Crystallography for 2nd Year Chemistry

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Questions and Answers

What is the Miller index notation for a basal pinacoid?

(0001)

How many faces does a hexagonal prism first order have?

Identify the Miller index notation for a dihexagonal prism.

(hk00)

What is the notation for a hexagonal bipyramid first order?

(h0hL) Signup and view all the answers

How many symmetry axes are there in the hexagonal system?

There are 7 symmetry axes in the hexagonal system. Signup and view all the answers

What is the Miller index notation for a hexagonal prism second order?

(1110) Signup and view all the answers

What are the conditions for the crystallographic elements in the hexagonal system?

The conditions are $a_1 = a_2 = a_3 \neq c$. Signup and view all the answers

How many mirror planes are present in the hexagonal system?

There are 7 mirror planes in the hexagonal system. Signup and view all the answers

What does a positive center indicate in the context of crystallography?

A positive center indicates the presence of a symmetry center in the crystal structure. Signup and view all the answers

What role do symmetry elements play in crystallography?

Symmetry elements help define the spatial arrangement of atoms in a crystal. Signup and view all the answers

What is the crystal form associated with the structure denoted as (hhhL) 12F?

Hexagonal bipyramid second order. Signup and view all the answers

Which crystal form corresponds to the notation (hk0L) 24F?

Dihexagonal bipyramid. Signup and view all the answers

What is the symmetry axis in the trigonal system mentioned in the context?

1∆c, 3a1, a2, a3. Signup and view all the answers

How many mirror planes are present in the system of symmetry described?

Three mirror planes (3m). Signup and view all the answers

What is the relationship between the axes a1, a2, and a3 in the described crystalographic elements?

a1 = a2 = a3 ≠ c. Signup and view all the answers

What is the relationship between angles α, β, and δ in the given crystal forms?

Angles α and β are both 90 degrees, while angle δ is 120 degrees. Signup and view all the answers

What type of crystal form is represented by the notation (hkwL)?

The notation (hkwL) represents a scalenohedron. Signup and view all the answers

Identify the symmetry elements in a cubic crystal system.

A cubic system has axes of symmetry: 3a, 3b, 3c, 4 at the face diagonals, and 6 through the edges. Signup and view all the answers

How many faces does a rhombohedron have and what is its Miller index notation?

A rhombohedron has 6 faces and is represented by the Miller index notation (h0hL). Signup and view all the answers

What is the significance of specifying angles in crystallography?

Specifying angles is crucial for understanding the geometric and symmetry properties of crystalline structures. Signup and view all the answers

What is the definition of a cube in crystallography and how many faces does it have?

A cube is a crystal form characterized by six equal square faces, and it has 6 faces. Signup and view all the answers

What is the Miller index notation for an octahedron and how many faces does it have?

The Miller index notation for an octahedron is (111), and it has 8 faces. Signup and view all the answers

What distinguishes the rhombododecahedron in terms of its faces and Miller index notation?

The rhombododecahedron has 12 faces and is denoted by the Miller index notation (110). Signup and view all the answers

Identify the number of faces for a trisoctahedron and provide its Miller index notation.

A trisoctahedron has 24 faces and is represented by the Miller index notation (hhL). Signup and view all the answers

What is the significance of the positive center in crystallography?

A positive center indicates symmetrical properties around a central point in the crystal structure. Signup and view all the answers

Study Notes

Crystallography

Presented by Dr. Wafaa Soliman, for second-year chemistry students
Covers hexagonal, trigonal, and cubic crystal systems

Hexagonal System

Symmetry Elements:
- 7 rotation axes (1c, 3a₁, a₂, a₃)
- 7 mirror planes (m)
- Positive center of symmetry (+ve)
Crystallographic Elements:
- a₁ = a₂ = a₃ ≠ c
- α = β = 90° ≠ δ = 120°
Crystal Forms:
- Basal pinacoid... (0001) 2F
- Hexagonal prism (first order)... (1010) 6F
- Hexagonal prism (second order)... (1110) 6F
- Dihexagonal prism... (hk00) 12F
- Hexagonal bipyramid (first order)... (h0hL) 12F
- Hexagonal bipyramid (second order)... (hhhL) 12F
- Dihexagonal bipyramid... (hk0L) 24F

Trigonal System

Symmetry Elements:
- 1 rotation axis (1c), 3 rotation axes (3a₁,a₂,a₃)
- 3 mirror planes (m)
- Positive center of symmetry (+ve)
Crystallographic Elements:
- a₁ = a₂ = a₃ ≠ c
- α = β = 90° ≠ δ = 120°
Crystal Forms:
- Ditrigonal prism... (hkw0) 6F
- Rhombohedron... (h0hL) 6F
- Scalenohedron... (hkwL) 12F

Cubic System

Symmetry Elements:
- 3 rotation axes (3a,b,c), 4 threefold axes (4) 6 (with planes)
- 9 mirror planes (m)
- Positive center of symmetry (+ve)
Crystallographic Elements:
- a = b = c
- α = β = δ = 90°
Crystal Forms:
- Cube (hexahedron)... (100) 6F
- Octahedron... (111) 8F
- Rhombododecahedron... (110) 12F
- Trisoctahedron... (hḥL) 24F
- Tetrahexahedron... (hk0) 24F
- Hexaoctahedron... (hkL) 48F

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Description

This quiz explores the hexagonal and trigonal crystal systems, including their symmetry elements and crystallographic characteristics. It's designed for second-year chemistry students to test their understanding of these structures in crystallography.