Chapter 8

Question 1

Intermolecular forces

Answer 1

forces of attraction between molecules

Question 2

Order from strongest to weakest.

a) dipole-dipole
b) dispersion
c) hydrogen bond
d) dipole-induced-dipole
e) ion-dipole forces
f) ion-induced dipole

Answer 2

ion-dipole forces, hydrogen bond, dipole-dipole, ion-induced dipole, dipole-induced-dipole, dispersion

Question 3

True or False. All molecules have dispersion forces.

Answer 3

True

Question 4

True or False? The stronger the intermolecular force, the more kinteic energy is required to overcome this force, results in a higher boiling point.

Answer 4

True

Question 5

True or False. The greater the contact surface area, the less the net dispersion force.

Answer 5

False. The greater the contact surface area, the greater the net dispersion force.

Question 6

Which bonds can hydrogen bond with other molecules?

Answer 6

N-H
O-H
F-H

Question 7

Which of the following are directional and which are non-directional?

a) dispersion
b) dipole-dipole
c) hydrogen bonding
d) dipole-induced-dipole
e) ion-induced dipole

Answer 7

non-directional: 
a) dispersion
d) dipole-induced-dipole
e) ion-induced dipole
directional:
b) dipole-dipole
c) hydrogen bonding

Question 8

Surface tension

Answer 8

when water molecules are more attracted to each other than the air, forming a tough skin at the surface

Question 9

Capillary action

Answer 9

upward movement of water inside a capillary against the force of gravity

Question 10

Viscosity

Answer 10

the level of how much a liquid flows

ex) honey has high viscosity

Question 11

Vapour pressure

Answer 11

the weaker the intermolecular forces, the easier it is for the molecules to escape in the gas phase

Question 12

What is the relationship between a high intermolecular force and its surface tension, capillary action, viscosity, and vapour pressure?

Answer 12

high intermolecular force =
high surface tension
high capillary action
high viscosity
low vapour pressure

Question 13

Lattice points

Answer 13

corners of the unit cell

Question 14

Crystal lattice

Answer 14

group of identical unit cells

Question 15

Cubic unit cell

Answer 15

unit cell with edges of equal length and angles of 90 degrees

Question 16

Simple cubic characteristics

Answer 16

1/8 atom in each corner

8 atoms* 1/8 =1 full atom

Question 17

Calculate the mass of a single unit cell of polonium (Po) metal, which crystallizes in a simple cubic structure.

Answer 17

molar mass of Po= 209g/mol
Mass 1 atom Po = 209 / (6.0210^23)
= 3.4710^-22 g/ atom

Question 18

Body-centered cubic characteristics

Answer 18

1/8 atom in each corner

8 atoms* 1/8 +1 = 2 full atoms

Question 19

face-centered cubic characteristics

Answer 19

1/8 atom in each corner

8 atoms* 1/8 + 6*.5 = 4 full atoms

Question 20

Calculate the density of silver metal (in g/cm^3) if the edge length of its face-centered cubic unit cell is 407 pm.

Answer 20

molar mass of Ag = 107.9 g/mol
(4107.9) / 6.02210^23
=7.17*10^-22 g

407pm = 4.07*10^-8 cm

V= (4.0710^-8cm)^3
=6.7410^-23 cm^3
Density = m/v
=10.6 g/cm^3

Question 21

Gold metal crystallizes in a monoatomic face-centered cubic structure. The density of the metal is 19.3 gcm^-3. What is the length of the unit cell? What is its radius?

Answer 21

Au molar mass = 197.0 g/mol
4(197.0) / 6.022*10^23
= 1.309*10^-21 g
v=m/p
 =6.78*10^-23 cm^3

cube root of v = 4.09*10^-8 cm (length)

4r= square root of 2*l
r= 1.44*10^-8 cm or 144 pm

Question 22

Identify the predominant intermolecular force in each of the following substances:

a) CH4
b) H20

Answer 22

a) dispersion

b) hydrogen bonding

Question 23

Match the following properties of liquids to what they indicate about the relative strength (either strong or weak) of the intermolecular forces.

a) high boiling point
b) high vapour pressure
c) high surface tension
d) high viscosity

Answer 23

strong: high boiling point, high surface tension, high viscosity
weak: high vapour pressure

Question 24

When comparing two molecules, which intermolecular force is always associated with a higher boiling point?

Answer 24

hydrogen bonding

Question 25

Rank the following compounds from highest melting point to lowest melting point:
CH3Ch2OH
NaBr
SiC
CH3CH2CH3
KI

Answer 25

SiC, NaBr, KI, CH3CH2OH, CH3CH2CH3

• SiC is strongest due to being a network solid (covalent bonds)
• NaBr and KI are both ionic solids, but NaBr has a smaller radius
• the two organic molecules are molecular solids, but the one with OH is stronger due to hydrogen bonding

Question 26

List the order of solid types from strongest to weakest.

Answer 26

network solid (covalent), ionic solid (ionic), molecular solids (organic molecules)

Question 27

The radius of a single atom is 191 pm of an element X and a crystal of X has a unit cell that is simple cubic. Calculate the volume of the unit cell.

Answer 27

l=2r
= 2(191) = 382 pm = 3.82*10^-10 m

V= l^3
=5.57*10^-29 m^3

Question 28

Given that the density of KBr is 2.75 g/cm^3 and that the length of an edge of a unit cell is 659 pm, determine how many formula units of KBr there are in a unit cell.

Answer 28

v= m/p =43.3 cm^3*mol^-1

659 pm =6.59*10^-8 cm

v=l^3
= 2.86*10^-22 cm^3 per unit cell

43. 3/ 2.8610^-22 cm^3 per unit cell = 1.5110^23 unit cell*mol^-1
44. 02210^23 fromula unit mol^-1 / 1.5110^23 unit cellmol^-1

=3.98 or 4 formula unit cells