CHEMISTRY OF ENGINEERING MATERIALS BASIC CONCEPTS OF CRYSTAL STRUCTURES

Question 1

has rigid and long-range order and its atoms, molecules, or ions occupy specific positions.

Answer 1

Crystalline solids

Question 2

observes absence of a well-define arrangement and long-range molecular order.

Answer 2

Amorphous solids

Question 3

is the basic structural (repeating) unit of a crystalline
solid.

Answer 3

unit cell

Question 4

is a crystal structure with atoms
located at each of the corners and the center of all the cube faces.
Some familiar metals having this crystal structure are copper,
aluminum, silver, and gold .

Answer 4

face-centered cubic (FCC)

Question 5

wherein each atom has
the same number of nearest-neighbor or touching atoms

Answer 5

the coordination number (for metals)

Question 6

which is the sum of the sphere
volumes of all atoms within a unit cell (assuming the atomic hard-
sphere model) divided by the unit cell volume.

Answer 6

atomic packing factor (APF)

Question 7

is another common metallic crystal
structure that also has a cubic unit cell with atoms located at all
eight corners and a single atom at the center of the cube.

Answer 7

body-centered cubic (BCC)

Question 8

The BCC crystal structure has_______coordination number.

Answer 8

8

Question 9

a metalloid or a semi-metal is the only simple-cubic element that has a relatively low atomic packing
factor.

Answer 9

Polonium,

Question 10

The top and bottom faces of the unit cellconsist six atoms that form regular hexagons and surround a single atom in the center. Between the top and bottom planes, there is another plane that provides three additional atoms to the unit cell. The atoms in this midplane have as nearest neighbors atoms in
both of the adjacent two planes.

Answer 10

the hexagonal
close-packed (HCP).