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Crystals > Lecture 11 > Flashcards

Lecture 11 Flashcards

1
Q

What are the three different types of symmetry elements in 3D?

A

point: centers of symmetry, mirror planes, and inversion axes

translational: glide planes and screw axes

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2
Q

How many different space groups are there for 3d?

A

230

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3
Q

How are bravais lattices grouped?

A

through their point group symmetries into seven crystal systems

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4
Q

Do P F I cubic lattices have the same point group symmetry?

A

yes

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5
Q

What is a crystal habit?

A

external shape

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6
Q

What are the centrosymmetric groups?

A
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7
Q

What does centrosymmetric mean?

A

the crystal posses an inversion center

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8
Q

What two shapes have the same point group symmetry? How is that determined?

A

cube and octahedron

you go through all the options (ex 4-fold 3-fold 2-fold) if they have the same # of each they’re the same

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9
Q

Does a tetrahedron have more or less symmetry than a cube? octahedron?

A

less, both are more

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10
Q

What is the characteristic of the cubic crystal? What are three crystal shapes in this category?

A

four triads

cube, octahedral, tetrad

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11
Q

What does it mean when two crystals belong to the same crystal class?

A

they have the same point group symmetry (ex cube and octahedron)– not necessarily the same shape

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12
Q

In 3D, what is a point group called?

A

a crystal class

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13
Q

How many different 3D crystal classes are there? 2d point groups?

A

3D- 32
2D- 10

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14
Q

What is the notation for an identity? inversion center? mirror plane? rotation axis n-fold? rotoinversion?

A
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15
Q

what does an 1 hat inversion look like? what is it also called?

A

inversion center

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16
Q

What does a 2 hat (m) look like? Also called?

A

2-fold rotoinversion

inversion diad

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17
Q

What does a 4 hat look like? also called?

A

4-fold rotoinversion

inversion tetrad

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18
Q

what does a 3 hat look like? also called?

A

3 fold rotoinversion

inversion triad

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19
Q

What does it for crystals to be in the same class?

A

their outer shapes have the same point group symmetries

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20
Q

What does point group symbol notation indicate?

A

the main symmetry elements present (not all, but most important)

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21
Q

what is the minimum symmetry for the cubic system? how do you identify with the symmetry notation?

A

4 triads

3 bar is the second number written or 3 for non-centro

22
Q

what is the minimum symmetry for the tetragonal system? which ones can it be? how do you identify?

A

1 inversion tetrad

Primitive, bcc (I)

4 is the first one listed in the notation

23
Q

what is the minimum for orthorhombic? what is the centro symmetric notation? non?

A

3 diads

PICF

centro; mmm
non centro: 222, mm2^P

24
Q

what is the minimum symmetry for trigonal?

A

1 rotation triad

trigonal=rhombohedral

R

25
Q

what is the minimum symmetry for hexagonal?

A

1 rotation hexad (6 in the phrase)

26
Q

By looking at the point symmetry notation, how do you kow if it’s centrosymmetric?

A

if it’s only one number and m’s

27
Q

what is the minimum qualification for monoclinic? triclinic?

A

1 inversion diad

none

28
Q

What does the order that the symmetry elements appear in the point group symbol depend on?

A

the crystal system

29
Q

what does /m mean? mm?

A

the mirror plane is perpendicular to the rotation axis

mm: mirror planes parallel to rotation axis

30
Q

what is the most common crystal class?

A

60% correspond to 2/m and m

31
Q

what is the most symmetric class?

A

m3m- cubic

32
Q

what does the addition of glide planes and screw axes make it called?

A

space groups

33
Q

How many Bravais lattices are there in 3D space

A

14

34
Q

What is body-centered in bravais notation

A

I

35
Q

what is face-center in bravais notation

A

F

36
Q

what is base-center in bravais notation

A

C

37
Q

What are the 14 bravais lattices for 3D space?

A

the 14 lattices are in 7 crystal systems

38
Q

What are the 7 crystal systems for the 14 bravais lattices?

A
  1. Cubic (3): simple cubic, BCC, FCC
  2. Orthorhombic (4): simple ortho, body-centered ortho, base-centered ortho, face-centered ortho
  3. tetragonal (2): simple tetrag, body-centered tetrag
  4. trigonal (1): rhombohedral
  5. hexagonal (1): hexagonal
  6. monoclinic (2): simple mono, base-centered mono
  7. triclinic (1): triclinic
39
Q

How are bravais lattices grouped?

A

by their point group symmetries into the seven crystal systems

40
Q

What are the different centrosymmetric crystal groups?

A
41
Q

What is the qualification to belong in the cubic crystal sysem?

A

four 3-fold axes

42
Q

What 3 3D shapes belong in the cubic system?

A
43
Q

What is the difference between crystal system and crystal class?

A

system– same qualifier
class- all the same point group symmetry

44
Q

In 2D, how many different crystallographic point groups are there? How many 3D point groups are there?

A

10- point groups

32- crystal classes

45
Q

What does inversion look like?

A
46
Q

What does inversion diad look like?

A
47
Q

What does inversion tetrad look like

A
48
Q

inversion triad

A
49
Q

what is the minimum symmetry for cubic, tetragonal, orthorhombic, trigonal, hexagonal, monoclinic and triclinic?

A
50
Q

How do you know the nomanclature order for different crystal classes?

A

the viewing directions listed on the chart

51
Q

what is the least common crystal class?

A

m3m

Crystals (11 decks)

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