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Ch.11 notes – P.1
Ch.11 – Intermolecular Forces
A. Introduction
 For molecular substances, the ___________________________ (covalent bonding)
between atoms are strong, but the ______________________________ between
molecules are weak.
 There are two types of intermolecular forces:
1. _________________________________________
2. _________________________________________
B. Van der Waals’ forces
It consists of three types of intermolecular attractions:
1. Dipole-dipole interactions
Polar molecules have _______________________________________. They tend to
orientate themselves in such a way the attractive forces are maximized.
Fig. 11-4
2. Dipole-induced dipole interactions
When a non-polar molecule approaches a polar molecule, a dipole will be
___________ in the non-polar molecule.
Fig. 11-5
3. Instantaneous dipole-induced dipole interactions
 It seems that there do not exist any forces between non-polar molecules. However,
non-polar molecules, even noble gases can be solidified at low temperature and
under high pressure.

For non-polar molecules / atoms, the electron cloud distribution is generally
____________________.
 At any particular moment, it is likely to be ______________________________
___________. Thus, it possesses an _____________________________________.
 The instantaneous dipole moment will ____________________________ in the
neighbouring atom, hence an attractive force is resulted.
Ch.11 notes – P.2
 These forces between fluctuating dipoles are often called ___________________
or _____________________.
Fig 11-6
 The greater the _________________________________ in a molecule, the
instantaneous dipole can be set up more easily, and the van der Waals’ forces is
_________________.
Table 11-2
 The van der Waals’ forces also increase with _____________________ of the
molecule.
e.g.
4. Magnitude of van der Waals’ forces:
Table 11-1
C. Van der Waals’ radii
1. The ___________________ is one half of the distance between two atoms in the
__________ molecule.
2. The _______________________ is one half of the distance between the nuclei of
two atoms in _________________ molecules.
Fig 11.9
Fig. 11-8
3. Since van der waals’ forces is much weaker than a covalent bond, the van der waals’
radius of a molecule is much _____________ than its covalent radius.
Fig. 11-10
Ch.11 notes – P.3
D. Hydrogen bonding
1. Hydrogen bonding is a particularly _________________________________
interaction.
 When hydrogen is bonded to a __________________________ atom, the bonding
electron pair is drawn towards the electronegative atom.
 As hydrogen has no inner shell electron and is very small in size, a
_____________________________________________ is developed.
 The attraction between the ___________________electrons of the electronegative
atom and the positively charged _______________________ of another molecule
is called a hydrogen bond.
Fig. 11-15
 The strength of a hydrogen bond is about __________________ of a covalent
bond.
Table 11-3
 The essential requirements for the formation of a hydrogen bond:
a) A hydrogen atom usuallly bonded to a highly electronegative atom ___________________.
b) An ________________________ electrons on the electronegative atom.
2. Hydrogen bonds in different cases:
a) between same kind of molecules.
b) between different kinds of molecules.
c) within one molecules.
Ch.11 notes – P.4
3. Experimental determination of the strength of the hydrogen bond:
a) Hydrogen bonding is formed between trichloromethane and ethyl ethanoate.
b) When these two liquids are mixed, a _____________________________ is
observed.
c) From the specific heat capacities and the quantities of reagents used, the
enthalpy change that forms hydrogen bonds can be calculated.
4. Importance of hydrogen bonding in physical phenomena
a) Anomalous properties of the second period hydrides
Fig. 11-17
The abnormally ________________________________________________ of
NH3, H2O and HF can be explained by the present of hydrogen bonds.
b) Boiling points and solubilities of alcohol
Fig. 11-18
 The boiling points of alcohols are much __________ than the corresponding
thiols. These can be explained by the present of hydrogen bonds between
alcohol molecules.
 These can also explain why the lower alcohols can be _________________with
water.
c) Dimerization of carboxylic acids
When the molar mass of carboxylic acid are found from measurements in the
vapour phase, the values are up to ____________ the values calculated from the
chemical formulae. This is because the molecules form ____________ through
the formation of hydrogen bonds:
Ch.11 notes – P.5
d) The different in boiling points between isomers
Trans-butenedioic acid forms extensive ____________________ hydrogen
bonds with neighbouring molecules; while cis-butenedioic acid forms
_____________________ hydrogen bonding and forms less extensive
intermolecular hydrogen bonds with neighbouring molecules.
e) Different in hardness between anhydrous and hydrated salt
Anhydrous magnesium sulphate solid is much ___________ than its hydrated
form (MgSO4.7H2O), this is because in anhydrous form, the cations and anions
are linked by _________________________; while in the hydrated form, water
molecules are present between the ions and linked by hydrogen bonds only,
hence the structure is much weaker.
5. Importance of hydrogen bonds in biochemistry
a) Hydrogen bonding in water and ice
 In water, the molecules are in ___________________________, and the
hydrogen bonds are formed and broken continually.
 In ice, molecules are ________________ in such a way that the maximum
number of hydrogen bonds is formed. This results in a three-dimensional
__________________________ structure which is an _________ structure.
Fig. 11-21
 This accounts for the fact that ice is _____________________ than water at 0oC.
This fact makes ponds and lakes freeze from the surface downwards, and the
layer of ice ___________________ the water below and prevents complete
solidification, this allows aquatic lives to survive.
Ch.11 notes – P.6
b) Hydrogen bonding in proteins
 The primary structure of a protein consists of a sequence of amino acids:
 Protein chains are held in _______________________ to one another by
hydrogen bonds. This creates the _____________________ structure of protein.
 In many proteins, including those in hair, wool and nails, hydrogen bonding
causes the protein chain to become _____________ into a tightly coiled
___________.
Fig. 11-23
c) Hydrogen bonding in DNA
 DNA is present in the nuclei of living cells and carries ______________
___________________.
 DNA consists of two macromolecular strands spiralling round each other in the
form of a ____________________.
Fig. 11-23, 11-24
 The two nucleic acid chains are held together by _____________________.
 When a cell divides, the double helix of the DNA molecule ____________ by
breaking down the hydrogen bonds.
 A ________________________ chain is formed adjacent to each of the original
chain by the formation of new hydrogen bonds. Each of the newly formed
double helix is received by each of the two cells. This gives an explanation of
the ________________ of the DNA in every cell of an organism.
Ch.11 notes – P.7
E. Phase diagrams of carbon dioxide and water
A phase diagram is a graph showing the relationship between solid, liquid and vapour
phase over a range of ________________ and ________________.

