chm 112 m. prushan chapter 10 liquids, solids, and phase change
TRANSCRIPT
CHM 112 M. Prushan
Chapter 10Liquids, Solids, and Phase
Change
CHM 112 M. Prushan
Why Do Solids and Liquids Exist?
• Intermolecular Forces
gases – Little to no attraction between
molecules
CHM 112 M. Prushan
Why Do Solids and Liquids Exist?
• Intermolecular Forces
liquids – Fairly strong forces between a
few molecules
CHM 112 M. Prushan
Why Do Solids and Liquids Exist?
• Intermolecular Forces
solids – Strong forces prevent large amount of motion between molecules/atoms
CHM 112 M. Prushan
What makes a molecule polar?• Polar molecules are said to possess a
permanent dipole moment.
• Dipole moment measured in units of
Debye (Q x r ) [charge x distance]
1 D = 3.336 x 10-30 coulomb metersProf. Peter DebyeNoble Prize 1936
CHM 112 M. Prushan
Dr. Prushan, enough physics, what does it mean?
• OK… Let’s go back to Lewis Structures and VSEPR
• Examples:
Draw Lewis Structures and Predict the Geometry of : NH3, H2O, CH4, CH3Cl,CHCl3 CO2, CCl4
(Yes, there was a reason you needed this)
CHM 112 M. Prushan
Examples
NH
HH O
HH C OO
NH3 H2O CO2
Trigonal Pyramidal Bent Linear
Tetrahedral
CCl4
H
CH
HH
Cl
CCl
ClCl
CH3ClCH4
Cl
CH
HH
H
CCl
ClCl
CHCl3
CHM 112 M. Prushan
NH
HH O
HH C OO
Polar or Not Polar That is the Question?
NH3 H2O CO2
Trigonal Pyramidal Bent Linear
CHM 112 M. Prushan
NH
HH O
HH C OO
Polar or Not Polar That is the Question?
= 1.47 D = 1.85 D = 0 D
+
-
+
-
- - +
NH3 H2O CO2
Trigonal Pyramidal Bent Linear
CHM 112 M. Prushan
Polar or Not Polar That is the Question?
CCl4
H
CH
HH
Cl
CCl
ClCl
CH3ClCH4
Cl
CH
HH
H
CCl
ClCl
CHCl3
+
-
-
+
= 0 D = 0 D = 1.87 D = 1.90 D
CHM 112 M. Prushan
Types of Intermolecular Forces
• 4 main types of intermolecular forces
(1) London (Dispersion) Forces
(2) Dipole-Dipole Forces
(3) Ion-Dipole Forces
(4) Hydrogen Bonds
Increasing
Strength
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London (Dispersion) Forces
Weakest of the IM forces. All molecules have Dispersion forces
Result of interactions between instantaneous dipole moments.
Prof. Fritz London
CHM 112 M. Prushan
Dipole-Dipole Forces
• Result of permanent dipole moments in polar molecules
CHM 112 M. Prushan
Ion-Dipole Forces
The force which dissolves ionic compounds
A result of interactions between ions and solvent molecules
CHM 112 M. Prushan
Hydrogen Bonds
• Strongest of the intermolecular forces
• NOT a chemical bond
• MUST contain hydrogen covalently bonded to F, Cl, O or N.
• Essential for Life!
CHM 112 M. Prushan
If the boiling point of CO2 is , and CS2 is
Molecules with larger molecular weights have higher boiling points.
So why is H2O a liquid, but H2S is a gas?
Hydrogen Bonds
CHM 112 M. Prushan
BONDS… Hydrogen Bonds
CHM 112 M. Prushan
Why are Snow Flakes Hexagons?
CHM 112 M. Prushan
Hydrogen Bonds and Life
• Life Depends of H-bonds
• The “Stuff” of Life relies on them to stay together
Proteins, Enzymes Nucleic Acids (DNA, RNA)
Amino Acids Sugar-phosphate Backbond andBase Pairs
CHM 112 M. Prushan
Amino acids bond together to make polypeptides
The polypeptides fold to make the secondary structure of proteins
CH
C
N
HC
C
N
CH
N
CHN
HC
N
HCN
CH
N
HCN
O
O H
HO
HO
HO
HO
HO
HO
H
RRRR
R
R
R
How and Why does the alpha structure form??
Linus Pauling Discovered How, in 1948
While in bed with a cold…. Lets let him describe how…
CHM 112 M. Prushan
Now let’s try that…
Come on down and get a polypeptide
CHM 112 M. Prushan
CHM 112 M. Prushan
Hydrogen Bonds are also important in DNA
CHM 112 M. Prushan
N
NNH
N
NH2
NH
NNH
N
O
NH2
N
NH
NH2
O
NH
NH
O
O
Adenine
Guanine
Cytosine
Thymine
Which goes with which ???
A – T
G – C
Right??? BUT WHY????
Come on down and get some base pairs
CHM 112 M. Prushan
The Guanine-Cytosine (GC) Base Pair
CHM 112 M. Prushan
The Guanine-Cytosine (GC) Base Pair
CHM 112 Summer 2007 M. Prushan
Effect of Intermolecular forces on melting and
boiling points of molecular covalent substances
Increase only due to increase in MW,Since all are non-polar
1632
77132
Molecular wts.20
37
81
128
Why does HF have the highest BP?
Molecular wts.
BONDS… Hydrogen Bonds