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Sparks
CH301
WHY IS EVERYTHING SO
DIFFERENT? Gas, Liquid or Solid?
UNIT 3 Day 6
What are we going to learn today?
MO of large molecules
Recognize different molecules have different
physical properties
Classify Intermolecular Forces
Most molecules have
A. An even number of electrons
B. An odd number of electrons
C. Equal chance of even or odd
POLL: CLICKER QUESTION
Most molecules are
A. diamagnetic
B. paramagnetic
C. Evenly split between the two
POLL: CLICKER QUESTION
How is this tool used..
Calculate the lowest
energy geometry;
Where is the electron
density
What if it is a complicated molecule with lots of atoms
It is hard to relate the MO to AO
None the less the MOs are useful
Other way we use MO, just the pi electrons
VB for sigma bonds
MO for the pi bond
Where are the electrons?
Delocalized around the molecule
Typical MO for organic molecule
Almost always diamagnetic
HOMO/LUMO
Energy gap
Light absorption
Dyes – homo lumo gap is
the color that is
absorbed, gaps as a
function of structure
MO picture of Ethanol
VSEPR and VB to get visual image
Predict Polar just from ball and stick
Chemical Composition & Shape
Physical Properties?
GAS? or LIQUID?
Types of Forces
Intramolecular Forces: forces that hold together an individual molecule
Types of Forces
Intermolecular Forces: forces between
different molecules
e.g., forces between:
separate CO2 molecules in CO2
separate H2O molecules in H2O
Thought Question!
H2O(g) + 927 kJ 2H(g) + O(g)
H2O(l) + 40.7 kJ H2O(g)
For water, which are stronger:
A.The intermolecular forces.
B.The intramolecular forces.
What dominates the interaction in
condensed phases?
What are these forces?
Classify forces.
Define IMF.
REMEMBER TAPE
REMEMBER CHARGED ROD and LIQUIDS
INTERMOLECULAR FORCES
DOMINATE FORCE IN CHEMISTRY – COULOMBIC
INTERMOLECULAR FORCES
DOMINATE FORCE IN CHEMISTRY – COULOMBIC
Qualify the word “intermolecular”
Boling Point: 1413 °C
INTERMOLECULAR FORCES
CONDENSED PHASE – BUT NOT IONIC
MOLECULAR CONDENSDED PHASE:
MOLECULAR LIQUID OR MOLECULAR SOLIDS
“PARTICLE IS A MOLECULE”
Intermolecular forces are
based on attraction of
opposite charges.
Electrostatic forces
In covalent molecules,
intermolecular forces are
based on the molecule
polarity.
REMEMBER:
A molecule which is polar overall will have a NET
DIPOLE.
From now on we refer to this type of molecule as a
DIPOLE.
INTERMOLECULAR FORCES: dipole-dipole
Attractive force between
partial negative end of
one molecule and
partial positive end of
another molecule.
Strength depends on
distance and dipole
moment.
E 1
r3
POLL: CLICKER QUESTION
CLICKER QUESTION
ALL NONPOLAR COMPOUNDS ARE GASES:
A) TRUE
B) FALSE
Important Information
LM23 posted
Extra, non-graded practice:
Laude LM Lecture 16 & 17