination.
Tetrahedral = 1 pyramid, so 4
Octahedral = 2 pyramids attached by the base, so 8

Question 23

Miller Indices (hkl)

Answer 23

A set of parallel, equally spaced lattice planes are defined by Miller Indices (hkl) with
reference to a particular unit cell. hkl are integers that make intercepts of length a/h,
b/k, c/l on the x, y, and z axes respectively.

Question 24

d(khl)

Answer 24

The distance separating the planes (Interplanar spacing).

Determined by the dimensions of the unit cell and the associated Miller Indices