INTERMOLECULAR FORCES
-
- FORCES
- INTRAMOLECULAR
BONDING WITHIN A MOLECULE
- INTERMOLECULAR
BETWEEN ONE MOLECULE AND ANOTHER
BULK PROPERTIES, MELTING POINT, BOILING POINT, ETC.
MUST EXIST OR EVERYTHING WOULD BE A GAS
SOME MUST BE STRONGER THAN OTHERS
INTERMOLECULAR ARE WEAKER THAN INTRAMOLECULAR
41 kJ TO VAPORIZE 1 MOLE OF WATER
465 kJ TO BREAK 1 MOLE OF O-H BONDS IN WATER
TWO CONFLICTING FORCES
INTERMOLECULAR FORCES
PULLING MOLECULES TOGETHER
CAN OFTEN USE BOILING POINT OR MELTING POINT AS A QUALITATIVE "MEASURE"
-
- DEFINITIONS:
- STATES OF MATTER (COMMON PHASES)
- PHASE CHANGES
- VAPOR PRESSURE
THE PARTIAL PRESSURE OF THE GAS PHASE WHICH IS IN DYNAMIC EQUILIBRIUM WITH
THE CONDENSED PHASE AT A GIVEN TEMPERATURE.
- PHASE CHANGE TEMPERATURES
MELTING POINT
THE TEMPERATURE AT WHICH THE SOLID PHASE IS IN
EQUILIBRIUM WITH THE LIQUID PHASE
BOILING POINT
THE TEMPERATURE AT WHICH THE VAPOR PRESSURE OF A LIQUID IS EQUAL
TO THE APPLIED PRESSURE
- ENERGY OF PHASE CHANGES
MOLAR HEAT OF VAPORIZATION
HEAT NEEDED TO VAPORIZE ONE MOLE OF A SUBSTANCE AT ITS NORMAL BOILING POINT
MOLAR HEAT OF FUSION
HEAT NEEDED TO MELT ONE MOLE OF A SUBSTANCE AT ITS NORMAL MELTING POINT
MOLAR HEAT OF SUBLIMATION
HEAT NEEDED TO VAPORIZE (SUBLIME) ONE MOLE OF SOLID
- SPECIFIC HEAT
ENERGY REQUIRED TO RAISE THE TEMPERATURE OF ONE GRAM OF THE SUBSTANCE
BY ONE DEGREE CELSIUS
DIFFERENT FOR SOLID, LIQUID, AND GAS
-
SPECIFIC HEATS OF H2O
| PHASE |
SPECIFIC HEAT (J/go) |
| ICE (SOLID) |
2.09 |
| WATER (LIQUID) |
4.18 |
| STEAM (GAS) |
2.02 |
|---|
-
HEATING AND COOLING CURVES
-
- INTERMOLECULAR FORCE TYPES
- ION - DIPOLE (SALT AND WATER)
- MAGNITUDE DEPENDS ON:
SIZE
SMALLER - GETS CLOSER TOGETHER!
- IF WATER IS INVOLVED CALLED "HYDRATION"
-
- DIPOLE - DIPOLE
- MAGNITUDE DEPENDS ON:
-
BOILING POINTS OF POLAR MOLECULES
| MOLECULE |
BOILING POINT |
DIPOLE MOMENT |
| BUTANE |
-0.5 |
0 |
| METHYL ETHYL ETHER |
10 |
1.23 |
| ACETONE |
56 |
2.88 |
| ---------- |
---------- |
---------- |
| HCl |
-83 |
1.1 |
| HBr |
-67 |
0.82 |
| HI |
-40 |
0.38 |
-
- PAY ATTENTION TO POLARIZIBILITY!!
-
- INDUCED DIPOLE - ION OR DIPOLE
- MAGNITUDE DEPENDS ON:
POLARIZIBILITY OF NONPOLAR
FUNCTION OF NUMBER OF ELECTRONS
-
- INDUCED DIPOLES - INDUCED DIPOLES
- (LONDON FORCES OR DISPERSION FORCES)
- MAGNITUDE DEPENDS ON:
- ORIGIN OF DISPERSION FORCES
-
BOILING POINTS OF NOBLE GASES
| ATOM |
BOILING POINT |
| He |
-269 |
| Ne |
-246 |
| Ar |
-186 |
| Kr |
-153 |
-
BOILING POINTS OF NONPOLAR DIATOMIC MOLECULES
| MOLECULE |
BOILING POINT |
| H2 |
-253 |
| F2 |
-188 |
| Cl2 |
-35 |
| Br2 |
+59 |
| I2 |
+184 |
-
BOILING POINTS OF TETRAHEDRAL NONPOLAR MOLECULES
| MOLECULE |
BOILING POINT |
| CH4 |
-162 |
| CF4 |
-128 |
| CCl4 |
+77 |
| CBr4 |
+189 |
-
- PAY ATTENTION TO POLARIZIBILITY!!
-
BOILING POINTS
| MOLECULE |
DIPOLE MOMENT |
BOILING POINT |
| CH3Cl |
1.87 D |
-24 |
| CH2Cl2 |
1.60 D |
+40 |
| CHCl3 |
1.01 D |
+62 |
| CCl4 |
0 D |
+77 |
-
- CCl4 IS VERY POLARIZIBLE
- DISPERSION FORCES ARE ALSO A FUNCTION OF SHAPE
-
-
- VAN DER WAAL'S FORCES ARE WEAK FORCES
- DIPOLE-DIPOLE
- DIPOLE-INDUCED DIPOLE
- DISPERSION FORCES
-
- HYDROGEN BONDING
- A MUCH STRONGER INTERMOLECULAR FORCE
- A VERY IMPORTANT INTERMOLECULAR FORCE
- INVOLVES
HYDROGEN ON A SMALL, ELECTRONEGATIVE ELEMENT
ANOTHER SMALL, ELECTRONEGATIVE ATOM
-
BOILING POINTS OF COVALENT HYDRIDES
| MOLECULE |
BOILING POINT |
MOLECULE |
BOILING POINT |
MOLECULE |
BOILING POINT |
| CH4 |
-162 |
HF |
? |
H2O |
? |
| SiH4 |
-112 |
HCl |
-83 |
H2S |
-61 |
| GeH4 |
-90 |
HBr |
-67 |
H2Se |
-42 |
| SnH4 |
-70 |
HI |
-40 |
H2Te |
-4 |
-
- HYDROGEN BONDING DATA
-
- HYDROGEN BONDING IS MORE THAN DIPOLE DIPOLE
- IT'S DIRECTIONAL
- HF HAS THE STRONGEST HYDROGEN-BOND
WHY DOES WATER HAVE A HIGHER BOILING POINT?
FOUR HYDROGEN BONDS PER WATER!
-
- DIRECTIONAL NATURE OF HYDROGEN BOND!
- WATER HAS EXTENSIVE HYDROGEN BONDING
HOLES IN ICE CAUSE ICE TO FLOAT IN WATER
WHEN ICE MELTS, PART OF THIS 3-D STRUCTURE IS
MAINTAINED AND THE DENSITY INCREASES
AT 4o THE HOLES HAVE COLLAPSED AND WATER HAS ITS MAXIMUM DENSITY
AS WATER IS WARMED ABOVE 4o, THE INCREASE IN KINETIC ENERGY FORCES
MOLECULES A LITTLE FURTHER APART AND THE DENSITY DECREASES (LIKE EVERYTHING ELSE)
-
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