1. INTERMOLECULAR FORCES
- Sutherland High School-
Robyn Harrison
Doc Scientia
Grade 11
2018

2. Interatomic forces Ionic Bonding Metallic Bonding Covalent Bonding01
Positive ion cores are bound together by a sea of delocalized electrons. :
For atoms to forms a compound, one of the following types of bonds must be formed 02
Ionic Bonding
Atoms transfer electrons and form positively and negatively charged ions. These oppositely charged ions attract each other with electrostatic forces. 03
Covalent Bonding
Electrons of different atoms are shared, and a molecule is formed.
TB. pg. 51 & 58

3. TB. pg. 52 Forces between molecules are called intermolecular forces.
In a liquid or solid state, there must be forces between the particles that will hold the particles together. If there were no such forces, the molecules would move apart and become a gas.
Ionic and metallic bonds are strong.
The intermolecular forces between small covalent molecules is what we will be focusing on.
TB. pg. 52
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4. TB. pg. 56 Let’s clarify first: POLAR MOLECULES
This is where one side of the molecule has a slightly positive charge and the other side has a slightly negative charge.
HOW DOES THIS HAPPEN?
When one atom is more electronegative than the other. So it tends to pull a shared pair of electrons more than the other.
TB. pg. 56
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5. Types of Intermolecular forces
TB. pg. 52
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6. 1. Ion-dipole forces TB. pg. 53
Occurs when a dipole approaches a positive or negative ion.
The dipole will move so that the side closest to the ion has the opposite charge.
When salt is dissolved in water – ions become “hydrated.” ???
𝑁 𝑎 + 𝑎𝑞 means the 𝑁 𝑎 + ion is hydrated.
TB. pg. 53
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7. Ion-induced dipole forces2.
Ion-induced dipole forces
This is when an ion affects the electron cloud around an atom or molecule when it is nearby, causing a temporary dipole.
Atom with no dipole.
Ion responds and the atom develops a dipole.
TB. pg. 54
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8. 3. Dipole- dipole forces TB. pg. 55
These are attraction forces between the slightly positive pole of one atom in the polar molecule and the slightly negative pole of the other atom in a polar molecule.
TB. pg. 55
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9. Dipole-induced forces4.
Dipole-induced forces
A polar molecule (permanent dipole) can induce a temporary dipole in a non-polar molecule or atom.
This results in an attractive force
between the two oppositely charged
dipoles. Very weak force.
TB. pg. 56
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10. Induced-dipole forces5.
Induced-dipole forces
(Dispersed or London forces)
When two non-polar molecules or atoms approach each other, there is a slight change in the charge distribution in the electron cloud of both molecules or atoms.
The electrons will not be exactly equally
arranged around the atom/molecule.
These are temporary and will disappear
and reform between other particles in
different directions.
TB. pg. 56
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11. 6.
Hydrogen Bonds
These occur between molecules in which hydrogen is bonded to a small atom with an extremely high electronegativity, as in compounds with oxygen, nitrogen and fluorine.
This bond is an electrostatic force between a
slightly negative charge on the electronegative
atom of one of the molecules and the slightly
positive charge on the hydrogen of one of the
other molecules.
TB. pg. 57
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12. Watch me
carefully!!!
TB. pg. 57

13. LIQUID MERCURY!!!!

14. SODIUM!!!!

15. MAGNESIUM!

16. Homework
Exercise 5
TB. pg

17. Intermolecular forces influence:
State
Size
Density
Boling and Melting points
Viscosity
Thermal Expansion
Thermal Conductors
TB. pg. 61
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18. 1. State of molecules Solids –strong intermolecular forces.
Liquids – weaker
Gases - weakest
TB. pg. 61
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19. 2.
Size of molecules
Larger molecules – greater tendency towards polarity. More electrons and greater distance over which it can move.
Greater molecular mass – greater intermolecular force.
E.g. Petrol 𝐶 8 𝐻 18 (liquid) has weaker intermolecular forces than wax 𝐶 23 𝐻 48 (solid). Why?
TB. pg. 61
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20. 3.
Density of molecules
Density is the number of particles per unit volume.
Higher density – stronger intermolecular forces.
Low density
Low IMF
High density
High IMF
TB. pg. 62
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21. Waters density decreases when it freezes…
EXCEPT WATER!!!!
Waters density decreases when it freezes…
TB. pg. 62

