Chp.2 Crystallographic Structures

Question 1

Equation for density/Atomic Weight

Answer 1

p = (nA) / (VcNa)

Question 2

Crystalline

Answer 2

A solid material made up of atoms, ions or molecules set up in a periodic and repeating 3-Dimensional array

Question 3

Crystal Structure

Answer 3

The unit cell structure that the atoms will be spatially arranged in. (Cubic, Tetragonal, Hexagonal, rhombic, monoclinic, triclinic)

Question 4

Lattice

Answer 4

The regular geometrical arrangement of points in crystal space.

Question 5

Unit Cell

Answer 5

The basic structural unit of a crystal structure.

Question 6

Face Centered Cubic (FCC)

Answer 6

A crystal structure found in Aluminum, Copper, Gold, Lead, Nickel, Platinum, Silver, etc.

Structure: It has an atom in each corner and in the center of each face.

Question 7

Body Centered Cubic (BCC)

Answer 7

A common crystal structure found in Chromium, Iron (alpha), Molybdenum, Tantalum, Tungsten, etc.

Structure: It has an atom in each corner and in the middle of the cube.

Question 8

Hexagonal Close Packed (HCP)

Answer 8

A crystal structure found for some metals like Cadmium, Cobalt, Titanium (alpha), Zinc, etc.

Structure: It has an atom in each corner, the center of the top and bottom face and a triangle of atoms in the center of the shape forming an ABAB stacking of close packed planes.

Question 9

What is a Coordination #? What is it for SC,FCC,BCC,HCP?

Answer 9

The coordination number is the number of nearest neighbor or touching atoms. Metals will always have the same coordination number for instance.

Simple Cubic: 6, BCC: 8, FCC:12, HCP:12

Question 10

Atomic Packing Factor (APF)

Answer 10

The APF describes how efficiently atoms are packed together within a unit cell.

Metals typically have relatively large atomic packing factors to maximize the shielding provided by the free electron cloud.

APF = Vs / Vc
APF = (Volume of atoms in a unit cell) / (Total unit cell volume)

Question 11

What is Polymorphism?

Answer 11

Polymorphism is the ability for a material to exist in more than one crystal structure.

Question 12

What is Allotropy

Answer 12

Allotropy describes the possibility of the existence of two or more different crystal structures for a substance.
EX: Pure iron at room temp = BCC, At 912C it turns FCC

Question 13

What is a Cubic structures axial/interaxial?

Answer 13

Axial: a = b = c
Interaxial: alpha = beta = gamma=90deg

Question 14

What is a Hexagonal structures axial/interaxial?

Answer 14

Axial: a = b != c
Interaxial: alpha = beta=90deg = gamma=120deg

Question 15

What is a Tetragonal structures axial/interaxial?

Answer 15

Axial: a = b != c
Interaxial: alpha = Beta = Gamma=90deg

Question 16

What is a Rhombohedral (Trigonal) structures axial/interaxial?

Answer 16

Axial: a = b = c
Interaxial: alpha = beta = gamma!=90deg

Question 17

What is a Orthorhombic structures axial/interaxial?

Answer 17

Axial: a != b != c
Interaxial: alpha = Beta = Gamma=90deg

Question 18

What is a Monoclinic structures axial/interaxial?

Answer 18

Axial: a != b != c
Interaxial: alpha = gamma=90deg != beta

Question 19

What is a Triclinic structures axial/interaxial?

Answer 19

Axial: a != b != c
Interaxial: alpha != beta != gamma!=90deg

Question 20

What are the uvw direction indices?

Answer 20

These indices tell us the location of the location of the vectors head and tail.
u = n(x2-x1)/a
v = n(y2-y1)/b
w = n*(z2-z1)/c

Question 21

What is a single crystal?

Answer 21

A single crystal is a crystalline solid whose periodic and repeated arrangement of atoms is perfect and extends throughout the entire structure.