A typical phase diagram:
About the phase diagram:
1. Three curves appear, bounding the graph into 3 regions, each region represents the
particular_______________ phase that is stable and can exist under those conditions.
2. Each point on the 3 curves represents the conditions under which ________________
phases of the substance ________________at _____________________.
a) Line AT: __________________curve. Along the line, solid phase and liquid
phase coexist at equilibrium.
b) Line CT: ____________________curve. Along the line, liquid phase and vapour
phase coexist at equilibrium.
c) Line BT: __________________curve. Along the line, solid phase and vapour
phase coexist at equilibrium.
Ch.11 notes – P.8
3. Point T: _________________. This point represents the temperature and pressure at
which the solid, liquid and vapour phases are in equilibrium.
4. Point C: _______________. At temperature higher than the critical temperature, the
liquid phases become __________________________ from the vapour phase, and
increasing the pressure cannot liquefy gas.
Questions:
On the phase diagram, state what happens,
a) At constant temperature, the pressure is increased at point I?
b) At constant temperature, the pressure is decreased at point II?
c) At constant pressure, the temperature is increased at point II?
d) At constant pressure, the temperature is decreased at point III?
e) At point III, if the pressure is increased slightly, how could we maintain the
equilibrium state of the system?
f) At point T, if the temperature is increased slightly, is it possible to maintain the three
phases equilibrium state?
Ch.11 notes – P.9

Phase diagram of carbon dioxide:
a) under 1 atm, and 25℃, carbon dioxide is in the _________________phase.
b) Under 1 atm, when carbon dioxide is heated from -80℃ to 25℃, it changes from
___________phase to __________________phase, i.e. it ____________________.
c) It is _____________________for carbon dioxide to exist as liquid at 1atm, however
we could liquefy carbon dioxide at ____________________________.
Ch.11 notes – P.10

Phase diagram of water:
a) Under 1 atm, and 25℃, water is in the _______________________phase.
b) Different from a typical phase diagram, the solid-liquid equilibrium line slant to the
____________________, i.e. at constant temperature, ____________________ pressure
favors the melting of ice.
This is the consequence of the pressure of __________________________in ice, which
results in an __________________. An increase in pressure will cause the collapse of the
structure and produce the water which is denser than ice.
c) The dotted curve TD represents _______________ of water.