Transcript I. Intermolecular Forces - Greer Middle College || Building the Future

States of
Matter
States of Matter
Solid
Liquid
Gas
What causes the
differences in
solids, liquids, and
gases?
Kinetic Molecular
Theory

Describes behavior of matter in terms of
particles in motion.
 Makes assumptions of gas particles:
• separated by empty space
• particles are not attracted to each other
• are in constant, random motion
• collisions are elastic
• kinetic energy determined by mass & velocity
KE = ½
2
mv
Liquids & Solids
I. Intermolecular Forces
(between molecules)
(Ch. 6, p.189-193)
C. Johannesson
A. Definition of
Intermolecular Forces
 Attractive
forces between molecules.
 Much
weaker than
chemical bonds
within molecules.
 a.k.a.
van der Waals forces
C. Johannesson
Intermolecular Forces
 Attraction
molecules
between
B. Types of IMF
C. Johannesson
B. Types of IMF
 London
Dispersion Forces
View animation online.
C. Johannesson
Dispersion
 Weak
forces caused from temporary
shifts in e- density
Polarity
(Differing Electronegativities)
Eletronegativity Difference
Bond Character
> 1.7
ionic
0.4 – 1.7
polar covalent
< 0.4
Nonpolar covalent
B. Types of IMF
 Dipole-Dipole
-
Forces
+
View animation online.
C. Johannesson
Dipole-Dipole
 Between
partial positive area of one
molecule with the partial negative
area of another
 Occurs in polar molecules
B. Types of IMF
 Hydrogen
Bonding
C. Johannesson
Hydrogen Bonding



Special dipole-dipole
Between H and a highly
electronegative atom (O, N, F)
SPECIAL NOTE – THE H atom has to be
directly chemically bonded to an O, N, or
F
Your DNA
C. Determining IMF
 CH2Cl2
• polar = dispersion, dipole-dipole
 CH4
• nonpolar = dispersion
 HF
• H-F bond = dispersion, dipoledipole, hydrogen bonding
C. Johannesson
II. Physical Properties
A. Liquids vs. Solids
IMF Strength
Fluid
Density
Compressible
Diffusion
LIQUIDS
SOLIDS
Stronger than
in gases
Very strong
Y
N
high
high
N
N
slower than in
gases
extremely slow
C. Johannesson
B. Liquid Properties
 Surface
Tension
• attractive force between particles in a
liquid that minimizes surface area
C. Johannesson
B. Liquid Properties
 Capillary
Action
• attractive force between the surface of
a liquid and the surface of a solid
water
C. Johannesson
mercury
C. Types of Solids
 Crystalline
- repeating geometric
pattern
• covalent network
• metallic
• ionic
• covalent molecular
 Amorphous
decreasing
m.p.
- no geometric pattern
C. Johannesson
C. Types of Solids
Ionic
Metallic
(NaCl)
C. Johannesson
C. Types of Solids
Covalent
Molecular
Covalent
Network
(H2O)
(SiO2 - quartz)
C. Johannesson
Amorphous
(SiO2 - glass)
III. Changes of State
A. Phase Changes
C. Johannesson
A. Phase Changes
 Evaporation
• molecules at the surface gain enough
energy to overcome IMF
 Volatility
• measure of evaporation rate
• depends on temp & IMF
C. Johannesson
A. Phase Changes
Boltzmann Distribution
p. 477
temp
# of Particles
volatility
IMF
volatility
Kinetic Energy
C. Johannesson
A. Phase Changes
 Equilibrium
• trapped molecules reach a balance
between evaporation & condensation
C. Johannesson
A. Phase Changes
p.478
Pressure
• pressure of vapor above
a liquid at equilibrium
• depends on temp & IMF
• directly related to volatility
temp
v.p.
v.p.
 Vapor
IMF
C. Johannesson
temp
v.p.
A. Phase Changes
 Boiling
Point
• temp at which v.p. of liquid
equals external pressure
• depends on Patm & IMF
• Normal B.P. - b.p. at 1 atm
Patm
b.p.
IMF
C. Johannesson
b.p.
A. Phase Changes
 Melting
Point
• equal to freezing point
IMF
m.p.
 Which
has a higher m.p.?
polar
• polar or nonpolar?
• covalent or ionic?
ionic
C. Johannesson
A. Phase Changes
 Sublimation
• solid  gas
• v.p. of solid equals
external pressure
 EX:
dry ice, mothballs,
solid air fresheners
C. Johannesson
B. Heating Curves
Gas - KE 
Boiling - PE 
Liquid - KE 
Melting - PE 
Solid - KE 
C. Johannesson
B. Heating Curves
 Temperature
Change
• change in KE (molecular motion)
• depends on heat capacity
 Heat
Capacity
• energy required to raise the temp of 1
gram of a substance by 1°C
• “Volcano” clip - water has a very high
heat capacity
C. Johannesson
B. Heating Curves
 Phase
Change
• change in PE (molecular arrangement)
• temp remains constant
 Heat
of Fusion (Hfus)
• energy required to melt 1 gram of a
substance at its m.p.
C. Johannesson
B. Heating Curves
 Heat
of Vaporization (Hvap)
• energy required to boil 1 gram of a
substance at its b.p.
• usually larger than Hfus…why?
 EX:
sweating,
steam burns,
the drinking bird
C. Johannesson
C. Phase Diagrams
 Show
the phases of a substance at
different temps and pressures.
C. Johannesson
Phase Diagrams
 Triple
point - The temperature and
pressure at which the solid, liquid, and
vapor phases of a pure substance can
coexist in equilibrium.
 *Be
able to know what phase change
occurs when pressure and/or temperature
changes when looking a phase diagram.
C. Johannesson