Solids Quiz

Question 1

Simple Cubic

coordination # 6

Answer 1

(8 corner atom) x (1/8 atom) = 1 atom / unit cell
volume unit cell: a ^3 = (2r)^3 = 8r^3
volume atom: 4/3π r^2
volume of total atoms: 4/3 (π) = 4.19 r^3
% occupied = volume of the total / volume of the unit cell x 100
% occupied = 4.19 r^3 / 8r^3 x 100 =

Question 2

Body Centered Cubic

coordination # 8

Answer 2

2 atoms / U.C.
volume u.c. = (4r)^3 / (sq. root 3) = 12.4r^3
volume of sphere (2 atoms / u.c. x 4/3 pie r^3) total = 8.37r^3
% occupied: 8.37r^3 / 12.4r^3 x 67.5 %

Question 3

Face Centered Cubic

coordination # 12

Answer 3

4 atoms / u.c.
volume of u.c. = (4r/sq. root 2)^3 = 22.8r^3
volume of total atoms: 4 atoms x 4/3 pie r^3 = 16.7r^3
% occupied = 16.7 r^3 / 22.8r^3 x 100 = 73.2 %

Question 4

example

Molybdem has an atomic radius of 136 pm and crystallizes in a body centered cubic system.
a. What is the length of the edge of a unit cell.
b. Calculate the density of molybdem.

(1pm = 1x10^-12 m) = 1.36 x 10^-10 m

Answer 4

a. (4r)^3 / (sq. root 3)
r = 1.36 x 10^-10
4 ( 1.36 x 10^-10 m)^3 / (sq. root 3) = 3.14 m (edge length)

BCC - 2 atoms/ u.c.

Question 5

crystaline solids

Answer 5

highly ordered arragemnet of particles

diomand, salt, graphite

Question 6

amorphous solids

Answer 6

disorder in their structures

rubber, plastic, glass