22. Boiling and Melting Point4.
Boiling and Melting Point
Stronger forces – more energy is needed to overcome forces – higher melting and boiling points.
Why so high???
TB. pg. 62
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23. 5. Viscosity This is an indication of a liquid’s resistance to flow.
Higher the intermolecular forces – higher viscosity.
Increase temperature – decrease viscosity
as intermolecular forces decrease.
TB. pg. 63
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24. 6. Thermal expansion This means that the material expands on heating.
More energy – IMF weaken – particles move further apart – volume increases. (expands).
TB. pg. 66
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25. 7.
Thermal conductors
Covalent structures and molecules (non-metals) are bad conductors as there are no free electrons.
Exceptions: diamond, graphite.
Metallic bonds (metals) are good thermal conductors as the delocalized electrons are free to move.
TB. pg. 66
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26. READ THE EXPERIMENTS….
This is your practical
for Term 2.
eh..

27. Homework
Exercise 6
TB. pg

28. Chemistry of Water Microscopic Structure of Water O H H Polar Molecule
Angular / Bent shape
Polar Molecule
𝛿 − O
Greenhouse Gas
The polar characteristic of water allows it to absorb infrared radiation from the sun. This way, the ocean acts as a heat reservoir and keeps the earth’s climate moderate.
Strong intermolecular forces (WHY) H H
𝛿 +
𝛿 +
TB. pg
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29. Specific Heat Capacity1.
Properties of Water
Specific Heat Capacity
This is the amount of energy necessary to change the temperature of 1kg of a substance by 1ºC.
When a substance changes state, energy is absorbed or released. However, the temperature does not change. This is called “latent heat or latent energy.”
Water has a high specific heat capacity (why) and also a high latent energy.
Waters specific heat capacity is responsible for:
Moderate climate change.
Regulates body temperature.
Temperature.
TB. pg. 77
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30. Melting and Boiling Point2.
Melting and Boiling Point
Melting point: 0ºC and Boiling Point: 100ºC.
These temperatures are higher than expected. Because of the strong hydrogen bonds – a lot of energy is needed to overcome the IMF.
They must be this high – otherwise most of our water would be in a gaseous state.
TB. pg. 78
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31. Density of water and ice3.
Density of water and ice
As liquid water cools, its density increases until it reaches a maximum at about 4ºC. As it continues to cool, the water expands and the density decreases.
The reason for this is that the molecules form strong hydrogen bonds with three other water molecules to
form the open hexagonal structure.
Ice layers on top of frozen lakes – insulating
layer – organisms can still live in the water below.
TB. pg. 78
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32. 4. Adhesion and Cohesion TB. pg. 78
Cohesive forces – Forces between the same type of molecules. (Water and water)
Adhesive force – Forces between two
different types of molecules.
(water and glass)
TB. pg. 78
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33. 5.
Surface Tension
This is due to the cohesive forces of molecules on the surface of a volume of water.
Every water molecule is attracted to every other water molecule.
Top layer has air molecules above them.
Adhesive force between water and air is weaker than the cohesive forces between water.
Net force causes a tension force on the top layer.
Allows very light objects to rest on the surface,
TB. pg. 79
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34. 6.
Capillary Action
The tendency of a liquid to rise in a tube as a result of surface tension and is a result of adhesive properties of water molecules.
Straw – water molecules are attracted to the molecules of the straw.
TB. pg. 79
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35. A single drop of sea water under a microscope

36. Homework
Exercise 7
TB. pg