Chem 101
Chapter 6
"How full of creative genius is the air in
which these are generated!
I should hardly admire them more if real
stars fell
and lodged on my coat."
--Henry David Thoreau, 1856
Chapter 5
• No attractive/repulsive forces in
a gas
Question…
• How do snowflakes form?
Two types of ‘bonding’
• Chemical
–
– Results in very
strong connection
between atoms
• Secondary forces
–
–
–
–
Solids and Liquids
• NaCl
–
• Water
–
• Gasoline
–
Properties
• Compressibility
–
–
–
• Volume change as state changes
– 1 mole water…
What does that tell you about
attractive forces between
molecules in:
•
•
•
Phase Transitions
• Solid to liquid
•
• Liquid to solid
•
• Gas to solid
•
Temperature oC
Heating Curve
Energy added
Dipole-Dipole
• Occur between polar molecules
•
Ion-Dipole
• Occur between ions and molecules with
a dipole
•
• Did salt dissolve in ethanol in the lab?
Hydrogen Bonding
•
• Results from large difference in
electronegativity
•
London Dispersion
• Hexane – is it polar?
•
•
• Induced dipoles
•
H2 Bond
• ONLY BETWEEN MOLECULES
WITH H-F, H-O, and H-N
London Dispersion
• NONPOLAR MOLECULES ONLY
BOND TO EACH OTHER THIS
WAY
Predict Polarity…
• O2
•
• CH2F2
•
Polarity and boiling
• See table 6.1 on page 152
Fractional Distillation
Review
• Which of the following can form
hydrogen bonds?
–
–
–
–
–
Review
• Non Polar Molecules
–
• Polar Molecules
–
• H-bonding molecules
–
Strength of Bonds
• LD<Dipole-Dipole<H-bond
• Surface Tension
–
Soap
• Salt of a fatty acid
– See page 158
• Two ends
–
–
– What type of bonding?
Solutions
• Why do some mixtures form solutions
and others don’t?
–
–
–
• Key is in the type of forces involved
•
Practice
• Are the following miscible?
–
–
Vaporization
• Defined
–
–
–Just happens
•
–Vapor – if the liquid and gas are
both present
Dynamic Equilibrium
• Occurrence of two processes at the
same time
–
• Closed system
How do Secondary forces
affect vapor pressure?
• High attraction –
• Low attraction –
• How does this affect boiling
point?
Problem
• CH3OH and CH3I are both polar
and the latter is much more
massive. Why is methyl
iodide’s vapor pressure at 22oC
almost 4 times greater than
methyl alcohol?
Problem 2
• Which has a higher boiling point and
why?
–
Review
• All gas laws, when and how to use them
• Pressure conversions
• Secondary forces
– How they impact properties of substances
– Their strength
– Polarity
– Vaporization
– Why you sweat when you exercise
– Heating curve