Lecture one and two

Question 1

What is a lattice?

Answer 1

A Lattice is a pattern of repeating points along which crystal unit cells can be arranged

Question 2

What is the word to describe a set of repeating points along which a Crystal unit cell is placed

Answer 2

A lattice

Question 3

What is a primitive unit cell

Answer 3

The unit cell which Only has lattice points in each corner

Question 4

What is a Unit cell that only has lattice points in each corner called

Answer 4

A primitive unit cell

Question 5

What is the atomic arrangement associated with a unit cell called

Answer 5

A motif

Question 6

What is a motif?

Answer 6

The atomic arrangement associated with a unit cell

Question 7

What components are required to describe the structure of an atomic arrangement

Answer 7

A lattice and a motif

Question 8

What happens when you add a motif to a lattice

Answer 8

You get the whole atomic structure

Question 9

How many arrangements of lattice points are possible?

Answer 9

Only five

Question 10

What are the five possible arrangements of lattice points called

Answer 10

The primitive square lattice, the regular primitive lattice, The oblique P lattice, The rectangular centred lattice, and the hexagonal P lattice

Question 11

What is a primitive square lattice

Answer 11

The sides are of equal length and the angle between the sides is 90°

Question 12

What is a regular Primitive lattice

Answer 12

Besides can be of any length but the angle between the sides must always be 90°

Question 13

What is an oblique p lattice

Answer 13

The sides can be of any length and it can have any angle between the sides except 90°

Question 14

What is a rectangular centred lattice

Answer 14

It is the same as a regular primitive lattice except that it also has a lattice point in its centre

Question 15

What is a hexagonal P lattice

Answer 15

A special form of the oblique P lattice with an angle between the sides of 60°

Question 16

What is a symmetry element in a lattice

Answer 16

An element that when applied to a point on a lattice will restore the lattice to it’s original position

Question 17

What fold of rotation symmetry can a lattice not have and why

Answer 17

Five-fold symmetry because a planar space cannot be filled with regular pentagons

Question 18

What are the 4 symmetry elements of a lattice

Answer 18

Translation symmetry, mirror plane symmetry, glide Plane symmetry, and rotation symmetry

Question 19

What is translation symmetry

Answer 19

Symmetry such that a point can be moved in a straight direction along the lattice maintaining its structure

Question 20

What is mirror plane symmetry

Answer 20

Symmetry such that an element can be reflected over the line and maintain its structure

Question 21

What is glide plane symmetry

Answer 21

Mirror Symmetry and translation symmetry in half steps form glide plane symmetry

Question 22

What is rotation symmetry

Answer 22

Symmetry such that an object can be rotated around an axis a regular number of times maintaining its structure

Question 23

What is a triclinic system

Answer 23

A system where the three axes are not equal in length and the angles between the axes are not equal to each other

Question 24

What is a monoclinic system

Answer 24

A system where the axes are not equal in length and two of the angles between the axes are 90° while the third angle is greater than 90°

Question 25

What is an orthorhombic system

Answer 25

A system where the three axes are not equal in length but all of the angles between the axes are equal to 90°

Question 26

What is a Tetragonal system

Answer 26

A system Where two of the axes are equal in length and all of the angles between the axes are 90°

Question 27

What is a hexagonal system

Answer 27

A system with four axes such that three of the axes are of equal length and are spaced at 120° angles, Perpendicular to the fourth irregular axis

Question 28

What is an isometric system

Answer 28

A system such that the three axes are of equal length and at 90° to each other

Question 29

What are the three rules which assist in choosing the best definition of a unit cell

Answer 29

One the edges of the unit cell should coincide with the symmetry of the lattice. Two the edges of the unit cell should be related by the symmetry of the lattice. Three the smallest possible cell which contains all the elements should be chosen

Question 30

What are Vectorial properties

Answer 30

Properties of a crystal which depend on direction within the crystal

Question 31

Which coordinate axis does axis “a” Correspond with

Answer 31

The x axis

Question 32

Which coordinate axis does axis “b” Correspond with

Answer 32

The Y axis

Question 33

Which coordinate axis does axis “c” Correspond with

Answer 33

The Z axis

Question 34

Which two axes does angle alpha define

Answer 34

B and c

Question 35

Which two axes does angle beta define

Answer 35

A and c

Question 36

Which two axes does angle gamma define

Answer 36

A and B

Question 37

How many crystal systems are there

Answer 37

There are six crystal systems

Question 38

What are the six Crystal systems

Answer 38

Cubic or isometric system, tetragonal system, orthorhombic system, monoclinic system, triclinic system, and the trigonal or hexagonal system

Question 39

Do the 6 Crystal systems describe All of the variations of 3-D crystal arrangements?

Answer 39

No the six systems can also be primitive, face centred, or body centred, Such that the arrangement of lattice points upholds the rules of symmetry

Question 40

How many possible 3-D arrangements of lattices are there And what is this set called

Answer 40

14 Called the bravais lattices

Question 41

What are the two types of spaces between neighbouring spheres in stacked sheets called

Answer 41

Tetrahedral sites and octahedral sites

Question 42

What is a tetrahedral site

Answer 42

A space bound by four spheres where the centre of each of these spheres is joined to form a tetrahedron

Question 43

What is an octahedral site

Answer 43

A Space bound by six spheres where the centre of the spheres are joined to form an octahedron

Question 44

What is hexagonal close packing

Answer 44

An arrangement whereby the layers are repeated in an A.B. A.B. A.B. pattern

Question 45

What is cubic close packing

Answer 45

An arrangement where the layers I repeated in an A.B.C.A.B.C pattern

Question 46

What is body centred cubic packing

Answer 46

A way of stacking spheres such that the atoms only have eight neighbours

Question 47

What are the three types of Crystal symmetry

Answer 47

Planar symmetry, Axial symmetry, centres of symmetry

Question 48

What is planar symmetry

Answer 48

A plane of symmetry that divides a crystal into two similar halves such that one half is the mirror image of the other

Question 49

What is axial symmetry

Answer 49

A type of symmetry where a Crystal can be rotated around an axis in intervals where the original crystal shape and orientation is repeated

Question 50

What are the four types of Axial symmetry

Answer 50

A diad axis (two-fold) a triad axis (thee-fold) a tetrad axis (four-fold) and a hexad axis (six-fold)

Question 51

What are crystal centres of symmetry

Answer 51

An element of symmetry that is recognized when all like faces or edges of a crystal are arranged in pairs on opposite sides of a central point

Question 52

What are Miller indices

Answer 52

A system of defining Crystal faces, Developed by WH Miller in the 19th century which uses the unit cell of the Crystal and three points which cut the axes of that cell into ratios. Only the denominator of the ratios are displayed in a set enclosed by brackets.

Question 53

What Is a vector

Answer 53

A line which has both magnitude and direction