1. Chemical Bonding and Interactions
The Ties That Bind
Chemical Bonding and Interactions

2. Chemical Bonding and Interactions
Stable Electron Configurations
Electron-Dot (Lewis) Structures
Drawing, Rules for Drawing
The Octet Rule
Some Exceptions to the Rule
Ionic Bonding
Naming ionic compounds
Drawing
Covalent Bonding
Naming covalent compounds
Electronegativity and Polar Covalent Compounds
Molecular Shapes and the VSEPR Theory
Intermolecular Forces of Attraction
H-bonds, Dipole-Dipole, Ion-Dipole, London Dispersion Forces

3. INTERMOLECULAR FORCES OF ATTRACTION

4. A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary.
2 Phases
Solid phase - ice
Liquid phase - water
11.1

5. Intermolecular Forces
Intermolecular forces are attractive forces between molecules.
Intramolecular forces hold atoms together in a molecule.
Intermolecular vs Intramolecular
41 kJ to vaporize 1 mole of water (inter)
930 kJ to break all O-H bonds in 1 mole of water (intra)
“Measure” of intermolecular force
boiling point
melting point
DHvap
DHfus
DHsub
Generally, intermolecular forces are much weaker than intramolecular forces.
11.2

6. Intermolecular Forces

7. Intermolecular Forces
Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
Ion-Dipole Interaction
11.2

8. Intermolecular Forces

9. 11.2

10. Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
11.2

11. Intermolecular Forces
Dipole-Dipole Forces
There is a mix of attractive and repulsive dipole-dipole forces as the molecules tumble.
If two molecules have about the same mass and size, then dipole-dipole forces increase with increasing polarity.

12. Intermolecular Forces
London Dispersion Forces
Weakest of all intermolecular forces.
It is possible for two adjacent neutral molecules to affect each other.
The nucleus of one molecule (or atom) attracts the electrons of the adjacent molecule (or atom).
For an instant, the electron clouds become distorted.
In that instant a dipole is formed (called an instantaneous dipole).

13. Intermolecular Forces
London Dispersion Forces

14. Intermolecular Forces
London Dispersion Forces
One instantaneous dipole can induce another instantaneous dipole in an adjacent molecule (or atom).
Instantaneous dipoles are called London Dispersion Forces.
Polarizability is the ease with which an electron cloud can be deformed.
The larger the molecule (the greater the number of electrons) the more polarizable.

15. Intermolecular Forces
London Dispersion Forces

16. Intermolecular Forces
London Dispersion Forces
London dispersion forces increase as molecular weight increases.
London dispersion forces exist between all molecules.
London dispersion forces depend on the shape of the molecule.
The greater the surface area available for contact, the greater the dispersion forces.
London dispersion forces between spherical molecules are lower than between sausage-like molecules.

17. Intermolecular Forces
Hydrogen Bond
The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A H … B or
A & B are N, O, or F
11.2

18. Hydrogen Bond
11.2

19. Why is the hydrogen bond considered a “special” dipole-dipole interaction?
Decreasing molar mass
Decreasing boiling point
11.2

20. Intermolecular Forces
Hydrogen Bonding
Hydrogen bonds are responsible for:
Ice Floating
Solids are usually more closely packed than liquids;
therefore, solids are more dense than liquids.
Ice is ordered with an open structure to optimize H-bonding.
Therefore, ice is less dense than water.
In water the H-O bond length is 1.0 Å.
The O…H hydrogen bond length is 1.8 Å.
Ice has waters arranged in an open, regular hexagon.
Each + H points towards a lone pair on O.
Ice floats, so it forms an insulating layer on top of lakes, rivers, etc. Therefore, aquatic life can survive in winter.

21. Ice is less dense than water
Water is a Unique Substance
Maximum Density
40C
Density of Water
Ice is less dense than water
11.3

23. Intermolecular Forces
Hydrogen Bonding
Hydrogen bonds are responsible for:
Protein Structure
Protein folding is a consequence of H-bonding.
DNA Transport of Genetic Information

24. Intermolecular Forces
Comparing Intermolecular Forces

25. Strong intermolecular forces
Properties of Liquids
Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area.
Strong intermolecular forces
High surface tension
11.3

26. Some Properties of Liquids
Surface Tension

27. Properties of Liquids
Cohesion is the intermolecular attraction between like molecules
Adhesion is an attraction between unlike molecules
Adhesion
Cohesion
11.3

28. Strong intermolecular forces
Properties of Liquids
Viscosity is a measure of a fluid’s resistance to flow.
Strong intermolecular forces
High viscosity
11.3

29. Ultrahydrophobic surfaces

31. PHASE CHANGES
We can use the concepts of intermolecular forces of attraction to explain the physical phase changes

32. Phase Changes Energy Changes Accompanying Phase Changes
Surface molecules are only attracted inwards towards the bulk molecules.
Sublimation: solid  gas.
Vaporization: liquid  gas.
Melting or fusion: solid  liquid.
Deposition: gas  solid.
Condensation: gas  liquid.
Freezing: liquid  solid.
Energy Changes Accompanying Phase Changes
Energy change of the system for the above processes are:

33. Phase Changes Energy Changes Accompanying Phase Changes
All phase changes are possible under the right conditions (e.g. water sublimes when snow disappears without forming puddles).
The sequence
heat solid  melt  heat liquid  boil  heat gas
is endothermic.
cool gas  condense  cool liquid  freeze  cool solid
is exothermic.

34. Phase Changes
Energy Changes Accompanying Phase Changes

35. Phase Changes
Heating Curves

36. Test yourself
Which has a higher boiling point, ethane (C2H6) or dodecane (C12H26)?
What kind of IFA will be present in the following combinations/mixtures?
Water and ammonia
Octane and water
CCl4 and CHCl3
Hydrofluoric acid (HF) and water?
Acetic acid and cysteine? (see board for structures)
Water and NaCl
Which has a higher boiling point, neopentane or n-pentane? (See board for structures)
Which will have a higher boiling point:
Ne or Xe
N2 or Kr