INTERMOLECULAR FORCES
(IMF)
INTERMOLECULAR FORCES ARE BETWEEN MOLECULES
WHEREAS
INTRAMOLECULAR FORCES ARE WITHIN THE
MOLECULE
INTERMOLECULAR FORCES ARE:
1.)Van der Waal forces (also called London
dispersion forces)
2.)dipole-dipole forces
3.)hydrogen bonding
INTRAMOLECULAR FORCES ARE:(ionic, covalent &
metallic)
Van der Waal forces
(London Dispersion Forces)
• Are the weakest IMF
• Exists between nonpolar molecules and noble
gases
• Occur when temporary dipoles(positive endnegative end) form within a molecule
• Since electrons are in constant motion, there are
times when the electrons are more concentrated
in one location more than another. This causes
that area to be more negative than the other side
creating the temporary or instantaneous dipole
Van der Waal forces
(London Dispersion Forces)
Properties
• Low melting & boiling points
• The Van der Waal forces increase with
increasing size of the molecule so that makes
the melting & boiling point also increase with
increasing size
• Example: CH4 < C2H6 < C3H8 < C4H10
or F2<Cl2<Br2<I2
DIPOLE-DIPOLE
FORCES
• Are stronger than Van der Waal forces but
weaker than hydrogen bonding
• Exist between polar molecules( polar
molecules have permanent dipoles)
• The negative side of one molecule is attracted
to the positive side of another molecule
DIPOLE-DIPOLE FORCES
PROPERTIES
• Have higher melting & boiling points than
that of nonpolar molecules of the same size(
approx. same molar mass)
• The strength of the dipole-dipole forces
decreases as the degree of polarity decreases
• Example: HCl > HBr>HI b/c the
electronegativity values decreases from Cl to I
so H-Cl bond is more polar than H-I
HYDROGEN BONDING
• It is a type of dipole-dipole force but exist only
between hydrogen covalently bonded to
either nitrogen, oxygen or fluorine
• It is the strongest of the IMFs
HYDROGEN BONDING
PROPERTIES
• These molecules have the highest melting and boiling
points of all other covalent compounds
• If it wasn’t for the fact that it is hydrogen bonded,
water would be a gas not a liquid at room temperature.
• This is also why water is less dense as a solid than a
liquid. The water molecule is capable of bonding in 4
locations to another water molecule. As the molecules
get closer, a tetrahedral arrangement holds the
molecules a fixed distance away creating a fairly open
structure.
HYDROGEN BONDING
• Hydrogen bonding plays a role is so many
molecules and the properties they have.
Proteins and DNA just to name a few, are held
together by hydrogen bonds
Explain why the Higher Molar Mass
Compound, CF4, has a Lower Boiling Point
than H2Se
CF4
• Boiling Point; -150.0°C
• Molar Mass ~ 88 g/mole
Intermolecular Force; Dispersion
Force
H2Se
• Boiling Point; -42.0 °C
• Molar Mass ~ 81 g/mole
Intermolecular Force; DipoleDipole Force
SOLUBILITY
• Most polar molecules(except for large
molecules) are soluble in water due to the
attraction between their dipoles and those of
water
• Nonpolar molecules are not soluble in water
• However nonpolar molecules are soluble in
other nonpolar solvents
“LIKES DISSOLVE LIKE”
INTRAMOLECULAR vs
INTERMOLECULAR FORCES
• Intramolecular forces are much stronger than
intermolecular forces.
• Ionic and metallic bonds are much stronger than
covalent bonds
• INTERMOLECULAR FORCES
Van der Waal<Dipole-dipole< hydrogen bonding
SOLUBILITY
IONIC
COMPOUNDS
POLAR COVALENT
COMPOUNDS
NON-POLAR
COMPOUNDS
SOLUBITITY IN
POLAR SOLVENTS
SOLUBLE
SOLUBILITY
INCREASES AS
POLARITY
INCREASES
NON-SOLUBLE
SOLUBILITY IN
NON-POLAR
SOLVENTS
NON-SOLUBLE
SOLUBILITY
INCREASES AS
POLARITY
DECREASES
SOLUBLE
IB INTERNAL ASSESSMENT
ASSESSED FOR :
DESIGN
DATA COLLECTION AND PROCESS
&
CONCLUSION AND EVALUATION
INVESTIGATE A PARAMETER THAT
AFFECTS THE SOLUBILITY OF SALTS
MADE FROM GROUP 1METALS AND
HALOGENS (GROUP 7)
• Common salt is soluble in water. That does not
mean that we can dissolve infinite amounts of
salt in a specific amount of water. There is a
certain point where no more salt will dissolve.
o How can we measure what is the maximum mass
of salt that can dissolve in a specific volume of
water
o Do we have to measure how much has been
dissolved or is it enough to measure how much
has not been dissolved.
o Do we have to measure the salt itself or we can
measure one of it’s ions.
What factors may effect solubility?
• If we change the metal part of the salt,
will solubility change
• If we change the temperature of water,
will solubility change
• If we change solvent, will the solubility
change
• What other parameters may affect
solubility
SELECT DEPENDENT, INDEPENDENT AND
CONTROLLED VARIABLES, WRITE YOUR SPECIFIC
RESEARCH QUESTION AND DESCRIBE THE
DETAILED PROCEDURE REQUIRED TO
INVESTIGATE THE QUESTION
WRITE THE REPORT INCLUDING ALL
COMPONENTS
CHEMICALS AVAILABLE:
Lithium chloride
Potassium fluoride
Potassium chloride
Potassium bromide
Potassium iodide
Sodium fluoride
Sodium chloride
Sodium bromide